FINAL REPORT 

Corrosion Finishing/Coating Systems For 

DoD Metallic Substrates Based on Non-Chromate Inhibitors 

and UV Curable, Zero VOC Materials

SERDP Project WP-1519 

AUGUST 2010

Prof. Matt O’Keefe 

Missouri S&T

This document has been approved for public release.
Table of Contents 

 Page 

 

List of Acronyms iii 

List of Figures and Tables iv 

Acknowledgments x 

1. Abstract 1 

2. Objective 2 

3. Background 2 

3.1 Non-Chromate Cerium Based Conversion Coatings 3 

 3.2 Zero VOC Coatings 4 

 3.3 UV Curable Coatings 4 

4. Materials and Methods 6 

 4.1 Pre-Treatment Conversion Coatings 6 

 4.2 Substrate Materials 6 

 4.3 MUV Curable Coatings 6 

 4.4 Integrated Coating Systems 7 

 4.5 Characterization 9 

5. Results and Discussion 10 

 5.1 Health and Safety Assessment 10 

 5.2 Cerium-based Conversion Coatings 10 

 5.3 Multifunctional UV (MUV) Curable Coatings 36 

6. Conclusions and Implications for Future Research/Implementation 64

7. Literature Cited 66

8. Appendices 67

8.1 List of Scientific/Technical Publications 67

A. Articles in Peer-Reviewed Journals 67

B. Technical Reports 67

C. Conference or Symposium Scientifically Recognized 68

D. Conference or Symposium Abstracts 68

ii
List of Acronyms 

AES – Auger Electron Spectroscopy 

ASTM – American Society for Testing and Materials 

CeCC – Cerium Conversion Coatings 

CrCC – Chromate Conversion Coatings 

DoD – Department of Defense 

EDS – Energy Dispersive Spectroscopy 

EIS – Electrochemical Impedance Spectroscopy 

EPA – Environmental Protection Agency 

FIB – Focused Ion Beam 

HALS – Hindered Amine Light Stabilizers 

HAPs – Hazardous Air Pollutants 

HMIS – Hazardous Materials Identification System 

IBOA – Isobornyl Acrylate 

LCC – Light Curable Coatings 

MUV – Multifunctional UV 

NCLT – Non-Chromated, Low Temperature 

OSHA – Occupational Safety and Health Administration 

PEA – Phenoxyethyl Acrylate 

PEL – Permissible Exposure Limit 

SEM – Scanning Electron Microscopy 

SERDP – Strategic Environmental Research and Development Program 

TCP – Trivalent Chromium Passivation 

TEM – Transmission Electron Microscopy 

TRI – Toxic Release Inventory 

UV – Ultraviolet 

UVAs – Ultraviolet Absorbers 

VOCs – Volatile Organic Compounds 

XPS – X-ray photoelectron spectroscopy 

XRD – X-ray Diffraction 

iii
List of Figures and Tables 

Figures Page

Figure 1. Left: Existing three layer, hexavalent chromium based corrosion 2 

coating system. Right: Two layer non-chromate, multifunctional UV (MUV) 

curable corrosion coating system under development. 

Figure 2. Auger Electron Spectroscopy depth profiles of spray coated samples 12 

cleaned at (a) 45oC, (b) 55oC, and (c) 65oC showing that the cerium oxide 

thickness increased with cleaning temperature. 

Figure 3. Optical images of alkaline cleaned Al 2024-T3 substrates after 6, 13 

12, and 25 spray cycles. 

Figure 4. Optical images of an acid cleaned Al 2024-T3 substrates after 1 13 

spray cycle. 

Figure 5. Auger depth profiles of Al 2024-T3 panels after (a) alkaline and 14 

(b) acid cleaning. 

Figure 6. Nyquist plots for aluminum 7075-T6 panels prepared using 15 

different methods. 

Figure 7. Nyquist plots for aluminum 7075-T6 panels with CeCCs 16 

deposited on panels prepared using each method. 

Figure 8. Optical images of prepared, uncoated aluminum 7075-T6 panels 17 

after exposure to salt fog for 18 hours A) chemical immersion, B) chemical 

wipe, C) ultrasonic processing, and D) abrasive blasting. 

Figure 9. Optical images of coated aluminum 7075-T6 panels after exposure 18 

to salt fog for 18 hours A) chemical immersion, B) chemical wipe, C) ultrasonic 

processing, and D) abrasive blasting. 

Figure 10. SEM micrographs of CeCC deposited using pH 2.5 and pH 1.0 19 

spray solutions. 

Figure 11. Plot of wt.% Ce detected by EDS vs. wt.% of Ce in the spray solution. 20 

Figure 12. Plot of wt.% Ce detected by EDS vs. ml of H2O2 in the spray solution. 20 

Figure 13. Nyquist plots of CeCC Al 2024-T3 panels in prohesion solution 21 

after 3 hours of testing for panels deposited using 1, 2, 3, and 4 wt.% Ce in 

the deposition solution. 

iv
Figure 14. Nyquist plots of CeCC Al 2024-T3 panels in prohesion solution 22 

after 3 hours of testing for panels deposited using 0, 5, 10, and 20 ml of 

H2O2 in the deposition solution. 

Figure 15. Images of CeCC Al 2024-T3 samples deposited using 0, 5, 10, 22 

and 20 ml of H2O2 in the spray solution following 5 hours of EIS testing 

in prohesion solution. 

Figure 16. a) Scanning electron micrograph of a CeCC deposited on an 24 

Al 2024-T3 panel with no gelatin in the spray solution; b) optical image 

of panel after 2 days of salt spray testing. 

Figure 17. Auger depth profile of a 5 spray cycle CeCC deposited on an 24 

Al 2024-T3 panel with no gelatin in the spray solution. 

Figure 18. a) Scanning electron micrograph of a CeCC deposited on an 25 

Al 2024-T3 panel with 3200 ppm gelatin in the spray solution; b) optical 

image of panel after 7 days of salt spray testing. 

Figure 19. Auger depth profile of a 5 spray cycle CeCC deposited on an 25 

Al 2024-T3 panel with 3200 ppm gelatin in the spray solution. 

Figure 20. Electrochemical impedance of CeCC deposited on an Al 2024-T3 26 

panel with 3200 ppm and no gelatin (0 ppm) in the spray solution. 

Figure 21. a) Scanning electron micrograph of an as deposited (unsealed) 27 

CeCC on an Al 2024-T3 panel; b) optical image of panel after 14 days of 

salt spray testing. 

Figure 22. a) Scanning electron micrograph of a CeCC post treated in a 27 

NH4H2PO4 solution at 85oC for 5 minutes on an Al 2024-T3 panel; b) optical 

image of panel after 14 days of salt spray testing. 

Figure 23. Electrochemical impedance of CeCCs on Al 2024-T3 panels post 28 

treated in different phosphate solutions. 

Figure 24. X-ray diffraction patterns of CeCCs post treated in different 28 

phosphate solutions, and one not post treated (unsealed), on Al 2024-T3 panels. 

Figure 25. Coating thickness as a function of the number of brush or spray 30 

deposition cycles. 

Figure 26. XRD spectra for coatings deposited using three, five, and seven 30 

brush cycles, and three and five spray cycles. 

v
Figure 27. Schematic drawing of reactions that increase the pH near the 31 

surface of Al substrates that causes cerium precipitation from solution. 

Figure 28. Schematic drawing of reactions that occur during CeCC 32 

precipitation from solution. 

Figure 29. Electron micrograph image of a CeCC on an Al 2024-T3 panel 33 

after FIB sectioning. 

Figure 30. Cross sectional micrograph image of an Al 2024-T3 panel after 33 

cleaning (no sub- surface crevices). 

Figure 31. Cross sectional micrograph image of an Al 2024-T3 panel after 34 

CeCC deposition (contains sub-surface crevices). 

Figure 32. Cross sectional micrograph image of an Al 2024-T3 panel after 35 

spraying a H2O2 + NaCl solution on the surface. 

Figure 33. Cross-sectional TEM images of cerium based conversion coatings: 36 

a) as-deposited, b) after 14 days of salt spray testing. 

Figure 34. Auger electron spectroscopy depth profiles of cerium based 36 

conversion coatings: a) as-deposited and b) after 14 days of salt spray testing 

Figure 35. Optical images of Stage 1 Al 2024-T3 coated panels after 3000 38 

hours of neutral salt spray testing. 

Figure 36. Optical images of Stage 1 Al 2024-T3 coated panels after 3000 39 

hours of neutral salt spray testing and removal of the corrosion coatings. 

Figure 37. Auger maps for Cr, Al, and Zn near the scribe for two different 41 

Hybricor 204 MUV coated panels; one not exposed to salt spray and the other 

after passing 3000 hours salt spray. 

Figure 38. Auger maps for Ce, Al, and Zn near the scribe for two different 42 

Hybricor 204 MUV coated panels; one not exposed to salt spray and the other 

after passing 3000 hours salt spray. 

Figure 39. Optical images of Round 2 Al 2024-T3 coated panels after 2000 43 

hours of neutral salt spray testing. 

Figure 40. Optical image of a Round 2 Hybricor 204 MUV coated Al 2024-T3 44 

panel with a TCP conversion coating after 2000 hours salt spray 

Figure 41. Optical image of a Round 2 Hybricor 204 MUV coated Al 2024-T3 44 

panel that did not have a conversion coating (bare) after 2000 hours salt spray. 

vi
Figure 42. Images of integrated coatings on CrCC Al clad Al 2024-T3 after 45 

1000 hours of filiform corrosion testing 

Figure 43. Optical images of MUV coated Al 2024-T3 panels with different 46 

charge levels of Hybricor 204 corrosion inhibitor after 3000 hours of salt 

spray testing. 

Figure 44. Optical images of MUV coated Al 2024-T3 panels on CeCC and 48 

CrCC pretreatments. 

Figure 45. Optical images of wet scribe test results. 49 

Figure 46. Optical images of Al 2024-T3 control panels after 3000 hours of 50 

salt spray corrosion testing. 

Figure 47. Optical images of MUV coated Al 2024-T3 panels with CrCC and 51 

CeCC pretreatments after 3000 hours of salt spray corrosion testing. 

Figure 48. Optical images of MUV coated Al 2024-T3 panels with TCP 52 

pretreatments after 3000 hours of salt spray corrosion testing. 

Figure 49. Optical images of Al 7075-T6 control panels after 3000 hours of 53 

salt spray corrosion testing. 

Figure 50. Optical images of MUV coated Al 7075-T6 panels with CrCC and 54 

CeCC pretreatments after 3000 hours of salt spray corrosion testing. 

Figure 51. Al 2024-T3 chromate control panels after 3000 hours ASTM 59

B117 testing. 

Figure 52. Al 2024-T3 panels with MUV on CrCC after 3000 hours ASTM 59

B117 testing. 

Figure 53. Optical images of Al 2024-T3 panels after 2000 hours of ASTM 60

B117 salt spray testing: a) chromate standard and b) MUV on CrCC. 

Figure 54. Optical images of Al 2024-T3 panels after 2000 hours of ASTM 61

B117 salt spray testing: a) non-chromate standard, b) MUV on TCP, and 

c) MUV on CeCC. 

Figure 55. Optical images of Al 2024-T0 panels after low temperature 62

flexibility tests. 

Figure 56. Optical images of Al 2024-T0 panels after room temperature 62

flexibility tests: a) chromate controls and b) MUV on CrCC. 

vii
viii

Tables Page

Table I Health and Safety Assessment of Coating Materials 10

Table II Summary of CeCC Phosphate Sealing Study 29 

Table III Summary of MUV Testing 37 

Table IV Coating Systems Evaluated (Round 3) 47 

Table V Test Matrix for MUV/CeCC Panels Done at LCC Oct 2008 55 

Table VI Pencil Hardness, Adhesion, Gloss, MEK Rub and Skydrol Results 56 

for MUV/CeCC Panels Done at LCC Oct 2008 

Table VII Salt Spray Ratings for MUV/CeCC Panels Done at LCC Oct 2008 58

Table VIII Summary of MUV Evaluation Results 63
Acknowledgments 

Thanks are due to the many people that contributed to this effort. The project was co-managed 

by Bill Fahrenholtz (Missouri S&T), Ben Curatolo (Light Curable Coatings), and John DeAntoni 

(Boeing). Jim Stoffer’s contributions and dedication to the project while in retirement is both 

admirable and appreciated. The worked done by graduate students Will Pinc, Simon Joshi, 

Daimon Heller, William Gammill, Phillip Jones, and Andrew Thomas along with post-doctoral 

fellows Dr. Ajay Padwal, Dr. Shujiang Geng, Dr. Becky Treu, Dr. Surender Maddela, and Dr. 

Beth Kulp at Missouri S&T has been of the highest quality. The support of the staff of the 

Graduate Center for Materials Research Center at Missouri S&T is gratefully acknowledged. 

Thanks are extended to Donna Ballard at AFRL/ML in the first few years of the project and Gary 

Wright of AFRL/ML in the final year for their support and encouragement. The contributions of 

Dr. Paul Yu and Prof. Tom O’Keefe from the start of the project until the spring of 2008 are 

acknowledged in memoriam. 

The financial support of the Strategic Environmental Research and Development Program and 

guidance of program managers Chuck Pellerin and Bruce Sartwell are gratefully acknowledged. 

x 
1. Abstract

Corrosion resistant coatings containing non-chromate inhibitors and no volatile organic 

compounds were developed and evaluated for DoD applications. The technical effort involved 

cerium based conversion coatings (CeCCs) and ultraviolet (UV) light curable coatings 

containing corrosion inhibitors. This approach would replace the current three layer, 

environmentally unfriendly coating system with a benign, two layer multifunctional UV (MUV) 

coating system. Replacement of corrosion coatings on high strength aluminum alloys used for 

military aerospace applications was the main focus for the technology developed. Work on the 

impact of processing parameters on CeCC corrosion performance, including the use of gelatin in 

the deposition solution and post deposition treatment in phosphate solution, resulted in 

significant improvement in CeCC protection of high strength aluminum from corrosion. The 

identification of sub-surface crevices in the Al substrates that form during CeCC deposition 

helped explain results previously not understood. Application of MUV coatings with Hybricor 

204 corrosion inhibitor repeatedly demonstrated the ability to protect scribed, chromate 

conversion coated Al substrates during ASTM B117 salt spray testing. Drawbar applied MUV 

coatings on CeCC passed salt spray testing while spray applied MUV on CeCC formed blisters 

during ASTM B117 testing. MUV coating properties such as flexibility and fluid resistance were 

improved throughout the project and demonstrated the potential to meet aerospace requirements. 

Results indicate that the technology holds promise for replacing existing environmentally 

hazardous corrosion coatings for military applications. 

 

1 
2. Objective 

The primary objective of this project was to research, develop, characterize, evaluate, integrate, 

and demonstrate an environmentally friendly, chromate-free, zero TRI/VOC/HAPs coating 

system using rare-earth oxide based pretreatments and corrosion inhibiting, multifunctional UV 

(MUV) curable self-priming coatings for metallic substrates that meet or exceed current military 

requirements. The integrated two layer non-chromate coating system replaces the existing three 

layer system (Figure 1), and utilization of a UV curing system will greatly reduce the time 

required to paint DoD equipment. Aluminum alloy substrates commonly used in military 

aerospace applications were the main focus of the work. The integration, compatibility, and 

effectiveness of the novel low and high gloss ultraviolet light curable, corrosion preventing, 

MUVs with rare-earth based conversion coatings has the potential to meet or exceed all of the 

objectives contained in the SERDP statement of need PPSON-06-04. 

Chromate Conversion Coating

Organic Top Coat 

Strontium Chromate Primer 

Metallic Substrate 

MUV Coating 

Non-Chromate Conversion Coating 

Metallic Substrate 

Figure 1. Left: Existing three layer, hexavalent chromium based corrosion coating system. Right: 

Two layer non-chromate, multifunctional UV (MUV) curable corrosion coating system under 

development. 

3. Background 

Military corrosion protection coating systems typically consist of a metal pretreatment 

conversion coating followed by an epoxy primer and a polyurethane topcoat. Although very 

effective at preventing corrosion of the underlying metallic substrate, these coatings contain 

volatile organic compounds (VOCs), hazardous air pollutants (HAPs) and chemicals listed on the 

toxic release inventory (TRI). The chromate corrosion inhibitors used in the conversion coating 

in direct contact with the metallic substrate, as well as in the epoxy primer, present a serious 

health risk to workers that paint and de-paint military assets. In addition, the epoxy primer is 

formulated at 340 grams per liter VOC while polyurethane topcoats are typically formulated at 

420 grams per liter VOC and are crosslinked with hazardous isocyanates that are on the TRI. 

The annual cost of corrosion to the U.S was estimated at $276 billion dollars. According to the 

“Cost of Corrosion” study published by CC Technologies and NACE International, corrosion 

and metal wastage arising from oxidation as caused by exposure to the elements and reactivity 

between dissimilar materials costs the U.S. military about $20 billion annually [1]. Aluminum 

alloys important in both military and civilian aircraft are prone to such corrosion. The result is 

an annual maintenance cost for Navy aircraft of about $800 million per year. According to USAF 

2 
sources, aircraft painting/stripping/repainting processes and handling associated hazardous waste 

is one of the highest cost maintenance activities. Chromates are an essential part of the present 

coating systems used on many DoD substrates. 

The EPA regulates chromium and its compounds under the Clean Air Act, Clean Water Act, 

Comprehensive Environmental Response, Compensation and Liability Act, Resource 

Conservation and Recovery Act, Superfund Amendments and Reauthorization Act, and Toxic 

Substances Control Act. Federal, state, and local agencies have issued regulations that limit or 

prohibit the use of chromate- containing materials. OSHA regulates the amount of hexavalent 

chromium to which workers can be exposed and has reduced the Permissible Exposure Limit 

(PEL) for hexavalent chromium and for all Cr(VI) compounds in construction, shipyards, and 

general industry from the previous 52 μg/m3

 to 5 μg/m3 as an 8 hour time-weighted average [2]. 

This also includes provisions for employee protection such as preferred methods for controlling 

exposure, respiratory protection, protective work clothing and equipment, hygiene areas and 

practices, medical surveillance, hazard communication, and record keeping. These regulations 

will severely impact the use of hexavalent chromium throughout the DoD and the defense 

industry. Use of hexavalent chromium compounds is also tightly controlled by EPA regulations 

issued under the Toxic Substances Control Act, Safe Drinking Water Act, Clean Water Act, 

Clean Air Act, Resource Conservation Recovery Act, Comprehensive Environmental Response, 

Compensation and Liability Act; and by OSHA under the Occupational Safety and Health Act. 

Chromium has been found in 1,036 of 1,591 National Priority List (Superfund) sites identified by 

the EPA. Development of a chrome free alternative corrosion protection coating system would 

not be subject to these restrictions while maintaining the corrosion protection needed for DoD 

platforms. 

There has been extensive research on the development of alternative treatments of metallic 

surfaces for corrosion protection. Among the major classes of chromate alternatives are cerium, 

cobalt, molybdenum, and manganese-based coatings, titanium and zirconium fluorocomplexes, 

hydrotalcites, boehmites and silanes, and inherently conducting polymers. Recent work includes 

some of the current efforts investigating the use of magnesium rich primers and conducting 

polymers to protect aluminum alloys, controlled release of inhibitors from polyaniline 

conductive polymers, and the use of cerium modified bentonite clay for corrosion inhibition and 

sensing. 

3.1 Non-Chromate, Cerium Based Conversion Coatings 

The non-chromate coatings group at Missouri S&T has identified cerium compounds as 

potentially viable corrosion inhibitors and replacements for chromate conversion coatings on 

aluminum alloys. Success in developing the technology has led to several patent applications 

being filed and issued [3,4]. Work at Missouri S&T on conversion coatings over the past few 

years has involved the deposition of cerium oxide-based conversion coatings from aqueous 

solutions. Feasibility studies on other rare-earth compounds as well as electrochemically active 

elements have been conducted. 

3 
Initial attempts to deposit cerium-based conversion coatings on aluminum alloys consisted of 

immersion in a cerium chloride solution for a period of several days, which resulted in the 

deposition of a thin, cerium (III) oxide layer [5]. Some of the methods used to reduce coating 

deposition time have included galvanostatically polarizing the aluminum surface in an aqueous 

CeCl3 bath or boiling the panel in an aqueous cerium salt solution in combination with an anodic 

treatment in Na2MnO4. The addition of hydrogen peroxide to a cerium chloride bath can reduce 

the coating time to approximately ten minutes [6]. This method can be further enhanced by the 

use of a deoxidizer to activate the surface before immersion into the coating bath [7]. 

Cerium-based conversion coatings have been deposited using electrolytic (current-driven) and 

spontaneous (immersion) deposition methods. Processes that deposit cerium-based conversion 

coatings that meet the DoD standard by providing corrosion protection for 336 hours (2 weeks) 

in ASTM B117 salt spray testing have been developed for both aluminum alloy 7075-T6 and 

2024-T3. Mechanistic studies revealed that coating deposition occurred due to an 

electrochemically-driven increase in the pH near the alloy panel surface that led to the 

precipitation of insoluble hydrated Ce4+ compounds that attached to the panel surface [8]. Work 

done on this project focused on developing and optimizing a spray process for deposition of 

cerium-based conversion coatings on aluminum alloy 2024-T3. Based on work done at Missouri 

S&T, surface preparation, deposition solution composition, and post treatment steps significantly 

impact the corrosion resistance of cerium oxide conversion coatings. 

3.2 Zero VOC Coatings 

Zero VOC corrosion coatings can be formulated by substituting VOC exempt solvents that are 

not photo-chemically reactive. Non-HAP VOC exempt solvents, such as acetone, can be used in 

coatings formulations. In some cases use of these solvents increases the flammability of the 

coating and can have a negative impact on appearance and application parameters. More 

desirable, zero VOC corrosion coatings formulated with water have been introduced to the 

marketplace, but it is not known if these coatings will meet all of the stringent performance 

requirements of military specifications, necessitating a different approach. 

3.3 UV Curable Coatings 

Ultraviolet (UV) light curable coatings are a class of coatings that can be formulated to be 

solvent free, and therefore zero VOC. UV curing is a photochemical process by which a liquid 

coating changes to a cross-linked solid polymer through exposure to UV radiation without the 

need for isocyanate cross-linking agents. Benefits of UV technology include zero VOC, HAPSfree coatings that fully cure in seconds, resulting in faster throughput and labor savings, 

consistent with the needs outlined in the statement of needs for this project. UV technology is 

recognized as a Best Available Control Technology and a Lowest Achievable Emission Rate 

technology by the EPA. An ultraviolet light curable coating qualifies as a “Superclean” 

technology defined by the Southern California South Coast Air Quality Management District. 

This allows for immediate installation of UV processes without the need for a permit. 

Ultraviolet curing is one of the radiation curing techniques that are used in coatings, inks, 

adhesives and sealants. UV curable coatings can be formulated to be 100% solids, and can be 

instantaneously polymerized and cross-linked to give films that are decorative and functional [9]. 

4 
The original driving forces behind the commercialization of UV-curing technology were energy 

saving and freedom from solvents [10]. Improved economics, and efficiency result from 

instantaneous curing characteristic in the case of UV polymerization. Since all of the 

formulation reacts or remains effectively within the final film, UV curable coatings are near zero 

VOC. As the pressure to reduce VOC continues to mount, UV cured coatings are becoming 

more attractive. There are two classes of UV-curable coatings, free radical (mostly acrylate) and 

cationic (epoxy) depending upon the nature of photoinitiators and resin chemistry. 

Improvement in the coating/substrate interaction is one of the most critical areas of performance 

in the practical application of UV curing. Due to adsorption, the substrate/coating interface 

receives the lowest dose of UV radiation and the interaction between the coating and the 

substrate can inhibit the cure [11]. Pigment selection also plays an important role in the overall 

curing characteristics of pigmented systems. In general, the larger the pigment particle size, the 

smaller the surface area and, therefore, the better the curing. UV cured coatings that are used for 

exterior application usually require the use of light stabilizers to prevent degradation of the resin 

system due to damaging UV radiation. The two light stabilizers typically used are ultraviolet 

absorbers (UVAs) and hindered amine light stabilizers (HALS). HALS have, in most cases, 

little or no impact on the cure properties of the photopolymers. UVAs, however, can compete 

with photoinitiators for the available light and therefore have an impact on the cure speed of 

most formulations [12]. Incorporation of inorganic corrosion inhibiting compounds into a UV 

curable matrix results in a multifunctional UV (MUV) coating that provides the weathering 

protection of a top coat and the corrosion protection of a primer into a single layer. 

5 
4. Materials and Methods 

The overlap of the technical approach necessitated that all members contributed to each task and 

significant interaction occurred within each task. Responsibility for the project tasks was 

distributed by expertise and capabilities in each area, cognizant that each team member 

contributed to every task. Missouri S&T was the lead organization for non-chromate conversion 

coatings, LCC headed up the formulation and application of MUV curable coatings, and Boeing 

was responsible for integration, evaluation and implementation. 

4.1 Substrate Materials 

Aluminum alloys 2024-T3 and 7075-T6 were used throughout the study. Panels were sheared 

from large sheets into either 1” x 3” or 3” by 6” size for studies. The bulk chemical composition 

of Al 2024-T3 is 90.7-94.7 wt% Al, 3.8-4.9 wt% Cu, 1.2-1.8wt% Mg, 0.3-0.9 wt% Mn, 

maximum of 0.5 wt% Fe, maximum of 0.1wt% Cr, maximum of 0.5wt% Si, maximum of 0.15 

wt% Ti, maximum of 0.25 wt% Zn, balance other trace elements. The bulk chemical 

composition of Al 7075-T6 is 87.1-91.4 wt% Al, 5.1-6.1wt% Zn, 1.2-2.0wt% Cu, 21.-2.9wt% 

Mg, maximum of 0.3wt% Mn, maximum of 0.5 wt% Fe, 0.18-28wt% Cr, maximum of 0.4wt% 

Si, maximum of 0.20wt% Ti, balance other trace elements. 

4.2 Pre-Treatment Conversion Coatings 

Spray deposition of cerium oxide based conversion coatings onto Al 2024-T3 and Al 7075-T6 

panel substrates was the focus of the pre-treatment technical efforts. Cleaning of the substrates 

prior to coating was done by an isopropyl alcohol rinse; an acid, alkaline, or a combination of 

acid and alkaline solutions; and water rinses. The substrates were kept wet throughout the 

process. Unless otherwise noted, the deposition solution was 250 ml in volume with a nominal 

composition of 4 wt.% CeCl3·xH2O, 20 ml of 30 vol.% H2O2, 0.8 g of organic gelatin with the 

balance water. Spray deposition was accomplished using a commercially available detail air 

gun. The panels were placed upright at an angle of ~60° to the horizontal and sprayed evenly for 

a few seconds, followed by a 35 second delay; this was considered one spray cycle. Repetition 

of spray cycles was used to build up coating thickness and improve coating uniformity. The 

hydrated cerium oxide that was deposited by this method was then post treated, or “sealed”, in an 

85°C phosphoric acid based solution at pH 4.5 to convert the coating, either partially or 

completely, into hydrated cerium phosphate. All panels were sealed in a phosphate solution 

unless otherwise noted. Chromate conversion coated panels used for controls during evaluation 

were produced at Boeing or obtained from commercial vendors. 

4.3 MUV Curable Coatings 

Several formulations of MUV curable coatings were developed and evaluated throughout the 

project. Corrosion inhibitors evaluated included Hybricor 204, HT-13, and HT-20 from Wayne 

Pigments and praseodymium oxide based materials from Deft. The initial studies used 36% 

inhibitor loading; subsequent ladder studies investigated loadings of 0%, 7%, 15%, 22%, 29% 

and 36%. Isobornyl acrylate (IBOA) and phenoxyethyl acrylate (PEA) were the two monomers 

evaluated. Dispersants, fillers, photoinitiators, stabilizers, and other additives were also 

6 
evaluated. Five sets (rounds) of MUV coatings were evaluated. The first two rounds were 

deposited by drawbar with a 36% inhibitor loading. The final three rounds used Hybricor 204 

inhibitor at a loading of 29% and were deposited using a spray gun. The MUV formulation was 

heated to ~105°F prior to spray application in order to produce consistent flow characteristics. 

Panels were mounted horizontally and the MUV was sprayed using an overlapping pattern until a 

final film thickness of ~0.002” (2 mils) was achieved. Curing was done sequentially using 10” 

long, 600W/in V and H ultraviolet lamps from Fusion, Inc. The panels were passed under the 

bulbs at a conveyor speed of 1”/sec and at a distance of 2.5” from the lamps. This setup resulted 

in an initial exposure of the panels to a V bulb for about 0.5 second and then to an H bulb for an 

additional 0.5 second, which fully cured the coatings. 

4.4 Integrated Coating Systems 

Evaluation of the integrated corrosion coating systems under development against standard test 

procedures was done throughout the year. Cerium conversion coated panels were made at 

Missouri S&T and sent to LCC for MUV application in most cases, with one set of panels made 

at LCC by S&T students in October of 2008. Commercial chromate and non-chromate 

comparison systems were used as control samples during testing. Evaluation of the coatings 

were done at Boeing-St. Louis and included neutral salt spray testing, wet adhesion tests, 

Skydrol fluid resistance, low and room temperature flexibility, filiform corrosion testing, and Xe 

arc weathering. Boeing’s testing procedures are listed below. The ratings criteria for evaluating 

scribed panels was developed at Boeing to provide a relative performance evaluation; panels 

with 1,A ratings are considered the best. 

Boeing Test Procedures

Surface Treatment: 

Coordinate test panel chromate surface treatments with the chemical process area. Cerium 

conversion coating will be performed by Missouri S&T. 

Primer and Topcoat Application: 

Apply primer and topcoat per the manufacturer’s instructions. Apply primer to dry film 

thickness between 0.7 and 1.3 mils. Apply topcoat to a dry film thickness between 1.7 and 2.3 

mils. Let topcoat air dry two weeks prior to test. Measure and record all coating thicknesses. 

UV coating will be applied by Light Curable Coatings. 

3000 hour 5% salt spray: 

Panels shall be scribed with an “X” across the test face using a NewHermes engraving machine. 

The scribe lines should penetrate to the substrate. Wrap the edges and back of the test panels 

with tape. Expose the test panels to 5% neutral salt fog for 3000 hours per ASTM B 117. 

Check the panels for corrosion at 1000, 2000 and 3000 hours. 

For each evaluation period, provide the following: 

Rank primers from best to worst. 

Rank the panels alpha/numerically using the ranking method established by the laboratory. 

7 
Ratings Criteria for Panels after ASTM B117 Testing 

Code Description 

1 Scribe line beginning to darken or shiny scribe. 

2 Scribe lines > 50% darkened. 

3 Scribe line dark. 

4 Several localized sites of white salt in scribe lines. 

5 Many localized sites of white salt in scribe lines. 

6 White salt filling scribe lines. 

7 Dark corrosion sites in scribe lines. 

8 Few blisters under primer along scribe line. (<12) 

9 Many blisters under primer along scribe line. 

10 Slight lift along scribe lines. 

11 Coating curling up along scribe. 

12 Pin point sites/pits of corrosion on organic coating surface (1/16” to 1/8” dia.).

13 One or more blisters on surface away from scribe. 

14 Many blisters under primer away from scribe. 

15 Starting to blister over surface. 

Code Scribe line ratings - corrosion creepage beyond scribe 

A. No creepage 

B. 0 to 1/64 

C. 1/64 to 1/32 

D. 1/32 to 1/16 

E. 1/16 to 1/8 

F. 1/8 to 3/16 

G. 3/16 to 1/4 

H. 1/4 to 3/8 

Provide a checklist of all the types of corrosion / defects at each interval: 

After the 3000-hour exposure period get photographs taken of the test panels. Strip one of the 

test panels with Turco 5469 or equivalent paint stripper and get a photograph of the stripped 

panels. 

Scribed Wet Tape Adhesion Tests: 

Perform a scribed wet tape adhesion test on the test panels as follows: Scribe two parallel lines 

with an X-acto knife along the 6" panel direction, approximately 3/4" apart and 2 inches long. 

Scribe an "X" between the two parallel lines. Apply 3M #250 tape parallel to the first two 

parallel scribe lines. Roll a 4 lb., 60 durometer rubber roller across the tape 4 times back and 

forth. Immediately remove the tape at a 45-degree angle with one abrupt motion while holding 

the panel steady with the opposite hand. Examine the test panel for removal and uplifting of the 

coating. Evaluate the adhesion of the panels per Method A of ASTM D 3359 - 97 and provide 

the rating of 5A, 4A, 3A, 2A, 1A, or 0A. Also provide the percentage of the coating removed. 

8 
Low Temperature Flexibility: 

Expose panels in a cold box maintained at -60°F+/-5°F for 5 hours. After exposure the panels 

shall be bent over a 1⁄2 inch mandrel which has been conditioned at the same temperature. 

Examine for cracks with unaided eye. 

GE Room Temperature Reverse Impact Flexibility: 

Using the GE impact tester the flexibility shall be 20% minimum. Test method shall be ASTM 

D2794. Do not allow the impacter to bounce on the panel. Report results under 10x 

magnification and with the unaided eye. 

1000 Hour Filiform Corrosion: 

The test panels shall be scribed with an “X” across the test face using a New Hermes engraving 

machine. The scribe lines should penetrate to the substrate. Wrap the edges and back of the test 

panels with tape. Place the panels vertically in a dessicator containing 12N hydrochloric acid for 

one hour. Within 5 minutes of removal from the desiccator, place the panels in a humidity 

cabinet maintained at 104 +/- 4 o F and 80 +/- 5% RH for 1000 hours. After removal from the 

humidity cabinet, examine the test panels for filiform corrosion, as described in ASTM D2803. 

The applied coating shall exhibit no filiform corrosion extending beyond 1⁄4 in. from the scribe. 

A majority of the filaments shall be less than 1/8 in. in length. Rank coatings from best to worst. 

After the 1000-hour exposure period, photograph the test panels. Strip one of the test panels 

with Turco 5469 or equivalent paint stripper and photograph the stripped panels. 

Xenon Arc Weather Resistance: 

The test panels shall be exposed for 1000 hours in a xenon-arc weatherometer that is cycling 

between 102 minutes of light only, and 18 minutes of light and water spray. Check panels for 

initial color (E value), 85 and 60-degree gloss and at 500 and 1000 hours for Delta E and gloss. 

30-day Room Temperature Skydrol Resistance 

Determine the initial pencil hardness of the film per ASTM D3363. Scribe the panels and wet 

with Skydrol LD-4 once daily for 30 days at ambient temperature. Remeasure the pencil 

hardness after this period. After immersion there shall be no softening below a hardness of H, 

any blistering, any wrinkling, or loss of adhesion. 

4.5 Characterization 

Electrochemical and materials characterization techniques were used throughout the project. 

Surface analysis was done using Auger electron spectroscopy (AES) and x-ray photoelectron 

spectroscopy (XPS), imaging and chemical analysis was done using scanning electron 

microscopes (SEMs) with energy dispersive spectroscopy (EDS) capability, and cross sections 

were made in a focused ion beam (FIB) microscope. Electrochemical evaluations included 

potentiodynamic polarization scans and electrochemical impedance spectroscopy (EIS). 

Specific details are provided in the publications listed at the end of the report, with articles by S. 

Geng, et al, “Screening Study of Spray Solution Parameters for Depositing Cerium Based 

Conversion Coatings on Al Alloy 2024-T3”, J. Applied Electrochemistry, 40, 551, (2010) and 

W. Pinc, et al, “Effects of acid and alkaline based surface preparations on spray deposited cerium 

9 
based conversion coatings on Al 2024-T3”, Applied Surface Science, 255, 4061 (2009) 

representative of the types of characterization that were done. 

5. Results and Discussion 

5.1 Health and Safety Assessment 

Boeing conducted an environmental, health, and safety assessment of the coating materials and 

systems being used on the project per the Hazardous Materials Identification System (HMIS), 

including the chromate materials used as controls. Shown in Table I below are the results of the 

assessment. The top two rows are for the two-layer CeCC and MUV coating system and the 

three lower rows are for the current chromate coating system. The assessment indicated that the 

materials used in the project are much more benign than the standard chromate system. 

Table I - Health and Safety Assessment of Coating Materials

 Health 

(HMIS 

Rating) 

Reactivity

(HMIS 

Rating) 

Flammability 

(HMIS 

Rating) 

Carcinogenic 

(Cal. Prop. 65)

Teratogenic 

(Cal. Prop. 65) 

SARA 

313 

VOC 

Cerium 

Oxide 

1 1 0 No No No None 

MUV 2 2 1 No No Yes None 

 

Chromate 

conv. 

coating 

3 1 0 Yes No Yes None 

Epoxy 

chromate 

primer 

3 1 3 Yes No Yes 334 g/l 

Polyurethane 

topcoat 

4 1 3 No Yes Yes 420 g/l 

5.2 Cerium-based Conversion Coatings 

The corrosion performance of CeCCs on high strength aluminum alloys was found to be 

dependent on many factors, especially the preparation of the surface prior to deposition, the 

solution chemistry of the deposition solution, and post-deposition treatment in phosphate 

solutions. Development of non-spray deposition methods were investigated for possible field 

application. Characterization of the coatings was done throughout the project to provide insight 

into coating formation that led to proposal of a deposition mechanism for CeCCs. 

10 
Surface Preparation

Alkaline Cleaning Temperature

Studies during the initial phase of the project investigated the influence of alkaline cleaning 

temperature on coating deposition and corrosion performance. The alkaline cleaner used, Turco 

4215-NLCT from Henkel Corp., has a recommended operating range of 40-60°C. Prior work on 

Al 7075-T6 substrates had identified 55°C as the optimum cleaning temperature for immersion 

(dip) CeCCs. Since the focus of this project was on using a spray deposition process, a series of 

experiments was conducted to determine if a 55°C was the preferred alkaline cleaning 

temperature. 

During spray deposition on Al 7075-T6 it was observed that the deposition rate was lower on 

panels cleaned at 45oC compared to panels that were cleaned at 55oC. After 20 sprays, the panels 

had changed color slightly, but only to a light orange, and the coatings were not as uniform as for 

a standard panel cleaned at 55oC. Therefore, more than 20 spray cycles were needed for panels 

cleaned at 45oC before the color of the panels changed from gray to a dark orange color. The 

panels cleaned at 55oC only required 20 spray cycles and they coated evenly and changed color 

as expected. The panels cleaned at 65oC changed color the fastest, but spraying continued for the 

standard number of 20 spray cycles over 15 minutes to ensure a thick coating. There was little to 

no measurable difference in the microstructures of the coatings examined using optical and 

electron microscopes. However, Auger depth profiling analysis indicated that the thickness of 

the cerium oxide layer increased from 100 nm for panels cleaned at 45oC, to 143 nm for panels 

cleaned at 55oC, and to 296 nm for panels cleaned at 65oC (Figure 2). Therefore, the color of the 

CeCC was a reasonable indication of coating thickness and could be used as process control 

parameter by operators in the field. Chemical surface analysis of the substrates after cleaning, 

but before CeCC deposition, did not reveal any significant differences in composition after using 

the different cleaning temperatures. 

11 
 100 

O 

Al 

Ce 

Figure 2. Auger Electron Spectroscopy depth profiles of spray coated samples on Al 7075-T6 

cleaned at (a) 45oC, (b) 55oC, and (c) 65oC showing that the cerium oxide thickness increased 

with cleaning temperature. 

(c) 

(a) (b) 

Al 

O 

Ce 

296 nm

Al 

Ce 

O 

 143 

Acid Activation

Standard cleaning procedures for 2024-T3 Al alloys initially used just an alkaline solution, Turco 

4215 NCLT, prior to spray deposition. This resulted in a surface that was able to be evenly 

coated with ~300 nm of hydrated cerium oxide (CeO2•xH2O) after approximately 30 spray 

cycles. It is more desirable from a manufacturing standpoint to have fewer spray cycles so work 

was done to determine methods to decrease the number of spray cycles to obtain ~300-400 nm 

thick films with fewer spray cycles. It was determined that a 1 wt% sulfuric acid activation after 

an alkaline clean, but prior to deposition, on Al 2024-T3 reduced the number of spray cycles 

needed for a 400 nm thick film to five, with one spray cycle on acid activated panels resulting in 

a film ~275 nm in thickness. Shown in Figure 3 are a series of images from alkaline (only) 

cleaned Al 2024-T3 panels after a number of spray cycles while Figure 4 depicts an acid 

activated panel after just one spray cycle. It is clear from the images that very little coating 

12 
forms on the alkaline cleaned (only) panel up to ~10 spray cycles while a single spray cycle on 

acid activated substrates resulted in a fairly uniform coating. 

 6 sprays 12 sprays 25 sprays 

Figure 3. Optical images of alkaline cleaned Al 2024-T3 substrates after 6, 12, and 25 spray 

cycles. 

 1 spray 

Figure 4. Optical images of an acid cleaned Al 2024-T3 substrates after 1 spray cycle. 

In order to determine why the two cleaning processes produced such a dramatic difference in 

deposition rate, Auger electron spectroscopy (AES) was used to characterize the substrates after 

cleaning but prior to deposition. Shown in Figure 5 are AES depth profiles of Al 2024-T3 

substrates after alkaline cleaning in Turco alkaline (Figure 5a) and activation in 1 wt% sulfuric 

acid (Figure 5b) solutions. The profiles show that the surface of the alkaline cleaned substrate 

had a significant amount of Mg and ~25 nm thick oxide film, along with little Cu. In contrast, 

the acid activated substrate surface had very little Mg, only a ~5 nm thick oxide, but ~10 at.% Cu 

after acid cleaning, which was an indication that the acid was more effective at removing the 

MgO/Al2O3 layer and exposing the underlying metal surface. The copper on the surface, most 

likely from intermetallic compounds in the alloy, acts as cathodic sites that facilitate precipitation 

of cerium oxide during deposition and increases the deposition rate. Concentrations of Cu and 

Mg in Figure 5 are different from the bulk values due to surface enrichment and depletion that 

occurs during heat treatment. 

13 
 (a) 

 (b) 

Figure 5. Auger depth profiles of Al 2024-T3 panels after (a) alkaline and (b) acid cleaning. 

Alternative Surface Preparation Methods

The alkaline and acid cleaning described above was done by immersion of the panels in a beaker 

of solution. This method would not be feasible for field repair and touch ups on existing aircraft. 

During the final year of the program alternative methods to prepare surfaces for coating were 

studied, including hand application (wiping) of the cleaning solutions, ultrasonic agitation in 

water, and abrasive media (“sand”) blasting. These methods were compared to the standard 

immersion processes. After the alternative surface preparation techniques the aluminum surfaces 

were optically different from the unprepared surfaces and from each other. Immersion prepared 

and chemically wiped panels were both dark in color, but the immersion cleaned panels tended to 

be darker than the chemical wiped ones. Ultrasonically processed panels did not appear different 

than unprepared panels. Abrasively blasted panels had visibly rough surfaces that tended to be a 

brighter color than unprepared panels. 

14 
Electrochemically, treated Al 7075-T6 surfaces were more active than unprepared panels. 

Impedance scans (Figure 6) showed the blasted panels had the lowest charge transfer resistance 

(3.4 kΩ-cm

2

) and that the ultrasonically cleaned panels had the highest charge transfer resistance 

(5 kΩ-cm2

). The tests found that all of the prepared panels had higher corrosion currents and 

lower charge transfer resistances than as-received panels and, therefore, had higher corrosion 

rates. Based on these results, the protective oxide layer was affected by the alternative surface 

preparation techniques. 

-3000

-2500

-2000

-1500

-1000

-500

0

0 1000 2000 3000 4000 5000

Immersion ( )

Chemical wipe ( )

Ultrasonic ( )

Abrasive blast ( )

Z’ (Ω-cm^2)

Z” (

Ω-cm^2)

-3000

-2500

-2000

-1500

-1000

-500

0

0 1000 2000 3000 4000 5000

Immersion ( )

Chemical wipe ( )

Ultrasonic ( )

Abrasive blast ( )

Z’ (Ω-cm^2)

Z” (

Ω-cm^2)

Figure 6. Nyquist plots for aluminum 7075-T6 panels prepared using different methods. 

Electrochemical tests performed on alternatively prepared panels coated with CeCC found an 

increase in the measured corrosion resistance after coating. Results varied with the surface 

preparation used. Electrochemical impedance spectroscopy (EIS) tests found variation in charge 

transfer resistance values for panels with CeCCs, from about 5 kΩ-cm

2

 for the abrasively 

prepared coating to about 44 kΩ-cm

2

 for the immersion prepared coating (Figure 7). The charge 

transfer resistance values for panels with CeCCs were higher than the uncoated surfaces, but the 

immersion prepared and chemically wiped panels improved the most, consistent with the 

potentiodynamic scans. All of the coatings offered some protection compared to the prepared 

panels. 

15 
-20000

-15000

-10000

-5000

0

5000

10000

0 10000 20000 30000 40000

Immersion ( ) 

Chemical wipe ( )

Ultrasonic ( )

Abrasive blast ( )

Z’ (Ω-cm^2)

Z” (

Ω-cm^2)

-20000

-15000

-10000

-5000

0

5000

10000

0 10000 20000 30000 40000

Immersion ( ) 

Chemical wipe ( )

Ultrasonic ( )

Abrasive blast ( )

Z’ (Ω-cm^2)

Z” (

Ω-cm^2)

Figure 7. Nyquist plots for aluminum 7075-T6 panels with CeCCs deposited on panels prepared 

using each method. 

Salt spray testing was also performed to compare corrosion performance of panels with CeCCs. 

Figure 8 contains images of the uncoated, prepared panels after 18 hours of exposure. The salt 

spray tests on the uncoated panels show the same trend as the electrochemical tests on the 

uncoated panels. The abrasively blasted panel corroded the most; it had a continuous layer of 

corrosion product on the surface. The immersion prepared panel had many large pits with tails, 

while the chemically wiped panel had fewer pits and smaller tails. The ultrasonically prepared 

panel had the fewest pits and the least amount of tailing of the prepared panels. Panels with 

CeCCs were less corroded than the uncoated panels (Figure 9). The salt spray results were 

consistent with the electrochemical tests on the coated panels. The most corroded panel was the 

blasted panel, again with a continuous corrosion product layer. The CeCC on the immersion 

prepared and chemically wiped panels performed the best in salt spray, with few pits and little 

tailing. The immersion pretreatment had slightly fewer pits. The ultrasonically prepared panel 

was the least corroded of the uncoated panels but the coating on the ultrasonically prepared panel 

did not protect as well as the coatings on the immersion prepared and the chemically wiped 

panels. 

16 
A B

C D

Figure 8. Optical images of prepared, uncoated aluminum 7075-T6 panels after exposure to salt 

fog for 18 hours A) chemical immersion, B) chemical wipe, C) ultrasonic processing, and D) 

abrasive blasting. 

17 
A B

C D

Figure 9. Optical images of coated aluminum 7075-T6 panels after exposure to salt fog for 18 

hours A) chemical immersion, B) chemical wipe, C) ultrasonic processing, and D) abrasive 

blasting. 

18 
Deposition Conditions

pH, Ce and H2O2 Concentration Effects

Efforts to develop and optimize cerium oxide based conversion coatings on high strength 

aluminum alloy substrates focused on how the pH, cerium, and H2O2 concentration in the spray 

solution influenced coating formation and corrosion performance. The influence of pH (1.0-2.5), 

Ce concentration (1 to 4 wt.%), and H2O2 concentration (0 to 20 ml per 250 ml) on coating 

morphology, thickness, and corrosion performance after 5 spray cycles were investigated. It was 

found that the amount of Ce detected in the film by EDS in the SEM was ~30 wt% for all of the 

pH values evaluated but there were fewer cracks observed in the coating from pH 2.0 or 2.5 as 

compared to pH of 1.0 or 1.5 (Figure 10). As the concentration of Ce in the spray solution was 

increased from 1 to 4 wt.%, however, the amount of Ce detected on the surface by EDS 

increased from ~8 wt.% Ce in the film from the 1 wt.% Ce solution to ~30 wt.% Ce in the film 

for the 4 wt.% Ce solution (Figure 11), an indirect but reproducible method of evaluating coating 

thickness. As the coating thickness increased the corrosion resistance also improved up to 4 

wt.% Ce in solution but then degraded beyond that point. Similarly, as the hydrogen peroxide 

concentration increased from 0 to 20 ml, the amount of Ce detected by EDS increased (Figure 

12) with peroxide concentrations above 20 ml resulting in poorer corrosion performance. 

 pH 2.5 

2.5 

20 μm 

 pH 1.0 

1.0 

20 μm 

Figure 10. SEM micrographs of CeCC deposited using pH 1.0 and pH 2.5 spray solutions. 

19 
 

Figure 11. Plot of wt.% Ce detected by EDS vs. wt.% of Ce in the spray solution. 

0

10

20

30

40

012345

CeCl3·7H2O concentration of 

solution (wt.%)

Ce wt.% in coatings

·

Figure 12. Plot of wt.% Ce detected by EDS vs. ml of H2O2 in the spray solution. 

20 
In a similar fashion, EIS measurements were made on CeCC panels in prohesion solution for up 

to 5 hours and the data indicated that the higher the impedance, or graphically the larger the loop 

and intercept value on a Nyquist plot, the better the performance during salt spray testing. 

Nyquist plots for Al 2024-T3 panels with CeCC after 3 hours in prohesion solution for coatings 

deposited with different concentrations of Ce (Figure 13) and H2O2 (Figure 14) indicated that as 

both the Ce and H2O2 concentration in the solution increased the impedance of the CeCC panel 

(which had been sealed in a phosphate solution) also increased. Note that no coating was 

deposited in the case of 0 ml of H2O2 since no oxidizer was present in the solution. The 

difference in pitting corrosion after five hours of EIS testing was also confirmed visually in that 

the higher the impedance, the better the corrosion resistance. Shown in Figure 15 are images of 

the peroxide test samples after 5 hours of EIS testing in prohesion solution. 

Figure 13. Nyquist plots of CeCC Al 2024-T3 panels in prohesion solution after 3 hours of 

testing for panels deposited using 1, 2, 3, and 4 wt.% Ce in the deposition solution. 

3.0-h

0.0 5.0x104 1.0x105 1.5x105 2.0x105

0.0

5.0x104

1.0x105

1.5x105

 4 wt.%

 3 wt.%

 2 wt.%

 1 wt.%

- ZIm (

Ω cm 2

)

ZRe (Ω cm 2)

0 1x104 2x104 3x104 4x104 0

1x104

2x104

3x104

- ZIm (

Ω cm 2

)

ZRe (Ω cm 2)

21 
Figure 14. Nyquist plots of CeCC Al 2024-T3 panels in prohesion solution after 3 hours of 

testing for panels deposited using 0, 5, 10, and 20 ml of H2O2 in the deposition solution. 

Figure 15. Images of CeCC Al 2024-T3 samples deposited using 0, 5, 10, and 20 ml of H2O2 in 

the spray solution following 5 hours of EIS testing in prohesion solution. 

0 ml 5 ml 

10 ml 20 ml 

3.0-h

0.0 5.0x104 1.0x105 1.5x105 2.0x105

0.0

5.0x104

1.0x105

1.5x105

 20ml

 10ml

 5ml

 0ml

- ZIm (

Ω cm 2

)

ZRe (Ω cm 2)

0 1x104 2x104 3x104 4x104 0

1x104

2x104

3x104

- ZIm (

Ω cm 2

)

ZRe (Ω cm 2)

22 
Gelatin Addition

The addition of a water soluble gelatin to the cerium-based conversion coating solution greatly 

improved the salt spray corrosion performance of the CeCC on high strength aluminum 

substrates that have been post-treated (those without post-treatment do poorly in salt spray 

regardless). Video recording of the deposition process had demonstrated that the presence of 

gelatin in the solution modifies the formation and stability of bubbles that form during the 

precipitation of cerium oxide that results in coating formation on the substrate surface. When 

gelatin is not present in the deposition solution the bubbles are unstable, readily forming and 

breaking; when gelatin is present the bubbles are very stable. If no gelatin is added to the 

deposition solution a CeCC with a lot of cracks and areas where the coating was no longer 

present, exposing the underlying substrate, was observed (Figure 16a). Coatings made without 

gelatin in the spray solution do very poorly during salt spray testing, with many pits and tails 

after just a few days (Figure 16b) regardless of any other changes in the overall process. 

Analysis of the films made without gelatin after 5 spray cycles using Auger depth profiling 

indicated that the coatings were ~850 nm thick (Figure 17). Many ceramic thin films exhibit 

cracking and loss of adhesion at thicknesses approaching 1000 nm. In contrast, CeCCs deposited 

with gelatin in the spray solution had very few to no cracks or uncoated areas (Figure 18a) and 

performed well during salt spray testing (Figure 18b). The thickness of films made with gelatin 

after 5 spray cycles was typically in the 350-400 nm range (Figure 19), meaning that the 

deposition rate is significantly lower when gelatin is present in the spray solution. 

23 
 a) b) 

Figure 16. a) Scanning electron micrograph of a CeCC deposited on an Al 2024-T3 panel with 

no gelatin in the spray solution; b) optical image of panel after 2 days of salt spray testing. 

0

10

20

30

40

50

60

70

80

0 200 400 600 800 1000 1200

Depth (nm)

Atomic Percent

Al

Figure 17. Auger depth profile of a 5 spray cycle CeCC deposited on an Al 2024-T3 panel with 

no gelatin in the spray solution. 

Ce

O

850 nm

24 
 

 a) b) 

Figure 18. a) Scanning electron micrograph of a CeCC deposited on an Al 2024-T3 panel with 

3200 ppm gelatin in the spray solution; b) optical image of panel after 7 days of salt spray 

testing. 

0

10

20

30

40

50

60

70

80

0 100 200 300 400 500 600 700 800 900

Depth (nm)

Atomic Percent

Al

Ce

O

375 nm

Figure 19. Auger depth profile of a 5 spray cycle CeCC deposited on an Al 2024-T3 panel with 

3200 ppm gelatin in the spray solution. 

25 
Electrochemical impedance characterization of films made without (0 ppm) and with 3200 ppm 

of gelatin in solution indicated that the impedance of the CeCC was significantly higher for the 

films made with gelatin (>100 kΩ-cm2

) than those without gelatin (~50 kΩ-cm

2

, Figure 20). 

This correlated very well with the corrosion testing, as films with higher impedance performed 

better during salt spray exposure. 

0

5000

10000

15000

20000

25000

30000

35000

40000

45000

0 10000 20000 30000 40000 50000 60000 70000 80000 90000

Z' (Ω-cm2)

Z" (

Ω-cm2

)

3200 ppm 

0 ppm 

Figure 20. Electrochemical impedance of CeCC deposited on an Al 2024-T3 panel with 3200 

ppm and no gelatin (0 ppm) in the spray solution. 

Post-Treatment

The formation of cerium phosphate during post treatment greatly improves the corrosion 

protection of CeCCs on Al substrate. Investigations to determine the influence of post treatment 

parameters on corrosion performance were conducted to understand the improvement. The 

initial study focused on the use of different phosphate sources for the post treatment solution. 

Included in the study were orthophosphates (PO4), pyrophosphates (P2O7), and polyphosphates 

(P3O10), along with as deposited (unsealed) CeCCs for comparison. SEM and optical images of 

specimens that were as deposited and post treated in a PO4 solution (Figure 21), and post treated 

in a P2O7 solution (Figure 22) indicate the differences possible using different phosphate sources. 

It was determined that the PO4 based solutions had the fewest cracks in the films, performed the 

best in salt spray, and had the highest electrochemical impedance values (Figure 23). The 

presence of a hydrated CePO4 phase after post treatment (Figure 24) correlated strongly with 

good corrosion performance during salt spray testing. 

26 
 a) b) 

Figure 21. a) Scanning electron micrograph of an as deposited (unsealed) CeCC on an Al 2024-

T3 panel; b) optical image of panel after 14 days of salt spray testing. 

 a) b) 

Figure 22. a) Scanning electron micrograph of a CeCC post treated in a NH4H2PO4 solution at 

85oC for 5 minutes on an Al 2024-T3 panel; b) optical image of panel after 14 days of salt spray 

testing. 

27 
Figure 23. Electrochemical impedance of CeCCs on Al 2024-T3 panels post treated in different 

phosphate solutions. 

Figure 24. X-ray diffraction patterns of CeCCs post treated in different phosphate solutions, and 

one not post treated (unsealed), on Al 2024-T3 panels. 

28 
A summary of the phosphate sealing studies is presented in Table II. Corrosion performance was 

qualitatively evaluated by assigning a ranking to each condition. In Table II 5 dots corresponds 

to passing 2 weeks of ASTM B117 salt spray testing, 3 dots corresponds to passing 1 week of 

ASTM B117, and 1 dot is failure after 1 day of salt spray testing; 2 and 4 dots correspond to 

conditions that fall between those values. The electrochemical testing of the panels correlated 

very well with the other characterization methods. In general, higher charge transfer resistance, 

Rct, lower corrosion current density, icorr, and more positive pitting potentials, Epit, were 

associated with panels that were found to have formed CePO4, had fine cracks, and performed 

best during salt spray testing. 

Table II - Summary of CeCC Phosphate Sealing Study

Rct (kΩ-cm2) icorr (μA/cm2) Epit (mV) CePO4 

Formed

Morphology 

(Cracks)

Corrosion 

Performance

8 1.50 -435 No Large ••

NH4H2PO4 (2.5 wt%) 60 0.60 -261 Yes Fine •••••

Na3PO4 (2.5 wt%) 51 0.45 -280 Yes Fine •••••

K4P2O7 (2.5 wt%) 25 0.74 -275 No Fine ••••

Na2H2P2O7 (2.5 wt%) 15 1.17 -322 No Defects •••

Na5P3O10 (2.5 wt%) 4 2.14 -343 No Defects •

10 sec (85 °C) 17 1.41 -401 No Large ••

30 sec (85 °C) 25 1.98 -340 No Fine •••

2 min (85 °C) 52 0.84 -329 Yes Fine ••••

10 min (85 °C) 62 1.00 -245 Yes Fine •••••

55 °C (5 min) 49 0.83 -384 No Large ••

70 °C (5 min) 63 0.66 -320 Yes Fine ••••

85 °C (5 min) 91 0.65 -258 Yes Fine •••••

Source Time Temp.

Conditions

Unsealed

Deposition Methods

Brush Application

During the last year of the project, work was done to determine the feasibility of depositing a 

CeCC onto Al 2024-T3 substrates using a standard paint brush application. This process could 

be used for field repairs and other locations where a spray booth, immersion tank, or electrolytic 

bath were not available. The same solution was used to deposit CeCCs by spray and brush 

methods in order to compare the application methods. Using similar substrate cleaning 

processes, it was found that a uniform CeCC could be deposited using either a spray or brush 

application method. The brush samples were done by immersing the paint brush into the CeCC 

sample and swabbing it across the surface for a few seconds, waiting ~30 seconds, and reapplying CeCC solution with the brush up to 7 times. In all cases it was possible to obtain a 

CeCC using a brush application method. A plot of spray and brush applied CeCC thicknesses as 

a function of deposition cycles is presented in Figure 25. The spray application resulted in a 

thicker coating per deposition cycle than the brush application but the thicknesses were in the 

range of ~250 to 400 nm that had previously been demonstrated to provide corrosion protection 

during salt spray testing. 

29 
0

50

100

150

200

250

300

350

400

450

500

012345678

Cycles

Coating Thickness (nm)

Brush

Spray

Figure 25. Coating thickness as a function of the number of brush or spray deposition cycles. 

X-ray diffraction analysis of brush and spray applied CeCCs coatings after post treatment 

indicated that the 3, 5, and 7 deposition cycle brush coatings did not have peaks associated with 

hydrated CePO4 as compared to the spray 3 and 5 cycle samples that did have CePO4 peaks 

(Figure 26). Corrosion performance of brush panels during salt spray testing was similar to, but 

not quite as good as, the spray panels. It was not determined why the brush deposited CeCCs did 

not transform into CePO4 during post treatment but does reinforce the importance of deposition 

conditions on the structure and performance of cerium-based corrosion coatings. 

3 Brush

5 Brush

7 Brush

3 Spray

5 Spray

CePO4 hydrate

CeO2

Aluminum

10 20 30 40 50 60 70 80 90

2Θ angle (degrees)

Intensity

3 Brush

5 Brush

7 Brush

3 Spray

5 Spray

CePO4 hydrate

CeO2

Aluminum

10 20 30 40 50 60 70 80 90

2Θ angle (degrees)

Intensity

Figure 26. XRD spectra for coatings deposited using three, five, and seven brush cycles, and 

three and five spray cycles. 

30 
Deposition Mechanism

Based on all of the data available and experimental observations, a mechanism describing what 

is thought to occur during deposition (precipitation) of CeCCs on high strength Al alloys was 

developed. Although it can’t be shown interactively in this document as it is a step-wise 

mechanism, the two major components of the mechanism are shown in Figures 27 and 28. 

Figure 27 shows an increase in pH associated with electrochemical reactions involving the alloy 

substrate that contains cathodic (intermetallic compounds) and anodic (Al matrix) sites. 

Reactions that increase the pH of the solution near the Al/solution interface drive the 

precipitation reactions, including peroxide decomposition, generation of water, and consumption 

of H+. The actual precipitation reactions in the region of higher pH (> 4.5) can involve cerium 

hydroxide or peroxide species depending on the local conditions (Figure 28). In either case these 

can decompose into hydrated cerium oxide or cerium hydroxide phases. The corrosion 

performance of the films is much better after phosphate post treatment (“sealing”), so conversion 

into phosphates is usually done. Whether or not the cerium oxide/peroxide species present after 

deposition can affect the phosphating process is not fully understood and requires more study. 

Figure 27. Schematic drawing of reactions that increase the pH near the surface of Al substrates 

that causes cerium precipitation from solution. 

31 
Figure 28. Schematic drawing of reactions that occur during CeCC precipitation from solution. 

Characterization

Sub-Surface Crevices

During calendar year 2008 Missouri S&T installed and began operation of a FEI Nanolab 600 

focused ion beam (FIB) scanning electron microscope. The FIB is able to selectively remove 

material from specific sites on a sample, enabling cross sectional views at and just below the 

surface of the specimen. Shown in Figure 29 is a low magnification image of a sample after 

removing ~20 μm long, ~10 μm deep section from a CeCC on an Al 2024-T3 substrate 

(essentially looking down into a hole dug out from the surface). Shown in Figure 30 is a cross 

section image of an Al 2024-T3 panel after acid activation cleaning, with no CeCC present. The 

figure shows that the Al 2024 substrate is continuous and without any sub-surface damage prior 

to CeCC deposition. 

32 
CeCC 

Al 2024 

Figure 29. Electron micrograph image of a CeCC on an Al 2024-T3 panel after FIB sectioning. 

Pt Protection Layer 

Surface 

Al 2024-T3 Substrate 

Figure 30. Cross sectional micrograph image of an Al 2024-T3 panel after acid activation 

cleaning (no sub-surface crevices). 

Presented in Figure 31 is a FIB cross sectional image of samples after spray deposition of CeCC 

onto cleaned Al 2024-T3 substrates. The areas examined were near the large cracks in the 

CeCC, ~10% of the total surface area on a sample (90% have fine or small cracks). It was 

observed that the Al 2024-T3 substrate under the CeCC with large cracks had sub-surface 

crevices, an indication that the Al substrate had been preferentially etched and material removed 

during deposition. The crevices can be near the surface only or extend down into the substrate 

33 
several micrometers. It should be noted that the areas with fine cracks (90% of total surface 

area) do not have the sub-surface crevices and look similar to Figure 30. 

CeCC 

Sub-surface crevices 

Figure 31. Cross sectional micrograph image of an Al 2024-T3 panel after CeCC deposition 

(contains sub-surface crevices). 

To investigate the origin of the sub-surface crevices a solution consisting of H2O2 and NaCl was 

made to simulate the H2O2 plus CeCl3 solution used to deposit CeCCs. Without the presence of 

Ce in the solution there is no film deposited but the active etching species, Cl-

 and H2O2, are still 

present. As seen in Figure 32 below, the sub-surface crevices were observed after spraying the 

salt plus peroxide solution on the surface of a cleaned Al 2024-T3 panel. Therefore, the 

concentration of the chloride and hydrogen peroxide in the CeCC spray solution is sufficient to 

preferentially etch the Al 2024-T3 substrate. Studies were conducted that demonstrated the 

reducing the amount of Cl- and H2O2 in the deposition solution reduced, or eliminated, the 

formation of sub-surface crevices. However, samples without sub-surface crevices did not 

perform well during corrosion testing. 

34 
Figure 32. Cross sectional micrograph image of an Al 2024-T3 panel after spraying a H2O2 + 

NaCl solution on the surface. 

Post Salt Spray Surface Analysis

Characterization of CeCC panels before and after salt spray testing was done throughout the 

project. Panels that passed the 14 day visual inspection criteria after salt spray testing were 

analyzed to see if differences in material composition or structure could be measured. Cross 

sectional transmission electron microscopy (TEM) of the phosphate sealed CeCC coating before 

salt spray exposure indicated that the film was a dense, continuous coating that was a few 

hundred nanometers in thickness (Figure 33a). After 14 days in the salt spray cabinet the CeCC 

was still present but an additional layer was present on the surface of the CeCC (Figure 33b). 

Additional analysis of the panels using depth profiling revealed that the CeCC before salt spray 

testing was a mixture of Ce, O, and P (Figure 34a) but after salt spray exposure Al and O were 

present on top of the CeCC (Figure 34b). The presence of an oxide layer on top of the CeCC 

after salt spray testing was detected on multiple samples throughout the project. Collectively, the 

TEM and AES results show that an aluminum oxide layer was present on the surface of the 

CeCC after 14 days of salt spray exposure on panels that passed 336 hours of testing. 

a) 

35 
b) 

Figure 33. Cross-sectional TEM images of cerium based conversion coatings: a) as-deposited, b) 

after 14 days of salt spray testing. 

0 100 200 300 400

0

25

50

75

100

ATOMIC %

SPUTTER DEPTH (nm)

O

Al

Ce

P

0 200 400 600 800

0

25

50

75

100

Ce

O

Al

ATOMIC %

SPUTTER DEPTH (nm)

P

a) b) 

Figure 34. Auger electron spectroscopy depth profiles of cerium based conversion coatings: a) 

as-deposited and b) after 14 days of salt spray testing. 

5.3 Multifunctional UV (MUV) Curable Coatings 

Development and evaluation of MUV coatings was done throughout the project. A total of 5 

rounds of experimental testing were conducted. Within the first few months of the project it was 

decided that each round of testing would use commercially available chromate and non-chromate 

coatings as controls. This was done in order to compare results from military approved coatings 

to the ones being developed and tested in this project. A brief overview of the 5 rounds (rds) of 

testing is presented in Table III. The detailed results from the testing are available from the 

project Principal Investigator. 

36 
Table III - Summary of MUV Testing

• Completed 5 Rounds of MUV Test and Evaluation on A1 2024 and 

A1 7075 Substrates 

3⁄4 Chromate & Non-Chromate Controls As Reference 

(CrCC/TCP, Epoxy Primer, Polyurethane Top Coat) 

3⁄4 MUV on CrCC, CeCC, TCP and Bare A1 2024-T3 

3⁄4 B117 Salt Spray, SO2 Exposure, Filiform, Cross Hatch Adhesion, 

Skydrol Resistance, GE Impact, Low Temp Mandrel, Accelerated 

UV Weathering 

• Rd 1 (FY06) – Drawbar MUV, 2 Corrosion Inhibitors Evaluated 

• Rd 2 (FY07 – Drawbar MUV, 3 Corrosion Inhibitors Evaluated 

• Rd 3 (FY08) – Spray MUV, Wayne Pigment Inhibitor 

• Rd 4 (FY08/09) – Spray MUV, Wayne, Different Formulations 

• Also Evaluated Gloss White 

• Rd 5 (FY09) – Spray MUV, Wayne, Flexibility Adjustments 

Round 1 MUV Evaluations

Round 1 testing was limited to salt spray testing only of MUV coatings with Hybricor 204 or 

Deft corrosion inhibitor on chromate and cerium coated Al 2024-T3 or Al 7075-T6 panels. 

Commercial chromate and non-chromate coating were used as controls. The controls were spray 

applied at Boeing and the MUV coatings were drawbar applied at LCC. The MUV coatings with 

Hybricor 204 inhibitor performed as well as or better than the controls in terms of preventing 

salting in the scribe after 3000 hours of testing. Shown in Figure 35 are some of the panels after 

3000 hours testing, with the Hybricor 204 MUV coated panels on CrCC and CeCC having no 

visible salting in the scribe. This result was very significant as it demonstrated that a UV curable 

formulation loaded with corrosion inhibitors has the capability of protecting against corrosion of 

scribed high strength aluminum panels on chromate and non-chromate conversion coatings. 

37 
 Chromate Control Non-Chromate Control 

 Deft MUV on CrCC Deft MUV on CeCC 

 Hybricor 204 MUV on CrCC Hybricor 204 MUV on CeCC 

Figure 35. Optical images of Stage 1 Al 2024-T3 coated panels after 3000 hours of neutral salt 

spray testing. 

38 
The MUV coatings were stripped off some of the panels following 3000 hours of salt spray 

testing to determine if corrosion under the coating had occurred. As shown in Figure 36 the 

surface and scribe of the Al had no visible corrosion or staining for the Hybricor 204 panels 

while the Deft MUV and control panels each had corrosion by-product in and around the scribe. 

 Chromate Control Non-Chromate Control 

 Deft MUV on CrCC Deft MUV on CeCC 

 Hybricor 204 MUV on CrCC Hybricor 204 MUV on CeCC 

Figure 36. Optical images of Stage 1 Al 2024-T3 coated panels after 3000 hours of neutral salt 

spray testing and removal of the corrosion coatings. 

39 
Characterization of the MUV stripped Hybricor 204 panels using mapping Auger spectroscopy 

was done to determine what, if any, differences between the panels could be detected. Panels 

which were coated, scribed, and then stripped, but not subjected to salt spray testing, were used 

as control panels for comparison of “before” and “after” salt spray testing. Shown in Figure 37 

is Auger maps with the percentage of Al, Cr, and Zn measured near the scribe for Hybricor 

panels on a CrCC before and after salt spray testing. Zinc is one of the components of the 

Hybricor 204 compound. The scribe runs vertically down the middle in all cases; it is clearly 

demarked for the Cr and Ce signal maps with no salt spray exposure as the blue strip. The data 

indicate that corrosion protection of the Al substrate and scribe is related to the corrosion 

inhibitor from the MUV, in this case indicated by the presence of Zn on the panel. There was no 

Cr found in the scribe and Zn was not found in the scribe or on the surface before testing. After 

3000 hours of salt spray testing, Zn was detected in the scribe and on the surface of the Al 

substrate, a strong indication that the corrosion inhibitor in MUV migrated and protected the 

panel. Similar results were found for Hybricor 204 panels that passed 3000 hours of ASTM 

B117 testing on CeCC (Figure 38), additional support that the MUV was actively protecting the 

Al against corrosion. 

40 
 Cr Signal: No salt spray Cr Signal: After Passing 3000 hours 

20% 21% 0.5% 

19% 20% 0.1% 

 

 Al Signal: No salt spray Al Signal: After Passing 3000 hours 

2% 28% 4% 

3% 40% 6% 

 Zn Signal: No salt spray Zn Signal: After Passing 3000 hours 

<1% 

<1% <1% 3% 5% 2% 3% 2% 

Figure 37. Auger maps for Cr, Al, and Zn near the scribe for two different Hybricor 204 MUV 

coated panels; one not exposed to salt spray and the other after passing 3000 hours salt spray. 

41 
 Ce Signal: No salt spray Ce Signal: After Passing 3000 hours 

37% 34% 3% 

45% 35% 30% 2% 22% 

 Al Signal: No salt spray Al Signal: After Passing 3000 hours 

8% 4% 36% 

2% 29% 3% 

 Zn Signal: No salt spray Zn Signal: After Passing 3000 hours 

<1% <1% <1% 

3% 1% 2% 

2% 4% 

Figure 38. Auger maps for Ce, Al, and Zn near the scribe for two different Hybricor 204 MUV 

coated panels; one not exposed to salt spray and the other after passing 3000 hours salt spray. 

42 
Round 2 MUV Evaluations

Based on the promising results of Round 1 testing, a more complete set of tests was conducted 

on MUV coatings during Round 2, including filiform, adhesion, fuel resistance, SO2 spray, and 

Xe arc weathering in addition to the neutral salt spray testing. Multifunctional UV coatings were 

applied to CrCC, CeCC, tri-valent chromium (TCP), and bare Al 2024-T3 panels, and chromate 

and non-chromate panels were again used as controls. Hybricor 204, Deft, HT-13, and HT-20 

corrosion inhibitors, as well as different monomers, were evaluated. The experimental matrix 

was exploratory in nature such that the test results were expected to vary widely. This approach 

was taken to help identify and optimize the key performance variables in the MUV coating 

system. In general, the MUV coatings with Hybricor 204 corrosion inhibitor and IBOA 

monomer on CrCC performed better than other MUV inhibitor, monomer, and conversion 

coating systems, but not as well as the chromate controls. In most cases the MUV coating 

systems with Hybricor 204 inhibitor on CrCC were close to passing all of the performance 

requirements. The results were considered encouraging but not definitive. Shown in Figure 39 

are the chromate and non-chromate Al 2024-T3 control panels after salt spray testing along with 

Hybricor 204 loaded MUV coatings on CrCC and CeCC Al 2024-T3 panels. 

 Chromate Control Non-Chromate Control 

 Hybricor 204 MUV on CrCC Hybricor 204 MUV on CeCC 

Figure 39. Optical images of Round 2 Al 2024-T3 coated panels after 2000 hours of neutral salt 

spray testing. 

43 
In response to a SERDP action item, results from salt spray testing of MUV coatings with 

Hybricor 204 on TCP and bare Al 2024-T3 are presented in Figures 40 and 41. The TCP 

conversion coatings with a Hybricor 204 loaded MUV (Figure 40) looked similar to the CeCC 

results with a little salting in the scribes but the MUV in direct contact with the Al substrate had 

numerous blisters and significant salting in the scribe (Figure 41). 

Figure 40. Optical image of a Round 2 Hybricor 204 MUV coated Al 2024-T3 panel with a TCP 

conversion coating after 2000 hours salt spray. 

Figure 41. Optical image of a Round 2 Hybricor 204 MUV coated Al 2024-T3 panel that did not 

have a conversion coating (bare) after 2000 hours salt spray. 

44 
Filiform corrosion testing was conducted on Alclad 2024-T3 substrates (i.e. Al roll bonded to Al 

2024-T3) out to 1000 hours of testing. Figure 42 depicts the control, HT-13 MUV, and Hybricor 

204 MUV panels after filiform testing. Chrome and chrome-free controls passed filiform testing 

as did the Hybricor 204 on CrCC as all corrosion was less than 1/4” from the scribe and most 

were less than 1/8” away from the scribe. The corrosion away from the scribe for the HT-13 

MUV panels after filiform testing was just outside the test specifications, as was also the case for 

the CeCC panels with MUV coatings. These results were considered promising for a first 

attempt. 

 Chromate control Non-chromate control 

 MUV with HT-13 Inhibitor MUV with Hybricor 204 

Figure 42. Images of integrated coatings on CrCC Al clad Al 2024-T3 after 1000 hours of 

filiform corrosion testing. 

45 
Ladder Studies between Round 2 and Round 3

y 

e 

r 

Al 

f 

 charge level was chosen for 

bsequent work to develop a MUV spray deposition process. 

Multifunctional UV curable coatings applied by drawbar (draw-downs) resulted in Hybricor 204

corrosion inhibitor from Wayne Pigments demonstrating the best performance during salt spra

testing of scribed Al 2024-T3 panels with chromate conversion coatings (CrCC). The initial 

work used a ~36 wt% charge level of the Hybricor 204, and ladder studies indicated that charg

levels near 30% were also effective at prevent salting of scribe lines during salt spray testing. 

Additional ladder studies were then conducted at charge levels of 36.4%, 34.6%, 32.8%, 30.9%, 

29.1%, and 27.3% to determine the optimum value, as lowering the charge level improves othe

properties such as flexibility. All of the MUV coatings in the study were applied to CrCC 

2024 substrates using a drawbar. Other than samples that had adhesion failures related to 

substrate preparation, each of the charge levels had a panel with 1,A ratings after 3000 hours o

ASTM B117 testing. Images of the panels after 3000 hours of salt spray testing are shown in

Figure 43. Taking into account a number of factors, the 29.1%

su

 36.4% Charge Level 34.6% Charge Level 32.8% Charge Level 

 30.9% Charge Level 29.1% Charge Level 27.3% Charge Level 

rent charge levels of 

ybricor 204 corrosion inhibitor after 3000 hours of salt spray testing. 

Figure 43. Optical images of MUV coated Al 2024-T3 panels with diffe

H

46 
Round 3 MUV Evaluations

onding 

e 

nd an 

uble rubs, and good appearance with 20° gloss = 0.5, 60° gloss = 4.3, and 

5° gloss = 7.6. 

UV 

repared. A listing of the panels tested and coatings 

sed in the study are presented in Table IV. 

Table IV - Coating Systems Evaluated (Round 3)

After determining the amount of Hybricor 204 corrosion inhibitor to use in the MUV, 

efforts were then focused on developing a MUV formulation that could be spray applied. It 

was found that the gloss values for sprayed panels were higher than those for corresp

draw-downs, so formulation adjustments were made to lower gloss and to improve 

sprayability, flow, and appearance. A study of additional dispersing aids for the Hybricor 

204 corrosion inhibitor indicated that lower viscosity and better coating sprayability could 

be obtained with Solsperse hyperdispersants. The best results were obtained with Solspers

39000, which was incorporated into the formulation. Adjustments were also made to the 

photoinitiator blend, monomer blend, oligomer, and level of filler used. A different black 

pigment was incorporated along with an improved package for stable weatherability a

additive for improved flow. The modified MUV coating on CrCC aluminum panels 

exhibited 5B adhesion (100%), reverse impact strength flexibility of 14 inch-lbs, resistance 

to >200 MEK do

8

After adjustments to the MUV formulation had been made, coatings were applied to Al 2024-T3 

and Al 7075-T6 substrates with CrCC, CeCC, and TCP using the modified low gloss gray M

coating sprayed onto the panels. Chromate and non-chromate coated control panels using 

commercially available materials were also p

u

Panel ID Pretreatment Coating system 

A 

MIL-C-5541/PS13209 and Thin 

P

dichrom ibility 

panels only) 

Chromate conversion coating, MUV (Hybricor 204) 

film sulfuric acid anodized per 

S 13201 TY II with 2 minute

ate seal (flex

B CeCC MUV (Hybricor 204) 

C TCP 

PPG CA8211/F36375/CA8200B top 

Deft 65GN015 primer, 

coat(chrome free control) 

D 

MIL-C-5541/PS13209 and Thin 

P

dichrom ibility 

panels only) 

CA8211/F36375/CA8200B (chromated 

control) 

Chromate conversion coating, 

film sulfuric acid anodized per 

S 13201 TY II with 2 minute

ate seal (flex

Deft 44GN072 primter, PPG 

47 
Chromate conversion coated panels had good appearance but the appearance of the coa

on cerium conversion coa

ting 

ted panels was not as good, with some wrinkling at higher coating 

icknesses (Figure 44). Appearance was better on Alclad panels which had a lighter 

erium conversion coat. 

 in 

also 

0 

l loss of less than 5 at 60° and a delta E of less than 1. The MUV 

coatings had gloss values of ~2, meeting the specification, but the delta E values were close to 5, 

well above the requirement. 

th

c

Cerium conversion coating Cerium conversion coating Chromate conversion coating 

Figure 44. Optical images of MUV coated Al 2024-T3 panels on CeCC and CrCC pretreatments. 

After the panels were prepared, evaluation was conducted at Boeing. The wet tape adhesion tests

indicated that the MUV and chromate primer on CrCC passed with images of the panels shown

Figure 45. Exposure of the panels to Skydrol fluid for thirty days and measurement of the pencil 

hardness resulted in only the chromate control panels passing the test. All of the other coating 

combinations failed, with complete loss of adhesion occurring for MUV spray coatings on CeCC. 

Exposure of panels to xenon-arc radiation for 1000 hours as an accelerated weathering test was 

conducted. Measurement of the changes in optical appearance and color were recorded at the 50

and 1000 hour mark. The results indicated that the chromate and non-chromate control panels 

passed the test, with a spectra

48 
 MUV on CrCC MUV on CeCC 

 Non-chrome primer on TCP Chromate primer on CrCC 

Figure 45. Optical images of wet scribe test results. 

Filiform corrosion for 1000 hours on Alclad 2024-T3 and Alclad 7075-T6 substrates was 

performed. The chromate control panels for both 2024 and 7075 passed the test while the nonchromate controls passed on 2024 but failed on 7075, with the MUV coatings on CrCC and 

CeCC failing on both substrates. 

Neutral salt spray testing of control and MUV coated CrCC, CeCC, and TCP pretreatments on 

Al 2024-T3 and Al 7075-T6 panels was done out to 3000 hours with ratings assessed every 1000 

hours. The chromate and non-chromate controls performed the best, with 1,A or 2,A ratings, 

with the MUV on CrCC (2,4,A) ratings next best. The MUV coatings on TCP and CeCC had the 

lowest rankings (2,4,9,H typical). Pictures of the panels after 3000 hours of ASTM B117 testing 

are presented in Figures 46-48. 

49 
Chromate Primer on CrCC 

Non-chromate Primer on TCP 

Figure 46. Optical images of Al 2024-T3 control panels after 3000 hours of salt spray corrosion 

testing. 

50 
MUV on CrCC 

MUV on CeCC 

Figure 47. Optical images of MUV coated Al 2024-T3 panels with CrCC and CeCC 

pretreatments after 3000 hours of salt spray corrosion testing. 

51 
MUV on TCP 

Figure 48. Optical images of MUV coated Al 2024-T3 panels with TCP pretreatments after 3000 

hours of salt spray corrosion testing. 

52 
Overall the performance of the coatings was not as good on Al 7075-T6 panels as the Al 2024-

T3 panels, with no coating systems rated 1,A after 3000 hours. The chromate and non-chromate 

control ratings were ~2,4,A as were the MUV on CrCC panels. The MUV on CeCC had a rating 

of ~3,5,9,H. The MUV on CrCC was given the #1 rank after 3000 hours. Figures 49 and 50 are 

images of the panels after salt spray testing. 

Chromate Primer on CrCC 

Non-chromate Primer on TCP 

Figure 49. Optical images of Al 7075-T6 control panels after 3000 hours of salt spray corrosion 

testing. 

53 
MUV on CrCC 

MUV on CeCC 

Figure 50. Optical images of MUV coated Al 7075-T6 panels with CrCC and CeCC 

pretreatments after 3000 hours of salt spray corrosion testing. 

54 
MUV Coated CeCC Studies

The results from the Round 3 testing clearly indicated that improvement in the salt spray 

performance of the MUV on CeCC was needed. A test matrix of CeCCs deposited under 

different conditions that were then sprayed with the same formulation of MUV was carried out. 

Salt spray testing was done out to 2000 hours. The results were encouraging as a few panels had 

1,A ratings while most of the panels had 1 ratings in combination with blisters (rating 8). The 

heat treated and fluoroboric acid cleaned Al 2024-T3 samples did well as did the fluoroboric acid 

cleaned Al 7075-T6 substrates. Blistering under the MUV coating was a common flaw for all 

conditions. 

In October 2008 all of the team members met at the Light Curable Coatings (LCC) facility in 

Berea, OH to process and coat panels (Table V). This was done in order to investigate how 

depositing the CeCC and then MUV coating within minutes of each operation affected coating 

performance. In addition to the CeCC samples made at LCC, CeCC panels were also made in 

Rolla the day before the trip so that a comparison could be made. All samples were MUV coated 

and cured at LCC. The CeCCs made at LCC were blow dried with air for 5 minutes before the 

MUV coating was spray deposited. Among the CeCC variables investigated were the number of 

spray cycles, post treatment sealing temperature, and cleaning/surface preparation process. In 

some cases the MUV was sprayed directly onto the cleaned panel without a conversion coating. 

Table V - Test Matrix for MUV/CeCC Panels Done at LCC Oct 2008

Condition Alloy Surface Prep. Coating Post Treatment Notes Panel Numbers

1 2024 standard 3 sprays 55 C 1-(1-3)

1R 2024 standard 3 sprays 55 C sprayed at MST 1R-(1-6)

2 2024 standard 3 sprays 85 C 2-(1-6)

2R 2024 standard 3 sprays 85 C 2R-(1-6)

2A 2024 standard 3 sprays 85 C pH 2A-(1-3)

2B 2024 standard 3 sprays 85 C dry overnight 2B-(1-6)

3 2024 standard 1 spray 85 C 3-(1-6)

3A 2024 standard 1 spray 85 C pH 3A-(1-3)

3B 2024 standard 1 spray 85 C dry overnight 3B-(1-6)

4 2024 standard 5 sprays 85 C 4-(1-6)

4A 2024 standard 5 sprays 85 C pH 4A-(1-3)

4B 2024 standard 5 sprays 85 C dry overnight 4B-(1-3)

5 2024 turco only no Ce coating N/A 5-(1-6)

5R 2024 turco only no Ce coating N/A sprayed at MST 5R-(1-6)

6 2024 turco and acid no Ce coating N/A 6-(1-6)

6R 2024 turco and acid no Ce coating N/A sprayed at MST 6R-(1-6)

7 2024 standard brush (1 stroke) 85 C 7-(1-6)

7R 2024 standard brush (1 stroke) 85 C brushed at MST 7R-(1-6)

8 2024 standard wipe (1 stroke) 85 C 8-(1-6)

8R 2024 standard wipe (1 stroke) 85 C brushed at MST 8R-(1-6)

9 2024 standard 5 sprays 85 C UV treatment before MUV application 9-(1-6)

9A 2024 standard 5 sprays not sealed UV treatment before MUV application 9A-(1-6)

10 2024 Cu seeding 3 sprays 85 C 10-(1-6)

10R 2024 Cu seeding 3 sprays 85 C sprayed at MST 10R-(1-6)

11 7075 Cu seeding 3 sprays 85 C 11-(1-6)

11R 7075 Cu seeding 3 sprays 85 C sprayed at MST 11R-(1-6)

12 2024 Luna no Ce coating 85 C 12-(1-5)

12R 2024 Luna no Ce coating 85 C prepared at MST 1x3 12R-(1-6)

13 7075 standard 3 sprays 85 C 13-(1-6)

13 R 7075 standard 3 sprays 85 C sprayed at MST 13R-(1-6)

55 
Presented in Table VI are some of the results from evaluation of the MUV/CeCC panels done at 

LCC. Most of the test conditions on Al 2024-T3 substrates resulted in adequate pencil hardness 

values (>H), reasonable adhesion ratings (>4B), 60° gloss values <5, greater than 200 MEK rubs 

without coating removal, and maintaining integrity after 24 hour Skydrol fluid exposure. The 

panels that did not do as well were related to using a lower temperature (55°C) post treatment 

step, a thicker CeCC layer (5 spray cycles), and brush or wipe application of the CeCC. Data 

from MUV on bare Al 2024-T3 substrates (no conversion coating) were comparable to the 

results from the panels with a CeCC. The results on Al 7075-T6 panels (condition 13) were poor 

in almost all cases. 

Table VI - Pencil Hardness, Adhesion, Gloss, MEK Rub and Skydrol Results

for MUV/CeCC Panels Done at LCC Oct 2008

PENCIL GLOSS 24 HR 

CONDITION/PANEL HARDNESS ADHESION

200 600

850 MEK RUBS SKYDROL

CONDITION 1-3 F 0B 0.6 5.0 9.6 60 RUBS FAILED 

CONDITION 1R-5 4H 3B 0.5 3.6 7.9 >200 RUBS PASSED 

CONDITION 2-6 4H 3B 0.5 3.8 7.8 >200 RUBS PASSED 

CONDITION 2R-1 3H 4B 0.7 5.4 11.3 >200 RUBS PASSED 

CONDITION 2A-1 2H 3B 0.5 3.7 7.9 >200 RUBS PASSED 

CONDITION 2B-4 F 3B 0.6 4.6 9.5 >200 RUBS PASSED 

CONDITION 3-1 4H 5B 0.6 5.1 12.7 >200 RUBS PASSED 

CONDITION 3A-3 4H 4B 0.5 3.8 8.7 >200 RUBS PASSED 

CONDITION 3B-2 4H 4B 0.5 4.5 8.8 >200 RUBS PASSED 

CONDITION 4-3 F 1B 0.5 3.6 8.9 >200 RUBS PASSED 

CONDITION 4A-3 H 2B 0.5 3.6 7.6 >200 RUBS PASSED 

CONDITION 4B-3 2H 2B 0.5 4.5 9.7 >200 RUBS PASSED 

CONDITION 5-1 3H 3B 0.6 4.6 9.4 >200 RUBS PASSED 

CONDITION 5R-1 4H 4B 0.5 4.3 8.0 >200 RUBS PASSED 

CONDITION 6-1 4H 5B 0.5 4.1 8.2 >200 RUBS PASSED 

CONDITION 6R-1 4H 5B 0.5 4.4 9.5 >200 RUBS PASSED 

CONDITION 7-1 4H 2B 0.5 4.4 11.3 195 RUBS PASSED 

CONDITION 7R-1 4H 5B 0.5 4.1 9.2 >200 RUBS PASSED 

CONDITION 8-1 4H 2B 0.5 4.4 8.4 >200 RUBS PASSED 

CONDITION 8R-1 3H 1B 0.7 5.6 11.6 190 RUBS PASSED 

CONDITION 9-3 4H 5B 0.6 4.4 8.2 >200 RUBS PASSED 

CONDITION 9A-2 2H 4B 0.4 3.6 9.3 >200 RUBS PASSED 

CONDITION 10-1 4H 5B 0.6 4.5 8.2 >200 RUBS PASSED 

CONDITION 10R-1 4H 5B 0.6 5.2 10.8 >200 RUBS PASSED 

CONDITION 11-3 4H 3B 0.6 4.6 11.3 >200 RUBS PASSED 

CONDITION 11R 4H 5B 0.6 5.0 10.3 >200 RUBS PASSED 

CONDITION 12-3 4H 4B 0.4 3.3 7.6 >200 RUBS PASSED 

CONDITION 12R-1 F 4B 0.6 4.8 10.1 145 RUBS FAILED 

CONDITION 13-4 2H 0B 0.6 4.6 11.8 175 RUBS FAILED 

CONDITION 13R-5 2H 0B 0.8 6.3 12.7 98 RUBS FAILED 

Pencil Hardness Scale: 9B<8B<7B<6B<5B<4B<3B<2B<B<HB<F<H<2H<3H<4H<5H<6H<7H<8H<9H

Cross-hatch adhesion percentages: 0B (0% to 35%), 1B (35% to 65%), 2B (65% to 85%), 3B (85% to 95%), 4B (over 95%), 5B (100%) 

56 
Salt spray testing of the MUV/CeCC panels made at LCC was done along with control panels 

of MUV on CrCC (labeled QCCC) and MUV directly on bare Al-2024 T3 substrates. The 

ratings for the panels after 500 and 1000 hours are listed in Table VII. Although the scribe 

lines were still shiny for many of the test panels after 1000 hours of salt spray testing, most of 

the cerium conversion coated panels contained blisters, and the only conditions that had any 

1A ratings after 1000 hours of testing were conditions with no CeCC and one that had UV 

treatment prior to MUV deposition, and the control MUV on QCCC panels. 

Table VII - Salt Spray Ratings for MUV/CeCC Panels Done at LCC Oct 2008

57 
Effect Of CeCC Variables On Corrosion Resistance Of Sprayed MUV Films For MS&T 10/2008 Test Matrix

CONDITION/PANEL Left Top Right Bottom 500 Hrs 1000 Hrs

CONDITION 1-1 1.90 2.00 1.90 2.00 1,14,B 3,6,8,14,H

CONDITION 1-2 2.10 1.70 2.00 2.20 1,4,8,14,G 3,6,8,14,H

CONDITION 1R-1 1.15 1.50 1.45 1.50 1,A 1,4,8,E

CONDITION 1R-2 2.20 2.00 2.30 2.20 1,1,8,B 1,4,8,E

CONDITION 2-4 2.60 2.20 2.10 3.00 1,8,13,B 1,8,13,H

CONDITION 2-5 2.60 2.40 2.20 2.60 1,8,13,B 1,8,13,E

CONDITION 2R-5 1.70 2.10 1.15 2.20 1,8,B 1,8,G

CONDITION 2R-6 1.80 2.30 2.00 1.90 1,A 1,8,B

CONDITION 2A-2 2.10 2.20 2.10 1.80 1,8,13,B 1,8,13,D

CONDITION 2A-3 2.30 2.60 1.90 1.95 1,8,14,B 1,4,8,14,H

CONDITION 2B-1 2.40 1.55 2.40 1.85 1,4,8,13,B 1,4,8,13,H

CONDITION 2B-3 1.95 2.00 2.40 1.85 1,8,13,B 1,8,13,G

CONDITION 3-2 1.70 1.65 1.95 1.70 1,8,B 1,8,F

CONDITION 3-3 1.75 2.10 2.10 2.30 1,8,B 1,8,E

CONDITION 3A-1 2.10 1.70 1.40 2.00 1,8,B 2,5,8,B

CONDITION 3A-2 1.60 1.70 1.75 1.70 1,4,8,C 2,4,8,H

CONDITION 3B-1 2.60 2.50 2.15 2.20 1,4,8,C 1,4,8,13,D

CONDITION 3B-3 1.70 1.85 2.30 1.90 1,8,B 1,4,8,G

CONDITION 4-1 1.75 2.20 1.95 2.30 1,A 2,4,8,D

CONDITION 4-4 1.75 1.75 1.65 1.75 1,13,B 1,13,B

CONDITION 4A-1 1.50 1.80 1.35 1.45 2,4,8,14,B 3,6,8,14,E

CONDITION 4A-2 1.45 1.80 1.60 1.35 2,4,8,13,B 2,4,8,14,B

CONDITION 4B-1 2.40 2.60 2.50 3.00 1,4,8,14,C 1,4,8,14,H

CONDITION 4B-2 2.20 2.20 1.75 1.95 1,4,8,14,B 2,4,8,14,G

CONDITION 5-3 2.60 2.50 2.10 2.60 1,8,B 1,8,G

CONDITION 5-4 2.30 2.10 2.40 2.80 1,4,8,10,B 1,4,8,10,E

CONDITION 5R-5 1.80 2.40 1.75 1.60 1,8,B 1,8,C

CONDITION 5R-6 1.80 2.10 1.55 1.65 1,8,B 1,8,10,C

CONDITION 6-3 1.80 2.20 2.10 1.85 1,A 1,A

CONDITION 6-4 2.40 2.90 3.00 2.50 1,A 1,8,B

CONDITION 6R-2 1.85 2.10 2.20 2.20 1,A 1,A

CONDITION 6R-4 2.20 2.30 2.10 2.40 1,8,B 1,8,C

CONDITION 7-3 1.60 1.60 1.90 1.70 1,8,B 2,4,8,G

CONDITION 7-4 1.50 1.70 2.10 2.20 1,8,B 2,4,8,H

CONDITION 7R-3 1.65 1.55 1.60 1.75 1,8,C 1,8,C

CONDITION 7R-4 1.80 2.00 2.10 1.85 1,8,C 1,8,G

CONDITION 8-3 1.85 1.90 2.50 2.30 1,8,B 1,8,G

CONDITION 8-4 1.55 1.50 1.30 1.35 1,8,B 1,8,G

CONDITION 8R-2 1.90 1.70 1.80 1.60 1,4,8,D 1,4,8,F

CONDITION 8R-3 1.80 2.20 1.60 1.85 1,8,B 1,8,C

CONDITION 9-1 1.65 2.30 2.10 1.85 1,8,B 1,13,B

CONDITION 9-2 1.95 2.10 2.30 2.10 1,8,13,B 1,8,13,F

CONDITION 9A-1 1.75 1.70 1.45 1.20 1,A 1,A

CONDITION 9A-3 2.30 2.30 2.10 2.20 1,8,13,C 1,8,13,F

CONDITION 10-3 2.10 1.75 2.20 1.95 1,8,B 1,8,C

CONDITION 10-4 2.30 2.10 2.20 3.00 1,13,B 1,8,14,H

CONDITION 10R-3 1.70 2.10 2.10 2.40 1,8,B 1,8,C

CONDITION 10R-4 1.65 1.85 1.55 1.30 1,8,B 1,8,C

CONDITION 11-1 2.60 2.80 2.20 2.50 1,4,8,G 2,4,8,H

CONDITION 11-2 2.60 2.90 2.60 3.00 1,4,8,H 2,4,8,10,13,H

CONDITION 11R-2 1.85 2.00 1.60 1.70 1,4,A 2,4,8,C

CONDITION 11R-3 2.30 1.55 1.60 1.65 1,4,A 2,4,8,B

CONDITION 12-4 1.75 1.40 1.40 2.20 1,4,8,C 2,4,8,G

CONDITION 12-5 1.45 1.95 1.65 2.20 1,4,8,10,C 1,4,8,10,F

CONDITION 13-5 2.10 1.70 1.60 1.55 2,4,8,13,C 2,4,8,14,D

CONDITION 13-6 1.80 1.90 1.50 2.00 2,4,8,13,C 2,4,8,14,C

CONDITION 13R-2 2.20 1.95 1.90 2.10 2,4,8,B 2,4,8,C

CONDITION 13R-3 2.40 2.30 1.85 2.40 2,4,8,C 2,4,8,D

CONTROL QCCC-1 1.95 2.00 1.65 2.20 1,A 1,A

CONTROL QCCC-2 1.85 2.20 1.90 2.10 1,A 1,A

CONTROL 2024 BARE-1 2.20 2.00 2.10 2.20 1,8,B 1,8,E

CONTROL 2024 BARE-2 1.75 2.20 1.75 1.90 1,8,B 1,8,E

Initial Film Build (mils) Corrosion Inspection & Scribe Line Ratings

Round 4 MUV Evaluations

For the panels made and evaluated during Round 4 the corrosion inhibitor level was the same as 

Round 3 with changes to the formulation made to adjust the mechanical and physical properties 

of the MUV coating. Results indicated that ASTM B117 neutral salt spray test ratings were 

similar for MUV coatings on CrCC, chromate controls, and non-chromate controls on Al 2024 

and Al 7075 substrates (Figures 51 and 52). Ratings for MUV on TCP on 2024 were ~ 2,A while 

MUV on cerium conversion coatings (CeCC) were ~3,E with many blisters. 

58 
Figure 51. Al 2024-T3 chromate control panels after 3000 hours ASTM B117 testing. 

Figure 52. Al 2024-T3 panels with MUV on CrCC after 3000 hours ASTM B117 testing. 

The MUVs were able to pass 200 MEK rub testing but coatings were unable to retain their 

integrity after a 24 hour Skydrol soak. The chromate and non-chromate controls passed wet tape 

adhesion and room temperature flexibility tests but the MUV coatings on CrCC and CeCC did 

not. Only the chromate controls passed low temperature flexibility tests. Xenon arc weathering 

of the chromate and non-chromate controls were within specifications but the change in the MUV 

coatings optical appearance were outside of the acceptable limits. 

Chromate control and MUV coatings on CrCC passed filiform corrosion testing on Al 2024 and 

Al 7075 substrates. MUV coatings on CeCC passed on Al 7075 while non-chromate controls 

59 
passed on Al 2024. The corrosion performance of MUV coatings was excellent but adjustments 

to the MUV formulations did not improve the non-corrosion properties of the coatings. 

Round 5 MUV Evaluations

Changes in MUV formulation were made to try to improve the physical properties of the MUV 

films from Round 4 while still maintaining corrosion inhibition. After 2000 hours of ASTM 

B117 neutral salt spray testing, the MUV coatings on chromate conversion coated (CrCC) Al 

2024 and Al 7075 substrates had comparable ratings (1, 4, A) with the chromate controls in 

testing done at Boeing and Light Curable Coatings (Figure 53). Small blisters away from the 

scribe were present on the MUV coated panels. The non-chromate controls and MUV on TCP 

also had salting in the scribe after 2000 hours of ASTM B117 testing while the MUV panels on 

cerium conversion coated (CeCC) substrates had wide spread blister formation and salting in the 

scribe (Figure 54). 

 a) b) 

Figure 53. Optical images of Al 2024-T3 panels after 2000 hours of ASTM B117 salt spray 

testing: a) chromate standard and b) MUV on CrCC. 

60 
 a) b) c) 

Figure 54. Optical images of Al 2024-T3 panels after 2000 hours of ASTM B117 salt spray 

testing: a) non-chromate standard, b) MUV on TCP, and c) MUV on CeCC. 

MUV coatings with CrCC on Alclad 2024 and Alclad 7075 substrates passed filiform corrosion 

testing. MUV coatings with CeCC on Alclad 2024 passed filiform corrosion while MUV with 

CeCC on Alclad 7075 failed filiform testing. The chromate controls passed on Alclad 2024 and 

7075 but the non-chromate controls failed on Alclad 2024 and 7075 substrates. Accelerated 

Xenon-arc weathering after 500 hours indicated that the 60 degree gloss reading was < 2 on the 

MUV coatings on CeCC and CrCC and 3 to 4 on the top coated chromate and non-chromate 

controls (maximum allowed value of 5). The delta E values for the controls was <1, within 

specifications, while the MUV coatings had a delta E of ~5 due to color darkening associated 

with the carbon pigment. 

Initial pencil hardness of the control and MUV panels was 2H. The chromate and non-chromate 

control samples passed Skydrol resistance testing (3H after 30 days) while the MUV coatings on 

CrCC and CeCC failed (less than 6B after 30 days). All 3 of the chromate control and 2 of the 3 

MUV/CrCC samples passed the low temperature flexibility tests (Figure 55). Room temperature 

flexibility test results indicated that the chromate and non-chromate controls had 20% elongation 

before cracking was observed at 10X magnification, 2 of the 3 MUV on CrCC had 10% 

elongation before cracking, and the MUV on CeCC had cracks visible at only a few % elongation 

(Figure 56). Investigations into the source and nature of the blisters that were observed after salt 

spray testing of MUV coatings on CeCC were conducted. Results indicate that blisters did not 

form after exposure to 40°C ambient or 85% relative humidity at 40°C for up to two weeks. 

Blisters only formed during submersion of the panels into DI water, but the blisters decreased in 

size, or were not observable, after the panels were left out in air for a day. Panels with fewer 

blisters performed better in salt spray testing than panels with many blisters, and the adhesion 

strength of the MUV was higher on panels with fewer blisters as well. 

61 
Chromate controls 

MUV on CrCC 

Figure 55. Optical images of Al 2024-T0 panels after low temperature flexibility tests. 

 a) b) 

Figure 56. Optical images of Al 2024-T0 panels after room temperature flexibility tests: a) 

chromate controls and b) MUV on CrCC. 

62 
Summary of MUV Evaluations

Table VIII presents an overall summary of the MUV results from the project. The tests that were 

consistently passed by the MUV coatings during the project are highlighted in blue (Note: the Al 

7075 substrates were not used for many of the tests because the specification calls for Al 2024.) 

Adjustments to MUV formulation throughout the project resulted in the ability of the MUV to 

pass many of the other tests, including wet tape adhesion and low temperature flexibility. Room 

temperature flexibility and accelerated weathering values were close to required specifications 

and did pass requirements in certain instances. The main objective of developing and 

demonstrating a UV curable coating that can provide corrosion protection to high strength 

aluminum alloy substrates was achieved. 

Table VIII - Summary of MUV Evaluation Results 

63 
6. Conclusions and Implications for Future Research/Implementation 

The project was successful in achieving many of the goals and objectives in the original 

proposal. Cerium conversion coatings were able to pass 336 hours of ASTM B117 salt spray 

testing on Al 2024-T3 and Al 7075-T6 with proper surface preparation, deposition conditions, 

and post-treatment. It was determined that substrate preparation significantly altered the surface 

chemical and electrochemical properties of high strength aluminum alloys. Activation of panels 

in strong acid or base solutions removed the native oxides and exposed intermetallic compounds 

in the alloys. Acid activation results in faster CeCC deposition rates, reducing the number of 

spray cycles required to completely cover a substrate from 40 for panels that were degreased to 

1 for panels that were degreased and activated. Alternative surface preparation methods such as 

ultrasonic cleaning, use of abrasive media, and hand application of cleaning solutions, were 

shown to be suitable for and compatible with subsequent CeCC deposition processes. The 

addition of 0.8 g gelatin to deposition solutions was found to decrease the effective deposition 

rate of CeCCs by slowing the nucleation process, improving coating quality and corrosion 

resistance. Investigations on the effect of the pH, Ce concentration, and amount of H2O2 in the 

deposition solution found that a pH of 2.5, concentration of 4 wt.% Ce using CeCl3 salt sources, 

and 20 ml of H2O2 resulted in coatings that performed well in salt spray and electrochemical 

testing and optimized phosphate post-treatment. However, the use of chloride and peroxide 

containing deposition solutions was found to produce sub-surface crevices in the Al substrates. 

Phosphate solution post-treatment of CeCCs could significantly improve the corrosion protection 

of the films. Several phosphate sources and processing conditions were evaluated and it was 

determined that using NH4H2PO4 at pH 4.5 and 85°C for 5 minutes was able to consistently pass 

ASTM B117 criteria. Correlation of salt spray results and electrochemical polarization and 

impedance spectroscopy was excellent after modification of a prohesion-based electrolyte. The 

majority of CeCC depositions were done using a spray method but brush application, immersion, 

and electrolytic processes were also demonstrated to be effective. In almost all cases, it was 

found that a ~400nm thick CeCC was the most effective corrosion coating. All of the knowledge 

gained during the project was used to develop and publish a deposition mechanism for CeCCs 

that has gained recognition and acceptance within the scientific community. 

Development and demonstration that UV curable coatings with inorganic corrosion inhibitors 

could be fully cured in just a few seconds, have good flexibility, adhesion, and fluid resistance, 

and pass corrosion testing was a major breakthrough. There was skepticism at the start of the 

project that highly loaded polymer coatings would be able to pass the requirements for existing 

epoxy based coatings; therefore, chromate and non-chromate epoxy coatings were used as 

reference standards throughout the project in order to directly compare results. Evaluation of 

MUV coatings on TCP conversion coated panels was also done during the project. The 

multifunctional UV curable system repeatedly passed 3000 hours of ASTM B117 salt spray 

testing on chromate conversion coated high strength Al alloys with ~30 wt. % Hybricor 204 

corrosion inhibitor from Wayne Pigments in the MUV. An acrylate-based polymer system was 

used throughout the project along with a two bulb curing system from Fusion, Inc. Initially, 

corrosion inhibitors from Deft and Wayne Pigments were evaluated but it was evident from the 

early stages of the project that Hybricor 204 was the best inhibitor. Application of the MUV was 

done using a drawdown method during the first two rounds of testing in order to conserve 

material. A complete non-chrome coating system of Hybricor 204 inhibitor on CeCC did pass 

64 
ASTM B117 in the first round of testing. A ladder study was done after the first two rounds in 

order to determine the optimum amount of Hybricor 204 and, while a range of values between 27 

and 36 wt% were all effective at inhibiting corrosion, a 29 wt% loading was chosen to develop a 

MUV spray formation by considering all of the desired properties. The first spray deposited 

MUV formulation was done during round three and again demonstrated excellent filiform and 

salt spray corrosion performance, with ~10% elongation, good adhesion, and low gloss values on 

chromate conversion coated panels. Panels with MUV on CeCC developed blisters during 

corrosion testing that led to failure. In an attempt to improve the flexibility of the MUV, lower 

molecular weight oligomers were used during round 4 and, although corrosion performance was 

still very good, there was degradation in the non-corrosion related performance of the MUV. The 

final round of testing was done with a formulation that was a modified version of the formulation 

used in round 3. Darkening of the MUV during accelerated weathering tests and poor 

performance on CeCC, as was the case in round 3, were observed in round 5. Positive results 

from round 5 on chromate conversion coated panels included excellent corrosion protection, 

good adhesion, samples that passed low temperature flexibility testing, and ~10% reverse impact 

flexibility at room temperature. Collectively, the results indicated that the MUV coatings were 

capable of passing most of the required aerospace requirements and that adjustments in 

formulation were able to alter properties as needed. 

The results of this project indicate that a two layer coating system consisting of a non-chromate 

CeCC and UV curable polymer with inorganic corrosion inhibitors is capable of meeting 

aerospace coating requirements, as demonstrated in the first round of testing. Additional research 

is needed understand and optimize the CeCC process and MUV formulation such that 

reproducible results are obtained. The major conclusions that point to the need for future 

research are summarized below. 

• When deposited on high strength aluminum alloys with CrCCs, MUV coatings 

demonstrated excellent performance. This combination appears to be ready for 

demonstration on non-critical components on military aircraft, and implementation of the 

technology onto specific areas of weapons platforms would not require extensive 

investment. 

• The CeCC and MUV consistently pass independent, individual tests but when combined 

into a system do not meet specifications. In particular, the elimination of blisters on 

MUV/CeCC panels during salt spray testing would likely result in passing not only 

ASTM B117 testing but also significantly improve adhesion and flexibility. Some 

additional research focused on elimination of peroxide species from CeCCs or integrating 

the MUV with other non-chromate surface treatments is needed to produce a viable 

chromium-free system. 

• Although the MUV coating passes the most critical performance specifications (i.e., 

corrosion performance, adhesion, etc.), a color change was observed in accelerated 

weathering testing. Changing the type of pigment used in the MUV could address the 

changes in color during accelerated weathering. 

• Coating processes were developed to be compatible with field application. However, 

demonstration of the UV curing system would initially need to be done on a small scale 

for proof of concept followed by large scale operations based on existing processes in 

commercial use. 

65 
The results of this project have shown that the MUV can meet the important performance criteria 

for coatings used on military aircraft. The path forward to implement the technology is 

straightforward and appears to be ready for demonstration/validation. 

7. Literature Cited 

1. “Corrosion Cost and Preventive Strategies in the United States”, Report No. FHWA-RD01-156, CC Technologies and NACE International, September 30, 2001. 

2. “OSHA Proposes Revised Rule on Hexavalent Chromium”, OSHA News Release, 

October 1, 2004. 

3. “Electrodeposition of Cerium Based Coatings for Corrosion Protection of Aluminum 

Alloys”, J. O. Stoffer, T.J. O’Keefe, S. P. Sitaram, P. Yu, X. Lin, E. Morris, U.S. Patent 

5,932,083, Aug. 3, 1999. 

4. “Cerium Based Spontaneous Coating Process For Corrosion Protection of Al Alloys”, 

James O. Stoffer, Thomas J. O’Keefe, Matthew O’Keefe, Eric L. Morris, Scott Hayes, 

Alex Williams, Berny Rivera, Xuan Lin, Patent # 7,048,807, May 23, 2006. 

5. B.R.W. Hinton, D.R. Arnott, N.E. Ryan, Materials Forum 9 (3), 162-73 (1986). 

6. B. Rivera, B. Johnson, M. O’Keefe, and W. Fahrenholtz, Surface and Coatings 

Technology, 176(3), 349 (2003). 

7. S. Geng, W. Pinc, P. Yu, P. Jones, M. O’Keefe, W. Fahrenholtz, and T. O’Keefe, J. of 

Surface Finishing, 2(4) 276-282 (2007). 

8. Pu Yu, Scott A. Hayes, Thomas J. O’Keefe, Matthew J. O’Keefe, and James O. Stoffer, 

J. of the Electrochem. Soc., 153(1), C74-79 (2006). 

9. “Radiation Curing in Coatings”, J. V. Koleske, ASTM International, US, pp.3 (2002). 

10. V.Shukla, M.Bajpai, D.K. Singh, M.Singh, R.Shukla, Pigment & Resin Technology

33(5),272 (2004). 

11. “New Perspectives in product development and pollution control through the use of ultra 

violet polymerization”, A. De Raeve, http://www.unitex.be/Downloads/niet-leden/to2cderaeve.pdf. 

12. “UV curing technical principle and mechanism”, Ciba Specialty Chemicals, 

http://www.cibasc.com/pf/docMDMS.asp?targetlibrary=CHBS_CE_MADS&docnumber

=1628.

66 
8. Appendices

8.1 List of Scientific/Technical Publications 

A. Articles in Peer Reviewed Journals

1. S. Geng, P. Yu, M O’Keefe, W. Fahrenholtz, and T. O’Keefe, “Screening Study of 

Spray Solution Parameters for Depositing Cerium Based Conversion Coatings on Al 

Alloy 2024-T3”, J. Applied Electrochemistry, 40, 551, (2010). 

2. D. Heller, W. Fahrenholtz, and M. O’Keefe, “The Effect of Post-treatment Time and 

Temperature on Cerium Based Conversion Coatings on Al 2024-T3”, Corrosion 

Science, 52, 360 (2010). 

3. W.R. Pinc, P. Yu, M. O'Keefe, and W. Fahrenholtz, "Effect of Gelatin Additions on 

the Corrosion Resistance of Cerium Based Conversion Coatings Spray Deposited on 

Al 2024-T3," Surface and Coatings Technology, 203(23) 3533 (2009). 

4. D. Heller, W. Fahrenholtz, and M. O’Keefe, “Effect of Phosphate Source on the 

Post-treatment and Corrosion Performance of Cerium Based Conversion Coatings on 

Al 2024-T3”, J. Elec. Soc. 156(11), C400 (2009). 

5. D.K. Heller, W.G. Fahrenholtz and M.J. O'Keefe, "The Effect of Phosphate Source 

on the Post-Treatment of Cerium-Based Conversion Coatings on Al 2024-T3 and Its 

Correlation to Corrosion Performance," ECS Trans. 16, 47 (2009). 

6. W. Pinc, S. Geng, M. O’Keefe, W. Fahrenholtz, and T. O’Keefe, “Effects of acid 

and alkaline based surface preparations on spray deposited cerium based conversion 

coatings on Al 2024-T3”, Applied Surface Science, 255, 4061 (2009). 

7. S. Geng, W. Pinc, P. Yu, P. Jones, M. O’Keefe, W. Fahrenholtz, and T. O’Keefe, 

“Influence of Cleaning on the Deposition Rate of Cerium Based Conversion 

Coatings on Aluminum Alloy 2024”, J. of Surface Finishing, 2(4) 276-282 (2007). 

8. P. S. Jones, P. Yu, W.R. Pinc. M.J. O'Keefe, W.G. Fahrenholtz, and T.J. O'Keefe, 

"Spray Deposition of Cerium Oxide-Based Conversion Coatings on Al 2024-T3," 

International Journal of Applied Ceramic Technology, 5(1) 63-73 (2008). 

9. Shaoxin You, Philip Jones, Ajay Padwal, Paul Yu, Matthew O’Keefe, William 

Fahrenholtz, and Thomas O’Keefe, “Response of Nano-crystalline Cerium Based 

Conversion Coatings on Al 2024-T3 To Chloride Environments”, Materials Letters, 

61 (17), 3378 (2007). 

B. Technical Reports

1. Philip Jones, May 2007, MS Thesis, Impact of Processing Parameters on Spray 

Deposition of a Cerium-Based Conversion Coating on Al 2024-T3 

2. William Gammill, December 2009, MS Thesis, Evaluation of Alternative Methods 

for Surface Preparation and Deposition of Cerium-based Conversion Coatings on 

Aluminum Alloys 

3. “Multifunctional UV (MUV) Curable Corrosion Coatings for Aerospace 

Applications”, Matthew J. O’Keefe, William G. Fahrenholtz, and Ben S. Curatolo, 

Metal Finishing, pp. 28-31, February 2010. 

67 
4. “Cerium-Based Conversion Coatings as Alternatives to Hex Chrome”, Matthew J. 

O’Keefe, Shujiang Geng, and Simon Joshi, Metal Finishing, pp. 25-28, May 2007. 

C. Conference or Symposium Scientifically Recognized

1. A. Thomas, D. Heller, W. Gammill* W. Fahrenholtz, M. O’Keefe, J. DeAntoni, and 

B. Curatolo, “Performance of Multifunctional UV (MUV) Curable Corrosion 

Coating Systems to Aerospace Military Test Criteria”, DoD Corrosion Conference, 

Washington DC, Aug 2009. 

2. S. Geng, W. Pinc, S. Joshi, W. Fahrenholtz, M. O’Keefe, T. O’Keefe and P. Yu, 

“Influence of Processing Parameters on Cerium Based Conversion Coatings”, TriServices Corrosion Conference, Denver, CO, Dec 2007. 

3. J. DeAntoni, B. Curatolo, M. O’Keefe and W. Fahrenholtz, “Development and 

Evaluation of Multifunctional Ultraviolet (MUV) Light Curable Coatings for High 

Strength Aluminum Alloys”, Tri-Services Corrosion Conference, Denver, CO, Dec 

2007. 

4. Philip Jones, Ajay Padwal, Paul Yu, Matthew J. O’Keefe, William Fahrenholtz, 

Thomas O’Keefe, “Characterization of Alkaline Cleaned and Cerium Oxide Coated 

Al 2024-T3”, Materials Science and Technology Conference, Product 

Manufacturing Symposium, pp 591-597, Cincinnati, OH, Oct 2006. 

D. Conference of Symposium Abstracts

1. W. Pinc, D. Heller, W. Fahrenholtz, and M. O’Keefe, “The Electrochemical and 

Structural Changes of Cerium Based Conversion Coatings During Exposure to a Salt 

Spray Environment”, Electrochemical Society Meeting, Oct 5-8, 2009, Vienna, 

Austria. 

2. D.K. Heller, W.G. Fahrenholtz, and M.J. O'Keefe, "Electrochemical Analysis of 

Phosphate Treated Cerium Based Conversion Coatings on Al 2024-T3," PRIME 

2008: Pacific Rim Meeting on Electrochemical and Solid State Science, October 12-

17, 2008, Honolulu, HI. 

3. Heller, W. Fahrenholtz, and M. O’Keefe, “The Effect of Phosphate Post-treatment 

Process Variables on Cerium Based Conversion Coating of Al 2024-T3”, MS&T 

Conference, Pittsburgh, PA, Oct 2008. 

4. W. Gammill, W. Fahrenholtz, and M. O’Keefe, “Non-Immersion Surface 

Preparation for Cerium-based Conversion Coatings On Aluminum Substrates”, 

MS&T Conference, Pittsburgh, PA, Oct 2008. 

5. S. Joshi, W. Fahrenholtz, and M. O’Keefe, “The Effect of Phosphate Additions on 

the Corrosion Resistance of Cerium Conversion Coatings on Aluminum Alloy 7075 

– T6”, MS&T Conference, Pittsburgh, PA, Oct 2008. 

6. W. Pinc, W. Fahrenholtz, and M. O’Keefe, “Effect of Gelatin Additions on the 

Corrosion Resistance of Cerium Based Conversion Coatings”, MS&T Conference, 

Pittsburgh, PA, Oct 2008. 

7. S. Geng, P. Yu, M. O’Keefe, W. Fahrenholtz, and T. O’Keefe, “Corrosion Behavior 

of Ce-Based Conversion Coatings on Al Alloy 2024-T3”, MS&T Conference, 

Detroit, MI, Sep 2007. 

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69 

8. S. Joshi, W. Pinc, S. Geng, M. O’Keefe, W. Fahrenholtz, and T. O’Keefe, 

“Characterization of Cerium Conversion Coated Al 7075-T6 Prepared with Alkaline 

and Acid Cleaning Solutions”, MS&T Conference, Detroit, MI, Sep 2007. 

9. Materials Science and Technology (MS&T) Conference, “Corrosion Performance of 

Cerium-Based Conversion Coatings on Aluminum Alloys”, Bill Fahrenholtz and 

Matt O’Keefe, Oct 28, 2009. 

10. SERDP 2008 Symposium, “Development and Evaluation of Multifunctional UV 

(MUV) Curable, Non-Chromate Corrosion Coating Systems”, Matt O’Keefe, Bill 

Fahrenholtz, John DeAntoni, and Ben Curatolo, Wash DC, Dec 3, 2008. 

11. University of Cincinnati, Materials Science and Engineering Seminar, “NonChromate Coatings for Corrosion Protection”, Matt O’Keefe and Bill Fahrenholtz, 8 

May 2008. 

12. Surface Finishing and Repair Issues for Sustaining New Military Aircraft Workshop, 

“Multifunctional UV Coatings and Ce-Based Materials”, Matt O’Keefe, Bill 

Fahrenholtz, John DeAntoni, and Ben Curatolo, Tempe, AZ, Feb 28 2008. 

13. DoD Metal Finishing Workshop, “Ce Based Conversion Coatings”, Matt O’Keefe, 

Hill AFB, UT, May 16, 2007. 

14. GM Tech Center Symposium, “Development of Environmentally Friendly Corrosion 

Coating Systems”, Matt O’Keefe, Warren, MI, Apr 16, 2007. 

15. W. Pinc, S. Geng, S. Joshi, M. O’Keefe, W. Fahrenholtz, and T. O’Keefe, “Effects 

of Acidic and Alkaline Based Surface Preparations of Al 2024-T3 on Spray 

Deposited Cerium-Oxide Conversion Coatings”, MS&T Conference, Detroit, MI, 

Sep 2007.