Examination of Alternative Pretreatments to Hexavalent 

Chromium-Based DOD-P-15328D Wash Primer 

for MIL-A-46100D High Hard Steel Armor 

by Brian E. Placzankis, Chris E. Miller, and John V. Kelley 

ARL-TR-3393 January 2005 

Approved for public release; distribution is unlimited. 
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Army Research Laboratory 

Aberdeen Proving Ground, MD 21005-5069 

ARL-TR-3393 January 2005 

Examination of Alternative Pretreatments to Hexavalent 

Chromium-Based DOD-P-15328D Wash Primer for 

MIL-A-46100D High Hard Steel Armor 

Brian E. Placzankis, Chris E. Miller, and John V. Kelley 

Weapons and Materials Research Directorate, ARL 

Approved for public release; distribution is unlimited. 
ii

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4. TITLE AND SUBTITLE 

Examination of Alternative Pretreatments to Hexavalent Chromium Based 

DOD-P-15328D Wash Primer for MIL-A-46100D High Hard Steel Armor 

5c. PROGRAM ELEMENT NUMBER 

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622105 H84 

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6. AUTHOR(S) 

Brian E. Placzankis, Chris E. Miller, and John V. Kelley 

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U.S. Army Research Laboratory 

ATTN: AMSRD-ARL-WM-MC 

Aberdeen Proving Ground, MD 21005-5069 

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13. SUPPLEMENTARY NOTES 

14. ABSTRACT 

Hexavalent Chromium based compounds with their associated health and environmental risks have necessitated reductions and 

even eliminations of their usage in U.S. Army weapon systems. These compounds are primarily associated with pretreatments 

and conversion coatings applied prior to primers and topcoats that make up the Chemical Agent Resistant Coating (CARC) 

coating system. Despite these hazards, for armor steels such as MIL-A-46100D high hard alloy, hexavalent chromium based 

DOD-P-15328D wash primer is still commonly used. This study explores the effectiveness of wash primer alternatives with 

respect to corrosion, adhesion, and susceptibility to Environmentally Assisted Cracking (EAC) issues. The alternatives studied

were: spray based zinc phosphate in accordance with TT-C-490, grit blast only with no other pretreatment, and grit blast with a 

rust inhibiting sealer. 

15. SUBJECT TERMS

zinc phosphate, MIL-A-46100D, high hard armor steel, wash primer, hexavalent, chromium 

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19a. NAME OF RESPONSIBLE PERSON

Brian E. Placzankis 

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iii

Contents 

List of Figures iv

List of Tables v

Acknowledgments vi

1. Introduction 1

2. Experimental Procedure 2

3. Results 15

3.1 Pull-off Adhesion ..........................................................................................................15 

3.2 Accelerated Corrosion...................................................................................................15 

3.3 Resistance to Flash Rusting...........................................................................................19 

3.4 Rising Step Load (KIEAC) ..............................................................................................32 

4. Discussion 32

5. Conclusions 37

6. References 38

Distribution List 41 
iv

List of Figures 

Figure 1. Brigade Combat Team (BCT) Stryker Interim Armored Vehicle (IAV) in 

Standard Infantry Carrier Vehicle (ICV) configuration.............................................................2 

Figure 2. Process steps for abrasive blast with primer coating applied at MILITEX 

and followed for the laboratory procedure.................................................................................3 

Figure 3. Process steps for abrasive blast with CHEMINHIB 420 abrasive blast at 

MILITEX with primer applied at GDLS, London facility and followed for the 

laboratory procedure. .................................................................................................................4 

Figure 4. Process steps for the proposed spray zinc phosphate followed in the 

laboratory procedure. .................................................................................................................4 

Figure 5. Test chamber configuration used for ASTM B 117-90 neutral salt fog..........................5 

Figure 6. Test chamber configuration used for GM 9540P cyclic corrosion..................................5 

Figure 7. Pull-off hydraulic adhesion test (ASTM D 4541). ..........................................................8 

Figure 8. KIEAC test specimen configuration (25). ........................................................................12 

Figure 9. Crack plane orientation identification codes for rolled plate (24).................................13 

Figure 10. Identification of crack initiation load PIEAC.................................................................13 

Figure 11. Rising step load specimen in test fixture.....................................................................14 

Figure 12. Rising step load test configuration. .............................................................................14

Figure 13. ASTM D 4541 pull-off adhesion results abrasive blast with DOD-P-15328D 

(wash primer) Cr+6 based legacy pretreatment. .......................................................................16 

Figure 14. ASTM D 4541 pull-off adhesion results for abrasive blast only.................................16 

Figure 15. ASTM D 4541 pull-off adhesion results for abrasive blast with 

CHEMINHIB 420 water soluble inhibitor coating..................................................................17 

Figure 16. ASTM D 4541 pull-off adhesion results for abrasive blast with spray zinc 

phosphate pretreatment. ...........................................................................................................17 

Figure 17. 53022(II)/53039A at 1500 hr ASTM B 117-90 salt fog..............................................21 

Figure 18. 53022(II)/64159 at 1500 hr ASTM B 117-90 salt fog. ...............................................22 

Figure 19. Legacy coating system (a) vs. current coating systems (b and c) pretreated with 

spray zinc phosphate at 1500 hr ASTM B 117-90 salt fog......................................................23 

Figure 20. 53022(II)/53039A at 80 cycles GM 9540P cyclic corrosion.......................................25 

Figure 21. 53022(II)/64159 at 80 cycles GM 9540P cyclic corrosion. ........................................26 

Figure 22. Legacy coating system (a) vs. current coating systems (b and c) pretreated with 

spray zinc phosphate at 80 cycles GM 9540P cyclic corrosion...............................................27 

Figure 23. Initial appearance of bare pretreated specimens prior to 100% relative humidity 

exposure. ..................................................................................................................................28 
v

Figure 24. Appearance of bare pretreated specimens after 16 hr of ASTM D 1735 

100% relative humidity exposure. ...........................................................................................29 

Figure 25. Initial appearance of bare pretreated specimens prior to 1 week of 27 °C, 

69% relative humidity ambient laboratory exposure...............................................................30 

Figure 26. Appearance of bare pretreated specimens after 1 week of 27 °C, 

69% relative humidity ambient laboratory exposure...............................................................31 

Figure 27. Average KIEAC for pretreated 4340 and 46100 by orientation.....................................33 

Figure 28. Changes in phosphate quality/appearance from adjustments to free 

acid concentration point values via increases of Henkel Primer 40 to the 

BONDERITE 952 spray zinc phosphate solution. ..................................................................36 

List of Tables 

Table 1. GM 9540P cyclic corrosion test details. ...........................................................................6 

Table 2. Evaluation of scribed coated specimens subjected to corrosive environments - 

ASTM D 1654-79A. ..................................................................................................................7 

Table 3. Laboratory conditions for pull-off adhesion ASTM D 4541............................................8 

Table 4. Typical mechanical properties of MIL-A-46100D high hard armor and other high 

strength steels.............................................................................................................................9 

Table 5. Chemical composition of MIL-A-46100D high hard armor (a, b)....................................10 

Table 6. Precracking conditions for KIEAC CV2 specimens..........................................................11 

Table 7. Readings (psi) for ASTM D 4541 pull-off adhesion. .....................................................18 

Table 8. ASTM D 1654-79A scribe creepback ratings for 1500 hr ASTM B 117-90 salt fog 

exposure. ..................................................................................................................................20 

Table 9. ASTM D 1654-79A scribe creepback ratings for 80 cycle GM 9540P cyclic 

corrosion exposure...................................................................................................................24 

Table 10. Experimental conditions and KIEAC values for rising step load specimens. .................34 
vi

Acknowledgments 

The authors thank the following people for their knowledge and support during the performance 

of this study: Carmen Uffen, Keith Clavett, and Lilliana Pereira of GDLS, London, Ontario, for 

information and assistance on current coating processes; Janet Byrne of PPG Industries, Euclid, 

OH, who cross-referenced the Canadian and U.S. product names and supplied PPG product 

samples for evaluation and information for product mixing/application procedures; John Beatty 

and Jonathan Montgomery of the U.S. Army Research Laboratory for their additional knowledge 

in high strength armor steels and assistance in troubleshooting the tensile test load frame; and 

finally, the authors wish to recognize Terry Dean and Geoff Hoerauf of PM BCT for their 

funding, guidance, and, most of all, their patience with respect to the unanticipated additional 

time needed for completion of this study. 
1

1. Introduction 

Hexavalent Chromium based compounds with their associated health and environmental risks 

have necessitated reductions and even eliminations of their usage in U.S. Army weapon systems 

(1). These compounds are primarily associated with pretreatments and conversion coatings 

applied prior to primers and topcoats that make up the Chemical Agent Resistant Coating 

(CARC) coating system. Despite these hazards, for armor steels such as MIL-A-46100D (2) 

high hard alloy, hexavalent chromium based DOD-P-15328D (3) wash primer is still commonly 

used. This study explores the effectiveness of wash primer alternatives with respect to corrosion, 

adhesion, and susceptibility to environmentally assisted cracking (EAC) issues. The alternatives 

studied were: spray based zinc phosphate in accordance with TT-C-490D (4), grit blast only 

with no other pretreatment, and grit blast with a rust inhibiting sealer. 

Historically, DOD-P-15328D wash primer has extensively been used as one possible 

pretreatment portion of the CARC coating system for steel and aluminum substrates. The 

hexavalent chromium component present in the wash primer promotes adhesion of the primer to 

the substrate and inhibits the nucleation and growth of corrosion sites. In order to comply with 

current Army policies and DOD directives, all new Army acquisition must be hexavalent 

chromium free. Three hexavalent chromate free solutions were selected for study based upon 

feedback from the Brigade Combat Team (BCT) Stryker Interim Armored Vehicle (IAV) 

Environmental Management Team and process engineers at the General Dynamics Land 

Systems (GDLS) London, Ontario, Canada assembly facility for the Stryker family of armored 

vehicles (figure 1). These three pretreatments were: Abrasive blast only, Abrasive Blast + PPG 

CHEMINHIB*

 420 (5), and Abrasive Blast + Henkel Surface Technologies BONDERITE† 952 

spray based zinc phosphate. Performance criteria applied to replacement candidates for 

hexavalent chromate based DOD-P-15328D wash primer included corrosion resistance and 

adhesion, as well as process controls and ease of application during manufacturing. 

A particular concern for this study is the armor steel itself. The yield strength for 

MIL-A-46100D high hard armor steel used in Stryker and other weapon systems is at or beyond 

the 1400 MPa (6) level commonly noted for high risk to cracking via hydrogen exposure near the 

surface. This form of hydrogen attack, usually referred to as EAC, can occur as a result of 

corrosion in a natural environment and can also be introduced via aqueous surface processing 

procedures such as cleaning or plating. Zinc phosphate as a pretreatment for steels is common in 

the automotive industry; however, it is normally used on much lower strength steels. The 

phosphating process is aqueous by nature and includes acidic steps. Due to the high strength 

level of the MIL-A-46100D armor steel, the potential for environmentally assisted cracking from 

potential hydrogen sources such as a spray zinc phosphate remains a critical concern and cannot 

be underestimated. 

 

*

CHEMINHIB is a registered trademark of PPG Industries, Inc., Euclid, OH. 

†

BONDERITE is a registered trademark of Henkel Surface Technologies, Madison Heights, MI. 
2

Figure 1. Brigade Combat Team (BCT) Stryker Interim 

Armored Vehicle (IAV) in Standard Infantry 

Carrier Vehicle (ICV) configuration. 

Funding for this study was provided by the U.S. Army Tank Automotive and Armaments 

Command (TACOM) via PM BCT. 

2. Experimental Procedure 

High hard armor steel test panels (120 each nominally 10.16 × 15.24 × 0.635 cm) of MIL-A46100D were prepared. Prior to pretreatment and testing, all panels were clearly designated for 

their respective pretreatments. Due to the extreme hardness of the material, panel identification 

was executed via removal of panel corners through surface grinding. The three panel processing 

sets and their quantities prepared were identified as follows: 

• All four corners intact–Abrasive Blast (30) 

• One corner removed–Abrasive Blast with CHEMINHIB 420 (30) 

• Two corners removed–Abrasive Blast with spray zinc phosphate (30) 

Each of the three sets of test panels were further subdivided and coated with two different 

primer/topcoat systems: 

• MIL-P-53022-10 (7) (type II) primer with MIL-C-53039A (8) topcoat (15) 

• MIL-P-53022-10 (type II) primer with MIL-DTL-64159 (9) (type II) topcoat (15) 

An additional control set of 30 panels representative of legacy processing methods was prepared 

with hexavalent chromium containing DOD-P-15328D and was coated with MIL-P-53022-10 

(type I) primer and MIL-C-46168 (10) topcoat. All of the test panels’ respective primer coats 
3

were applied within 24 hr after the surface preparation and pretreatment. The abrasive blasting 

step was performed on all panels and consisted of SiC media applied to a SSPC-SP 10 (11) 

near white metal finish with a 1.5-mil profile. Applications of spray zinc phospate and 

CHEMINHIB 420 surface pretreatments were performed on the blasted panels following 

manufacturer’s instructions and procedures used at the GDLS London facility. To avoid 

confusion, it should be noted that KLEENINHIB*

 486 (12) product used in cleaning and 

shipping phases for bare Stryker hulls is also known by the trade name CHEMKLEEN 340 in the 

United States. Both of these products are chemically identical. The CHEMINHIB 420 was 

prepared from PPG Industries RECOOL* ADDITIVE 15 (13) concentrate. Additional spray zinc 

phosphated panels were set aside and sampled for coating weight using a heated chromic acid 

stripping solution. The spray zinc phosphate applied on the 46100 corrosion test panels fell 

within the range for zinc phosphate coating weight specified in TT-C-490 and averaged 320 

mg/ft2. The application procedures for the different pretreatment scenarios as performed in 

production and in laboratory conditions are described in figures 2–4 (14–17). 

Figure 2. Process steps for abrasive blast with primer coating applied at MILITEX and followed for the 

laboratory procedure. 

Two corrosion test chambers, a Harshaw Model 22 standard neutral salt fog and an Attotech 

Model CCT-NC-30 cyclic corrosion test chamber, were used to evaluate the armor steel test 

panels. Figures 5 and 6 show the test chambers used throughout the study. Immediately prior 

to exposure, the panels were all “X” scribed using a standard carbide tipped hardened steel 

scribe. The scribed panels were placed into the respective chambers and exposed to ASTM B 

117-90 (18) and General Motors 9540P (19) accelerated corrosion test environments. The 

ASTM B 117-90 neutral salt fog conditions are 95°F with saturated humidity and atomized fog 

of 5% NaCl solution. The GM 9540P test consists of 18 separate stages that include the 

following: saltwater spray, humidity, drying, ambient, and heated drying. The environmental 

conditions and duration of each stage for one complete 9540P cycle are provided in table 1. The 

standard 0.9% NaCl, 0.1% CaCl2, 0.25% NaHCO3 test solution was used. In addition, the cyclic 

chamber was calibrated with standard steel mass loss calibration coupons as described in the 

GM 9540P test specification. 

 

*

KLEENINHIB and RECOOL are registered trademarks of PPG Industries, Inc., Euclid, OH. 
4

Figure 3. Process steps for abrasive blast with CHEMINHIB 420 abrasive blast at MILITEX with primer 

applied at GDLS, London facility and followed for the laboratory procedure. 

Figure 4. Process steps for the proposed spray zinc phosphate followed in the laboratory procedure.

 

Note: Fixodene and Parcolene are registered trademarks of Henkel Surface Technologies, Madison Heights, MI. 
5

Figure 5. Test chamber configuration used for ASTM B 

117-90 neutral salt fog. 

Figure 6. Test chamber configuration used for GM 9540P cyclic corrosion. 
6

Table 1. GM 9540P cyclic corrosion test details. 

Interval Description Time 

(min) 

Temperature 

(±3 °C) 

1 Ramp to salt mist 15 25 

2 Salt mist cycle 1 25 

3 Dry cycle 15 30 

4 Ramp to salt mist 70 25 

5 Salt mist cycle 1 25 

6 Dry cycle 15 30 

7 Ramp to salt mist 70 25 

8 Salt mist cycle 1 25 

9 Dry cycle 15 30 

10 Ramp to salt mist 70 25 

11 Salt mist cycle 1 25 

12 Dry cycle 15 30 

13 Ramp to humidity 15 49 

14 Humidity cycle 480 49 

15 Ramp to dry 15 60 

16 Dry cycle 480 60 

17 Ramp to ambient 15 25 

18 Ambient cycle 480 25 

In order to quantify the corrosion, ASTM B 117-90 salt fog panels were numerically rated for 

scribe corrosion creepback damage at weekly intervals up to 1512 hr using method ASTM D 

1654-79A (20). The GM 9540P panels were also rated using ASTM D 1654-79A for scribe 

creepback corrosion at 10, 20, 40, 60, 70, and 80 cycles. In addition to the numeric ratings, 

representative panels chosen from the first exposure interval were digitally scanned at each 

rating interval and saved as high quality graphics files at 600 dpi to visually chronicle the 

corrosion damage. To facilitate easier viewing of the inevitable large quantities of raw data from 

this test matrix, color codes were assigned based upon ranges of ASTM D 1654-79A ratings. 

Table 2 depicts the ASTM D 1654-79A rating parameters and also defines the colors and their 

respective rating ranges. In addition to the color coding, for panels where coating blistering from 

corrosion occurred in areas away from the scribe, the numerical ratings appear boldfaced and 

underscored. 

For evaluating coating adhesion to the different surface treatments, pull-off adhesion was chosen 

as the basis for adhesion evaluation over scribe and tape based methods such as ASTM D 3359 

(21). Tape-based measurements were attempted, however, the coarse, irregular surface 

topography and extreme substrate hardness inherent to 46100 armor steel led to rapid dulling and 

even breaking of scribing tools as well as inconsistent and unusable results. The pull-off 

adhesion measurements assessing the effects of pretreatment or surface preparation at the 

substrate were performed in accordance with ASTM D 4541 (22). An Elcometer Model 108 

hydraulic adhesion test equipment (HATE) was used for this procedure. In addition to being a 

more quantitative test method, pull-off adhesion is also less prone to human elements in testing, 

such as variations in pressure applied during scribing as well as interpretation and perception of 

results. For the pull-off adhesion test, a loading fixture commonly referred to as a “dolly” is 
7

Table 2. Evaluation of scribed coated specimens subjected to 

corrosive environments - ASTM D 1654-79A. 

Rating of Failure at Scribe (Procedure A) 

Representative Mean Creepage From Scribe 

(mm) (in) 

Rating Number 

Over 0 0 10 

Over 0 to 0.5 0 to 1/64 9 

Over 0.5 to 1.0 1/64 to 1/32 8 

Over 1.0 to 2.0 1/32 to 1/16 7 

Over 2.0 to 3.0 1/16 to 1/8 6 

Over 3.0 to 5.0 1/8 to 3/16 5 

Over 5.0 to 7.0 3/16 to 1/4 4 

Over 7.0 to 10.0 1/4 to 3/8 3 

Over 10.0 to 13.0 3/8 to 1/2 2 

Over 13.0 to 16.0 1/2 to 5/8 1 

Over 16.0 to more 5/8 to more 0 

secured normal to the coating surface using an adhesive. The adhesive used was cyanoacrylate. 

After allowing the adhesive to cure for 24 hr at 40 °C in dry conditions (table 3), the attached 

dolly was inserted into the test apparatus. The load applied by the apparatus was gradually 

increased and monitored on the gauge until a plug of coating was detached. The failure value (in 

psi) was recorded and the failure mode was characterized. The pull-off test apparatus and dolly 

configuration are illustrated in figure 7. For pull-off data to be valid, the specimen substrate 

must be of sufficient thickness to ensure that the coaxial load applied during the removal stage 

does not distort the substrate material and cause a bulging or “trampoline effect.” When a thin 

specimen is used, the resultant bulge causes the coating to radially peel away outwards from the 

center instead of being uniformly pulled away in pure tension and thus results in significantly 

lower readings than for identically prepared specimens at greater substrate thickness. At 0.25 in, 

all of the armor panels evaluated in the test matrix had adequate thickness for valid pull-off test 

results. Measurements were obtained by utilizing the five remaining specimens from each 

pretreatment coated with MIL-P-53022-10 (type II) primer with MIL-DTL-64159 (type II) 

topcoat except for the controls which used DOD-P-15328D and were coated with MIL-P53022-10 (type I) primer and MIL-C-46168 topcoat. Pull-off adhesion measurements attempted 

with the MIL-C-53039A topcoated specimens all resulted in coating interlayer adhesive failures 

at the primer/ topcoat interface and thus could not be used to assess the relative effect on coating 

adhesion imparted by the pretreatment or surface preparation at the substrate. Any other failure 

measurements due to coating separation between the primer and topcoat layers or at the topcoat 

surface with the cyanoacrylate adhesive were also rejected. 

In order to assess the relative resistance of pretreatment alternatives to flash rusting in a 

production environment, humidity testing was conducted on test panels prepared with only the 

surface preparation or pretreatment alternatives. Surplus panels from the adhesion study were 

abrasive blasted and prepared in four different configurations with five replicate panels for: 
8

• Abrasive blast only. 

• Abrasive blast with KLEENINHIB 486, sealed with CHEMINHIB 420. 

• Abrasive blast and spray zinc phosphate (BONDERITE 952 w/Henkel clean stages). 

• Abrasive blast with KLEENINHIB 486 and spray zinc phosphate (BONDERITE 952). 

Table 3. Laboratory conditions for pull-off adhesion ASTM D 4541. 

Adhesive Type Cyanoacrylate 

Cure time (hr) 24 

Temperature (°C) 40 

Percent relative humidity ~0 

Substrate material MIL-A-46100D 

Substrate thickness (in) 0.25 

Substrate surface profile Abrasive blast (1.5 mil) 

Pretreatment types 

DOD-P-15328D 

None 

CHEMINHIB 420 

Spray zinc phosphate 

Coating types CARC 53033(I)/46168 

CARC 53022(II)/64159 

Coating thickness (mils) ~5.5 (including profile) 

Figure 7. Pull-off hydraulic adhesion test (ASTM D 4541). 
9

The humidity exposure was conducted in accordance with ASTM D 1735 (23) at saturated levels 

for 16 hr. Additional panels were also set aside in ambient laboratory conditions with relative 

humidity ranging from 60% to 70% for 1 week. For both exposures, the panels were digitally 

scanned prior to as well as after exposure. 

Finally, resistance to environmentally assisted cracking was assessed using the rising step load 

method for determination of KIEAC. For this procedure, CV2 Charpy specimens of MIL-A46100D and VAR 4340 were machined in longitudinal-transverse (L-T) and transverselongitudinal (T-L) orientations in accordance with ASTM E 399-97 (24, 25). Table 4 contains 

mechanical properties typical for these alloys and table 5 displays the composition specifications 

for MIL-A-46100D. The pretreatments evaluated for these specimens included: DOD-P15328D wash primer, and spray zinc phosphate for the MIL-A-46100D steel and only spray zinc 

phosphate for the 4340 steel. Unlike the 46100 test panels, the charpy specimens were not 

abrasive blasted prior to pretreatment. The 4340 steel specimens were included for cross 

referencing of MIL-A-46100D to known materials. Specimen fatigue precracking was carried 

out using three stages, each consisting of decreasing loading levels. In the first precracking 

stage, the load was maintained to keep stress intensity values below 80% of the estimated 

experimental critical stress intensity and the stress ratio (σmax/σmin) was kept between –1 and 

+0.1. In the intermediate stage, the cycling load was reduced to maintain the stress intensity 

value as crack growth occurred and the intact cross section was reduced. For the final stage of 

precracking, the load was further reduced so the final value of Kmax was unlikely to exceed 60% 

of the estimated value for KI during experimentation. Additionally, the final value for Kmax/E did 

not exceed 0.0032 m1/2, where E is Young’s modulus. Precrack length, represented by the 

dimensionless expression a/W (crack length over specimen width), was maintained near 0.5. 

The fatigue precrack loading sequences for the KIEAC specimens are listed in table 6. 

Table 4. Typical mechanical properties of MIL-A-46100D high hard armor and other high strength 

steels. 

Mechanical Property 46100 HRc 48–51 VAR 4340 HRc 52–54 AISI 1095 HRc 48015050 

UTS (MPa) 1825 1916 1696 

0.2% YS (MPa) 1440 1572 1393 

Elongation (%) 10 12.5 7.0 

RA (%) 40 37.9 19.6 

Specimens were then fastened into a double cantilever array test fixture under aqueous 

conditions with 3.5% NaCl solution at open circuit potential conditions. Specimens were loaded 

by incremental steps in accordance with ASTM F 1624-95 (26) using an Instron model 4301 

hydraulic load frame apparatus. The specimen load values versus time were recorded via 

Labview interface to a computer data file. The calculation for the onset of environmentally 

assisted cracking, or KIEAC, was derived as follows for cantilever bending from the four-point 

bending expression. 

f ( ) a / W

BW

M a

K IEAC

IEAC ×

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

= 2

6 π , (1) 
10

Table 5. Chemical composition of MIL-A-46100D high hard armor (a, b). 

Element 

 Maximum 

Range Percent 

Maximum 

Limit Percent 

Carbon 0.1 0.32 

Manganese Up to 1.00 in include 0.3 — 

Over 1.00 0.4 — 

Phosphorus — 0.020c

Sulfur — 0.010c

Silicon Up to 0.60 in include 0.2 — 

Over 0.60 in to 1.00 in include 0.3 — 

Nickel 0.5 — 

Chromium Up to 1.25 in include 0.3 — 

Over 1.25 in 0.4 — 

Molybdenum Up to 0.20 in include 0.07 — 

Over 0.20 in 0.15 — 

Vanadium 0.15 — 

Boron — —d

Copper — 0.25e

Titanium — 0.10e

Zirconium — 0.10e

Aluminum — 0.10e

Lead — 0.01e

Tin — 0.02e

Antimony — 0.02e

Arsenic — 0.02e 

a

 This table lists the maximum range for elements of the manufacturer’s established chemical composition. 

b

 Elements not listed in this table, but intentionally added, shall be reported. 

c

 Phosphorus and sulfur should be controlled to the lowest attainable levels but, in no case, should the 

combined phosphorus and sulfur content exceed 0.025%. 

d

 When the amount of boron is specified in the alloy, its content so determined by heat analysis shall not 

exceed 0.003%. 

e

 When the amount of an element is less than 0.02% the analysis may be reported as 0.02%. 

where 

2 3 4 f ( a / W ) = 1.122 –1.40 ( a / W )+ 7.33 ( a / W ) –13.08 ( a / W ) +14.00( a / W) , (2) 

where 

MIEAC = the applied moment necessary to induced cracking, 

B = the specimen thickness, 

W = the specimen depth, and 

a = the initial crack length. 

For double cantilever bending conditions, the term MIEAC becomes PIEAC, where PIEAC is the load 

necessary to induce critical cracking and S is the length of the moment arm. This yields the 

utilized expression: 
11

Table 6. Precracking conditions for KIEAC CV2 specimens. 

Sample ID Precrack Load 

(lb) 

Number of Cycles 

Precrack Length 

Side 1/Side 2 

(in) 

Average Crack 

Length “a” 

(in) 

715037 1200 

800 

600 

14000 

9000 

37000 

0.098/0.113 

0.119/0.125 

0.183/0.181 

0.1820 

715038 1200 

800 

600 

13000 

9000 

43000 

0.105/0.101 

0.121/0.117 

0.181/0.181 

0.1810 

715042 1200 

800 

600 

26000 

10000 

37000 

0.118/0.100 

0.134/0.125 

0.182/0.181 

0.1815 

715043 1200 

800 

600 

29000 

10000 

38000 

0.134/0.104 

0.148/0.125 

0.193/0.180 

0.1865 

715047 1200 

800 

600 

14000 

12000 

49000 

0.103/0.108 

0.121/0.127 

0.184/0.189 

0.1865 

715048 1200 

800 

600 

14000 

11000 

47000 

0.093/0.115 

0.115/0.132 

0.180/0.188 

0.1840 

715051 1200 

800 

600 

20000 

16000 

53000 

0.109/0.102 

0.125/0.129 

0.181/0.185 

0.1865 

715052 1200 

800 

600 

20000 

18000 

44000 

0.105/0.105 

0.127/0.127 

0.181/0.183 

0.1830 

715053 1200 

800 

600 

22000 

14000 

56000 

0.118/0.088 

0.137/0.111 

0.200/0.176 

0.1820 

715054 1200 

800 

600 

21000 

15000 

70953 

0.098/0.113 

0.098/0.113 

0.098/0.113 

0.1880 

715057 1200 

800 

600 

21000 

12000 

16000 

0.115/0.111 

0.141/0.141 

0.186/0.191 

0.1885 

715064 1200 

800 

600 

16000 

10000 

29000 

0.107/0.103 

0.122/0.124 

0.187/0.188 

0.1875 

f ( ) a / W

BW

P S a

K IEAC

IEAC ×

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

= 2

6 π , (3) 

where f(a/W) varies between 2.3 and 3.2 for a/W values between 0.45 and 0.55, respectively 

(27, 28). 

The initial crack length was determined by averaging the measured values visible on each side of 

the charpy specimen that ran perpendicular to the crack front. The K1EAC values calculated were 

compared among the pretreatments and against historic values measured for untreated high hard 

steel to determine whether any pretreatment degraded the material and exacerbated 
12

environmentally assisted cracking (29, 30). The dimensions for the CV2 specimens, their 

orientations with respect to the major axis’ of the rolled armor plate, and the configuration of the 

rising step load equipment are shown in figures 8–12. 

Figure 8. KIEAC test specimen configuration (25). 
13

Figure 9. Crack plane orientation identification codes for rolled plate (24). 

Figure 10. Identification of crack initiation load PIEAC. 
14

Figure 11. Rising step load specimen in test fixture. 

Figure 12. Rising step load test configuration.
15

3. Results 

3.1 Pull-off Adhesion 

With the exception of specimens pretreated with DOD-P-15328D wash primer, all of the surface 

pretreatments showed consistent repeatable readings for adhesion data collected and plotted in 

figures 13–16 and listed in table 7. As mentioned in the procedure, the readings for abrasive 

blast, abrasive blast with CHEMINHIB 420, and spray zinc phosphate, were all collected from 

panels coated with MIL-P-53022-10 (type II) primer and MIL-DTL-64159 waterborne topcoat. 

Pull-off readings were attempted on the MIL-C-53039A coated specimens however the pull-off 

separations all occurred consistently in the 2200–2500 psi range as adhesive separations between

the MIL-P-53022-10 (type II) primer and the MIL-C-53039A topcoat and were thus not 

applicable for evaluation of pretreatment effects on adhesion. Abrasive blast and abrasive blast 

prepared with CHEMINHIB 420 water soluble flash rust inhibiting coating, the two procedures 

currently used at GDLS for Stryker production in particular had very tightly grouped data and 

both averaged within 100 psi of each other at 3411 psi and 3494 psi respectively. For spray zinc 

phosphate pretreated panels the average pull-off adhesion reading was 3304 psi, down roughly 

150 psi from the average readings from panels prepared with abrasive blast and abrasive blast 

with CHEMINHIB 420. All of the current and proposed pretreatments had significantly better 

adhesion performance than the legacy system consisting of DOD 1538 wash primer with MIL-P53022-10 (type I) primer with MIL-C-46168D two component solvent-borne topcoat. The 

increases ranged from 16% for spray zinc phosphate to 21% for abrasive blast with 

CHEMINHIB 420 over the wash primer baseline average pull-off adhesion value of 2775 psi. 

3.2 Accelerated Corrosion 

For all of the panels exposed in ASTM-B-117-90 neutral salt fog and GM 9540P, the dominant 

failure mode was creepback from the scribe via blistering as rated under ASTM-D-1654-79A. In 

addition to the creepback rating, severity color coding described in table 2, additional corrosion 

characterization such as blistering away from the scribe was illustrated through application of 

diagonal cross-hatching texture to the color coded cells. 

For neutral salt fog testing, many of the panels, especially the abrasive blast and the abrasive 

blast with CHEMINHIB 420 panels, had secondary blistering away from the scribed areas. For 

these panels, onset exposures for the nonscribe blistering occurred at 500 and 1176 hr, 

respectively, for the waterborne and solvent-borne topcoated specimens. Interestingly, despite 

poorer performance for nonscribe areas, scribe creepback ratings for waterborne topcoated 

abrasive blast, and abrasive blast with CHEMINHIB 420 were slightly improved vs. their 

solventborne counterparts. The spray zinc phosphate and wash primer treated panels had much 
16

Figure 13. ASTM D 4541 pull-off adhesion results abrasive blast with DOD-P-15328D (wash 

primer) Cr+6 based legacy pretreatment. 

Figure 14. ASTM D 4541 pull-off adhesion results for abrasive blast only. 
17

Figure 15. ASTM D 4541 pull-off adhesion results for abrasive blast with CHEMINHIB 

420 water soluble inhibitor coating. 

Figure 16. ASTM D 4541 pull-off adhesion results for abrasive blast with spray zinc phosphate 

pretreatment. 
18

Table 7. Readings (psi) for ASTM D 4541 pull-off adhesion. 

Abrasive Blast (None) 

53022(II)/64159 

CHEMINHIB 420 

53022(II)/64159 

Spray Zinc Phosphate 

53022(II)/64159 

DOD-P-15328D (Wash Primer) 

53022(I)/46168 

3260 3500 3250 2400 

3380 3500 3400 2400 

3460 3460 3450 2150 

3610 3410 3400 2770 

3520 3570 3260 2980 

3410 3510 3300 2720 

3300 3600 3200 3040 

3200 3520 3310 3000 

3470 3410 3460 2300 

3460 3520 3610 3200 

3440 3600 3090 2860 

3410 3680 3400 2800 

3400 3620 3540 2970 

3370 3510 3390 2990 

3360 3660 3240 2810 

3550 3580 3380 3100 

3570 3450 3410 2720 

3420 3490 3400 2780 

3400 3480 3000 2890 

3290 3610 3240 2720 

3170 3520 3420 2340 

3460 3620 3160 2250 

3480 3490 3260 3110 

3610 3400 3240 2310 

3240 3410 3310 2300 

3050 3400 3410 3060 

3490 3220 3320 2960 

3520 3190 3200 2800 

3410 3300 3260 2690 

3370 3490 3050 3030 

3690 3390 3300 3260 

— 3710 3560 2860 

— — 3140 3100 

— — 3230 2690 

— — 3270 — 

— — 3630 — 

— — 3200 — 

— — 3300 — 

— — 3510 — 

— — 3480 — 

— — 3280 — 

— — 3420 — 

— — 3190 — 

— — 3100 — 

— — 3290 — 

— — 3340 — 

— — 3190 — 

— — 3260 — 

— — 2870 — 

— — 3320 — 

Note: All pull-off separation modes were adhesive at the substrate. 
19

better performance, only two of the waterborne topcoated zinc phosphate had any blistering 

away from the scribe, the solvent-borne topcoated zinc phosphated panels and all of the wash 

primer treated panels remained blister free in the nonscribe areas through 1500 hr. For blistering 

at the scribe, the wash primer panels fared no better than abrasive blast or abrasive blast with 

CHEMINHIB 420. When evaluating the neutral salt fog panels for overall performance, in 

scribed and nonscribed areas, the vast majority of spray zinc phosphated panels performed better 

than or equal to the other pretreatments across all replicates. Table 8 displays the ratings at 

various exposures and characterizes the corrosion using the color coding and patterns described 

above. Digital photographs comparing the pretreatments with waterborne and solventborne 

topcoats and also the legacy system with DOD-P-15328D and MIL-C-46168 at 1500 hr are 

displayed in figures 17–19. 

The performance gains noted in neutral salt fog exposure for spray zinc phosphate were even 

more pronounced in GM 9540P cyclic exposure. Spray zinc phosphate scribe creepback ratings 

showed roughly a 2:1 improvement in performance ratio throughout the eighty cycle duration vs. 

abrasive blast and abrasive blast with CHEMINHIB 420. None of the panels tested in GM 

9540P exhibited blistering away from the scribe. In contrast to salt fog, no significant 

differences were observed between waterborne and solvent-borne topcoated panels. Cyclic 

corrosion performance at 80 cycles for DOD-P-15328D wash primer was inconsistent with some 

of the replicate panels performing very well while others rated low or failed completely due to 

excessive blister growth from the scribed region. The improvement in scribe creepback 

corrosion performance gained using the spray zinc phosphating is visible in table 9 and is 

apparent across all of the exposure intervals. As in neutral salt fog, digital photographs 

comparing the pretreatments with waterborne and solvent-borne topcoats and also the legacy 

system with DOD-P-15328D and MIL-C-46168 at 80 cycles are displayed in figures 20–22. 

3.3 Resistance to Flash Rusting 

In order to assess pretreatments from a production perspective, the three main test pretreatments 

(abrasive blast, abrasive blast with CHEMINHIB 420, and spray zinc phosphate) were applied to 

the 46100 steel and exposed without primer and topcoat to ambient laboratory conditions at 

27 °C with relative humidity ranging from 60 to 70% and to ASTM-D-1735 at 35 °C with 100% 

relative humidity. One additional hybrid set of panels was prepared using the KLEENINHIB 

486 process which is the surface cleaning step used for CHEMINHIB 420 but was then spray 

zinc phosphated using the BONDERITE 952 with the PARCOLENE 99 rinse thus effectively 

substituting the existing production cleaning step for the Henkel surface prep stages. Before and 

after exposure scans of the treatments are pictured in figures 23–26. The initial surfaces showed 

almost no difference in appearance between the abrasive blast and abrasive blast with 

CHEMINHIB 420 prepared panels. The spray zinc phosphate and spray zinc phosphate cleaned 

with KLEENINHIB 486 both showed effective deposition of the zinc phosphate crystals 

however, there was also noticeable flash rusting present on the KLEENINHIB 486 cleaned spray 

zinc phosphate panels. Panels exposed in 16 hr at 100% RH show rusting on all of the pretreated
20

Table 8. ASTM D 1654-79A scribe creepback ratings for 1500 hr ASTM B 117-90 salt fog exposure. Note: Boldfaced and underscored ratings denote coating blistering in areas away from the scribe. 

Panel # Pretreatment Primer/Topcoat 144 Hours 336 Hours 500 Hours 672 Hours 840 Hours 1008 Hours 1176 Hours 

GB1s Gritblast 53022(II)/53039 99754 4 3 

GB2s Gritblast 53022(II)/53039 98754 3 3 GB3s Gritblast 53022(II)/53039 9 9 6 55 4 4 GB4s Gritblast 53022(II)/53039 99554 4 3 GB5s Gritblast 53022(II)/53039 98655 4 4 

GB1w Gritblast 53022(II)/64159 9766 5 4 4 GB2w Gritblast 53022(II)/64159 9 8 7 6 4 4 4 GB3w Gritblast 53022(II)/64159 99666 5 5 GB4w Gritblast 53022(II)/64159 9 7 7 5 5 5 5 GB5w Gritblast 53022(II)/64159 9 8 6 5 4 3 3 

P1s Spray Zn Phosphate 53022(II)/53039 98665 5 5 P2s Spray Zn Phosphate 53022(II)/53039 98765 5 5 P3s Spray Zn Phosphate 53022(II)/53039 98766 5 5 P4s Spray Zn Phosphate 53022(II)/53039 99655 4 4 P5s Spray Zn Phosphate 53022(II)/53039 98765 5 4 

P1w Spray Zn Phosphate 53022(II)/64159 9776 6 5 4 

P2w Spray Zn Phosphate 53022(II)/64159 98655 5 5 P3w Spray Zn Phosphate 53022(II)/64159 96666 5 5 P4w Spray Zn Phosphate 53022(II)/64159 98665 5 5 P5w Spray Zn Phosphate 53022(II)/64159 9866 5 4 4 

C1s Cheminhib 420 53022(II)/53039 98654 3 3 C2s Cheminhib 420 53022(II)/53039 99555 4 4 C3s Cheminhib 420 53022(II)/53039 99754 2 2 C4s Cheminhib 420 53022(II)/53039 97754 4 3 C5s Cheminhib 420 53022(II)/53039 99744 3 3 

C1w Cheminhib 420 53022(II)/64159 9 8 7 5 5 4 4 C2w Cheminhib 420 53022(II)/64159 99755 4 4 C3w Cheminhib 420 53022(II)/64159 9 8 7 6 5 5 4 C4w Cheminhib 420 53022(II)/64159 9 9 6 5 5 4 4 C5w Cheminhib 420 53022(II)/64159 9 8 7 5 5 5 4 

WP1 DoD-P-15328 53022(I)/46168 No Data No Data No Data No Data No Data No Data No Data 

WP2 DoD-P-15328 53022(I)/46168 No Data 7433 3 3 

WP3 DoD-P-15328 53022(I)/46168 No Data No Data No Data No Data No Data No Data No Data 

WP4 DoD-P-15328 53022(I)/46168 No Data No Data No Data No Data No Data No Data No Data WP5 DoD-P-15328 53022(I)/46168 No Data No Data No Data No Data No Data No Data No Data 
21

Figure 17. 53022(II)/53039A at 1500 hr ASTM B 117-90 salt fog. 
22

Figure 18. 53022(II)/64159 at 1500 hr ASTM B 117-90 salt fog. 
23

Figure 19. Legacy coating system (a) vs. current coating systems (b and c) pretreated with spray 

zinc phosphate at 1500 hr ASTM B 117-90 salt fog. 
24

Table 9. ASTM D 1654-79A scribe creepback ratings for 80 cycle GM 9540P cyclic corrosion exposure. 

Panel # Pretreatment Primer/Topcoat 10 Cycles 20 Cycles 40 Cycles 60 Cycles 70 Cycles 80 C

GB1s Gritblast 53022(II)/53039 7 4 2 00

GB2s Gritblast 53022(II)/53039 74322GB3s Gritblast 53022(II)/53039 73211 

GB4s Gritblast 53022(II)/53039 6 4 2 00GB5s Gritblast 53022(II)/53039 6321 0 

GB1w Gritblast 53022(II)/64159 64222GB2w Gritblast 53022(II)/64159 6 3 2 00GB3w Gritblast 53022(II)/64159 6 4 2 00GB4w Gritblast 53022(II)/64159 7311 0 

GB5w Gritblast 53022(II)/64159 53311 

P1s Spray Zn Phosphate 53022(II)/53039 96532P2s Spray Zn Phosphate 53022(II)/53039 96433P3s Spray Zn Phosphate 53022(II)/53039 95422P4s Spray Zn Phosphate 53022(II)/53039 95433P5s Spray Zn Phosphate 53022(II)/53039 86433

P1w Spray Zn Phosphate 53022(II)/64159 95322P2w Spray Zn Phosphate 53022(II)/64159 95322P3w Spray Zn Phosphate 53022(II)/64159 96422P4w Spray Zn Phosphate 53022(II)/64159 96433P5w Spray Zn Phosphate 53022(II)/64159 87533

C1s Cheminhib 420 53022(II)/53039 74311 

C2s Cheminhib 420 53022(II)/53039 74211 

C3s Cheminhib 420 53022(II)/53039 6421 0 

C4s Cheminhib 420 53022(II)/53039 54322C5s Cheminhib 420 53022(II)/53039 6 3 2 00

C1w Cheminhib 420 53022(II)/64159 6 4 000C2w Cheminhib 420 53022(II)/64159 54322 C3w Cheminhib 420 53022(II)/64159 6532 0 

C4w Cheminhib 420 53022(II)/64159 6322 0 C5w Cheminhib 420 53022(II)/64159 64311 

WP1 DoD-P-15328 53022(I)/46168 No Data No Data No Data No Data No Data WP2 DoD-P-15328 53022(I)/46168 No Data No Data No Data No Data No Data WP3 DoD-P-15328 53022(I)/46168 No Data No Data No Data No Data No Data WP4 DoD-P-15328 53022(I)/46168 7622 No Data 

WP5 DoD-P-15328 53022(I)/46168 No Data No Data No Data No Data No Data 
25

Figure 20. 53022(II)/53039A at 80 cycles GM 9540P cyclic corrosion. 
26

Figure 21. 53022(II)/64159 at 80 cycles GM 9540P cyclic corrosion. 
27

Figure 22. Legacy coating system (a) vs. current coating systems (b and c) pretreated with spray 

zinc phosphate at 80 cycles GM 9540P cyclic corrosion. 
28

Figure 23. Initial appearance of bare pretreated specimens prior to 100% relative humidity 

exposure. 
29

Figure 24. Appearance of bare pretreated specimens after 16 hr of ASTM D 1735 100% relative 

humidity exposure.
30

Figure 25. Initial appearance of bare pretreated specimens prior to 1 week of 27 °C, 69% 

relative humidity ambient laboratory exposure. 
31

Figure 26. Appearance of bare pretreated specimens after 1 week of 27 °C, 69% relative 

humidity ambient laboratory exposure. 
32

panels. Of these panels, the CHEMINHIB 420 treated abrasive blast panels had the least amount 

of rusting among the four surface pretreatments with most of the rusting occurring within the 

surface pores commonly found on 46100 steel. Surprisingly, despite the initial head start in flash 

rust, there was less rusting present on the KLEENINHIB 486 prepared spray zinc phosphate 

panels after 16 hr vs. the standard Henkel-cleaned spray zinc phosphate panels. For the 

laboratory-exposed panels, there was no significant visible damage to any panels except for the 

panels prepared with only abrasive blast that only showed localized flash rusting. 

3.4 Rising Step Load (KIEAC) 

Figure 27 shows the average KIEAC value for each alloy/pretreatment configuration plotted with 

respect to notch orientation. The complete listing of all KIEAC values, details, and the crack 

initiation loads are listed in table 10. It can be seen that experimental results fall within the 

historic ranges of the respective alloys without a protective pretreatment. As expected, MIL-A46100D performed better than the VAR 4340. It was also expected that, for all samples tested, 

L-T orientations would be more resistant to environmentally assisted cracking than T-L 

orientations. While the L-T wash primer 46100 samples had a highest average KIEAC, it was only 

5% higher than its T-L counterpart. Moreover, the reverse was true of the phosphated 46100 

where the KIEAC for the T-L orientation was 4% higher than the L-T. These results show no clear 

trend to confirm that either orientation is more resistant to EAC than the other. In addition, there 

is no evidence to suggest that either spray zinc phosphate or DOD-P-15328D wash primer had an 

adverse influence on the KIEAC of either 46100 or 4340. 

4. Discussion 

The goal of this study was to investigate alternative pretreatments for hexavalent chromium 

based DOD-P-15328D wash primer. Due to the less aggressive nature of the current GDLS 

surface preparations, most of the discussion will concern the proposed spray zinc phosphate 

process. It is the aqueous nature of the spray zinc phosphate application process that provides 

questions as to the possible risk for EAC. During early production of the U.S. Marine Corps 

Light Armored Vehicle (LAV) at the London, Ontario facility (formerly GM Defense) that is the 

current site for Stryker production, there were numerous problems with EAC in the 46100 armor 

plate, notably the hatch covers and doors. The typical areas of crack nucleation were near the 

edges where cuts had been made. A previous U.S. Army Materials Technology Laboratory 

(MTL) investigation revealed that most of this damage from cracking could be avoided by 

changing the method for cutting the armor plate. MTL recommended a change from underwater 

plasma arc cutting to laser cutting techniques. By using laser cutting, the thicknesses of the 

remaining untempered martensite layer and the heat affected zone at the cut were significantly 

reduced (31). After implementing the MTL recommendations, the cracking problems were 

greatly reduced. In addition to these improvements, the enhanced precision inherent with the 
33

Figure 27. Average KIEAC for pretreated 4340 and 46100 by orientation. 

laser cutting improved the overall fit of individual armor plate components and significantly 

reduced the preloading induced at subsequent joining stages. Despite these significant 

production improvements, the risk for EAC remains a concern for Stryker fabrication, especially 

for any process or situation that when introduced could cause an influx of hydrogen. 

Among the alternative pretreatments investigated, the hydrogen ions in the phosphoric acid 

component present in the Henkel spray zinc phosphate process remains the key area of concern. 

Before the procedures that investigated sensitivity to EAC on phosphated high hard are 

discussed, it should be noted that the DOD-P-15328D wash primer pretreatment coatings, used 

extensively on LAV’s and on early production Stryker vehicles, also contained phosphoric acid. 

In addition, the CHEMINHIB 420 and KLEENINHIB 486 surface preparation stages currently 

used in conjunction with abrasive blast at the GDLS London facility and at the Militex 

subcontracted facility both are water soluble solutions for cleaning and inhibitor purposes. Any 

of these “wet” preparation stages listed represent varying degrees of vulnerability to hydrogen 

infiltration. The proposed zinc phosphating method, like the wash primer, is a spray process so 

the risks for hydrogen influx in spray application versus immersion methods for phosphating are 

likely to be inherently diminished. Another decrease in spray zinc phosphate risk comes from 

the recently revised Federal Specification TT-C-490D allowing the use of nonchromate final 

rinses; this eliminates hexavalent chromium based chromic acid, another potential source of 

hydrogen. 

For the spray zinc phosphate sprayed rising step load EAC specimens there was no significant 

drop in KIEAC vs. the DOD-P-15328D wash primer treated specimens for either the L-T or T-L 

orientations. All values were within the KIEAC historic range for 46100 high hard steels. Spray
34

Table 10. Experimental conditions and KIEAC values for rising step load specimens. 

Sample 

ID 

Sample 

Material 

Sample 

Orientation 

Hardness 

Rc

Surface 

Pretreatment 

Crack 

Initiation 

Load Pu 

(lb) 

KIEAC

(ksi√in) 

Pretreatment 

Applied 

Before/After 

Precracking 

715064 4340 TL 50.8 Spray zinc 

phosphate 

52.4 15.1 After 

715057 4340 LT 50.9 Spray zinc 

phosphate 

54.2 15.7 After 

715038 46100 LT 50.7 Spray zinc 

phosphate 

70 19.5 After 

715037 46100 LT 50.4 Spray zinc 

phosphate 

68 19.1 After 

715042 46100 LT 51 Spray zinc 

phosphate 

59 17.6 Before 

715048 46100 TL 51.4 Spray zinc 

phosphate 

79.5 22.5 After 

715047 46100 TL 51.1 Spray zinc 

phosphate 

62.9 18.0 After 

715051 46100 TL 51.1 Spray zinc 

phosphate 

58 16.6 Before 

715043 46100 LT 51.4 DOD-P-15328D 71.4 20.4 After 

715053 46100 TL 51.2 DOD-P-15328D 68.2 19.1 After 

715054 46100 TL 51.2 DOD-P-15328D 68.9 19.9 After 

Note: Rockwell C hardness values were averaged from three readings per specimen. 

zinc phosphate that was applied to precracked samples even appeared to impart more EAC 

resistance than when the spray zinc phosphate was applied prior to precracking. As seen in 

table 10, regardless of orientation, the phosphate applied to precracked samples had on average, 

~16% higher KIEAC values. One possible explanation is that during the application process, 

phosphate may have penetrated into the precrack and thus provided the additional EAC 

resistance. Despite these interesting results, more tests with a larger statistical sampling would 

be necessary to validate this observation. 

Results for coating adhesion for spray zinc phosphate as well as the abrasive blast and abrasive 

blast with CHEMINHIB 420 were significantly higher as well as more consistent than results for 

DOD-P-15328D. Coating adhesion performance should improve regardless of which of the 

wash primer alternatives is selected. 

A key area of interest for surface pretreatments is the processing in the production environment. 

Currently abrasive blasting for the GDLS London plant is done off-facility at Militex, a local 

subcontractor responsible for cleaning and mechanical surface preparation and also a portion of 

the MIL-P-53022-10 primer coating application. The vehicles that are not primer coated at 

Militex receive an additional KLEENINHIB 486 water soluble cleaner/inhibitor process step in 

preparation for the interim transit period before the primer application at the GDLS facility. The 

processes as they stand currently are quite simple, figures 2–4 highlight differences between the 
35

surface preparation and pretreatment stages conditional to the location of primer application as 

well as include the Henkel Bonderite spray zinc phosphate steps. In addition to introducing 

several more surface preparation stages, the pot temperatures on three of the Bonderite chemical 

spray steps must be heated to within a specified range. Additional care must be taken by the 

process personnel to control the Bonderite 952 stage with respect to “free acid” and “total acid” 

through a series of quality control inspections via titrations as specified in the Henkel Technical 

Process Bulletin. When the free acid levels were elevated, more orange-brown staining occurred 

on the zinc phosphated panels at the PARCOLENE 99 rinse stage. This staining was present in 

varying degrees for all of the spray zinc phosphated test panels that were prepared. 

Specifications TT-C-490 and MIL-DTL-16232G (32) for phosphating both mention the 

acceptability of these stains. Despite these stains, the zinc phosphate treated panels performed 

well in corrosion resistance and adhesion suggesting that zinc phosphating is somewhat forgiving 

from a process control standpoint and that the specification allowance for some staining appears 

to be reasonable. Through optimizations to free acid and total acid levels and periodic 

inspections to check the zinc phosphate coating weight vs. the specifications, the quality and 

appearance of the phosphate coating can be optimized as seen in figure 28. 

If spray zinc phosphating is implemented in production as the pretreatment step before primer 

application, additional steps can be taken to reduce the risk for EAC. Phosphating specifications 

TT-C-490, MIL-DTL-16232G, and a previous phosphating study (33) all include instructions for 

hydrogen embrittlement heat treatment. Heat treatment schedules found in these publications 

consist of ageing at room temperature and should be executed before any loading of the material 

is permitted. The room temperature dwell times recommended differ between the specifications 

at 120 and 240 hr, respectively, for MIL-DTL-16232G and TT-C-490. Although the ageing 

period in MIL-C-16232G is shorter, this specification also includes a quality control test to 

determine the adequacy of the hydrogen embrittlement relief. The specification recommends 

periodic checks at intervals of 90–120 days in a production environment to ensure that the 

hydrogen embrittlement relief remains adequate. 

Regardless of what pretreatment method is implemented, every attempt should be made 

throughout all stages of production to limit and relieve possible residual tensile stresses in the 

46100 at locations such as welds or where cold working and/or machining has occurred. The 

manufacturing improvements made during previous LAV production cycles have done much to 

limit these residual stresses. Additional guidelines for residual stress relief as it applies to 

phosphating are also available in MIL-DTL-16232G. 
36

Figure 28. Changes in phosphate quality/appearance from adjustments to free acid 

concentration point values via increases of Henkel Primer 40 to the BONDERITE 

952 spray zinc phosphate solution. 
37

5. Conclusions 

1. Spray zinc phosphate pretreatment improved the creepback resistance for CARC coated 

MIL-A-46100D high hard armor steel for both ASTM B 117-90 neutral salt fog and GM 

9540P cyclic corrosion. 

2. Coating adhesion for spray zinc phosphate pretreatment vs. abrasive blasting alone was 

marginally lower, but was still significantly improved when compared to DOD-P-15328D 

wash primer. 

3. PPG CHEMINHIB 420 water soluble flash rust inhibiting coating did not degrade adhesion 

of the MIL-P-53022-10 (type II) primer to the substrate vs. substrates that were prepared 

with only abrasive blasting. 

4. PPG CHEMINHIB 420 water soluble flash rust inhibiting coating greatly increased 

resistance to flash rusting when applied to abrasive blasted panels. 

5. If spray zinc phosphating is not used as a pretreatment after abrasive blasting, the continued 

use of PPG CHEMINHIB 420 over abrasive blasted surfaces is recommended. 

6. The results of the rising step load tests, indicate that spray zinc phosphate had no adverse 

effect on the KIEAC for MIL-A-46100D high hard armor. 

7. When spray zinc phosphate is used, quality control and inspection procedures in 

accordance with MIL-DTL-16232G for hydrogen embrittlement relief should be followed. 
38

6. References 

1. Gibb, H.; Lees, P.; Pinsky, P.; Rooney, B. Lung Cancer Among Workers in Chromium 

Chemical Production, American Journal of Industrial Medicine 2000, 38, (2), 115–126, 

published online. 

2. MIL-A-46100D (w/Amendment 1). Armor Plate, Steel, Wrought, High-Hardness. 

U.S. Department of Defense: Washington, DC, June 1990. 

3. DOD-P-15328D (Note 1). Primer (Wash), Pretreatment (Formula No. 117 for Metals). 

U.S. Department of Defense: Washington, DC, March 1992. 

4. TT-C-490D Federal Specification. Chemical Conversion Coatings and Pretreatments for 

Ferrous Surfaces (Base for Organic Coatings). General Services Administration: 

Washington, DC, July 2002. 

5. CHEMINHIB 420. Water Soluble Short Term Corrosion Protective Coating—Product Data 

Sheet. PPG Industries, Inc.: Euclid, OH, May 1996. 

6. Bruce, C. Hydrogen Damage. Metals Handbook Ninth Edition, 13, p 168. 

7. MIL-P-53022-10. Primer, Epoxy Coating, Corrosion Inhibiting, Lead and Chromate Free. 

U.S. Department of Defense: Washington, DC, February 1992. 

8. MIL-C-53039A. Coating, Aliphatic Polyurethane, Single Component, Chemical Agent 

Resistant. U.S. Department of Defense: Washington, DC, May 1993. 

9. MIL-DTL-64159. Coating, Water Dispersible Aliphatic Polyurethane, Chemical Agent 

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