BUILDING SCIENCE SERIES

U.S. DEPARTMENT OF COMMERCE / National Bureau of Standards

ililiMI mm

i
The Building Science Series

("he Building Scieiu-c Series disseminates technical information developed at the National Bureau of Standards on

building materials, components, systems, and whole structures. The Series presents research results, test methods, and performance criteria related to the structural and environmental functions and the durability and safety characteristics of building elements and systems. These publications, similar in style and content to the NBS Building Materials and Structures Reports (1938-59),

are directed toward the manufacturing, design, construction, and research segments of the building industry, standards organizations, and oflficials responsible for building codes. The material for this Series originates principally in the Center for Building Technology of the NBS Institute

for Applied Technology. The publications are divided into three general groups: Building Systems and Processes;

Health, Safety and Comfort; and Structures and Materials. For further information regarding these publications

please contact the Scientific and Professional Liaison Section, Center for Building Technology, Institute for Applied Technology, National Bureau of Standards, Washington, D.C. 20234.

[See mailing list announcement on last page J
i^PR 1 1 1975

The Adherence of Porcelain Enamel

to Aluminum

Margaret A. Baker

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20234

Sponsored by the Porcelain Enamel Institute 1911 North Fort Myer Drive

Rosslyn, Arlington, Va 22209

U.S. DEPARTMENT OF COMMERCE, Frederick B. Dent, Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts, Director

Issued Novetnber 1974
Library of Congress Cataloging in Publication Data

Baker, Margaret A. The adherence of porcelain enamel to aluminum.

(National Bureau of Standards Building Science Series 59) Supt. of Docs. No.: C13.29/2:59

1. Enamel and Enameling. 2. Aluminum Coatings.

3. Adhesion. I. Porcelain Enamel Institute. II. Title.

III. Series: United States. National Bureau of Standards. Building Science Series 59. TA435.U58 No. 59 [TS700] 690'.08s [620.1'46] 74-23734

National Bureau of Standards Building Science Series 59

Nat. Bur. Stand. (U.S.), Bldg. Sci. Ser. 59, 45 pages (Nov. 1974) CODEN: BSSNBV

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1974
ABRIDGED GLOSSARY

1. Adherence: The ability of an enamel to stay on the metal after firing.

2. Diffusion Zone: An area between the porcelain enamel and the aluminum alloy that

contains constituents of both the enamel and the alloy.

3. Reaction Product: An element or compound formed as a result of reaction between the

enamel and the metal.

4. Spalling: The flaking or chipping of the enamel from the metal. In this paper,

spalling is the result of exposure to a chemical or natural weathering environment,

not of 'mechanical damage.

5. Porcelain Enamel: A glass coating that is fused to a metal at temperatures of 900°F

or higher. In this paper "enamel" and "porcelain enamel" will be used interchangeably.

6. Frit: The basic glass used in the porcelain enamel.

7. Mill Additions: Opacifiers, coloring oxides, and suspending media that are added to the frit to give the porcelain enamel the desired finished appearance and to make

it easy to apply to the base metal.

8. Firing: The heating of the metal and applied enamel to fuse the enamel to the metal.

9. Transmission Electron Microscopy: A beam of electrons is passed through the specimen

being studied. Differences in the absorption of the electrons are shown on a fluorescent screen or photographic film.

10. Replica Electron Microscopy: The same as transmission electron microscopy except a replica is made of the surface to be studied which eliminates the need for preparing

extremely thin specimens.

11. Scanning Electron fticroscopy: A beam of electrons is reflected off the surface being

studied. This enables one to study thick specimens without preparing replicas.

12. Electron Microprobe: The specimen is bombarded with an electron beam, which causes

it to emit X-rays characteristic of the elements present. These X-rays are either

displayed to give a qualitative indication of the distribution of the element or they can be calibrated to give a quantitative distribution of the element.

13. X-ray Powder Diffraction: The material to be studied is finely ground (powdered)

and then irrldated with X-rays from a given source. The elements present in the

powder can then be identified by their characteristic peaks.

iii

METRIC/CUSTOMARY UNIT CONVERSIONS

A. Temperature

1000°F 538°C

960°F 516°C

940°F 504°C

275°F 135°C

170°F 77°C

100°F 38°C

B. Weight

2000 lbs. 908 Kg

C. Length

Angstroms 1 x 10 meters

Inch 2.54 centimeters

V
TABLE OF CONTENTS

Page

1. Introduction 1

2. Background Information 2

2.1 Base Metal 2

2.2 Enamel 2

2.3 Metal Pretreatment 2

2.4 Firing 3

3. Discussion of Research Techniques 3

3.1 Chemical Spall Testing 3

3.1.1 Effects of Pretreatments , Enamel, Alloy or Alloying

Constituents on Spall Resistance 4

3.1.2 Spall Testing Deformed Specimens 5

3.1.3 Effect of Humidity on Spall Resistance of Specimens 5

3.2 Analyses of Spall Test Solutions 6

3.3 Oxide Layer 6

3.4 Light Microscopy 7

3.5 Electron Microscopy 8

3.6 Electron Microprobe 8

3.7 X-ray Powder Diffraction 9

3.8 PEI Adherence Tester 9

3.9 Direct-Tension Pulling Tests ^

4. Theory for the Retention of Adherence of Porcelain Enamel to Aluminum 10

5. Round-Robin Testing of 6063 Alloys :. 10

6. Summary of Techniques and Findings Used in Studying the Mechanisms of

Adherence of Porcelain Enamel to Aluminum 11

7 . Acknowledgment 12

8. Bibliography of Previous Reports of This Study 14

vi
The Adherence of Porcelain Enamel to Aluminum

Margaret A. Baker

Light and electron microscopy, electron microprobe, and X-ray diffraction techniques were used to determine the mechanisms of adherence of porcelain enamel to aluminum. A

theory is presented that adherence depends upon diffusion of aluminum into the enamel and

further, the diffusion zone should be relatively free of reaction products for the enamelmetal system to retain good adherence after exposure to chemical solutions or to weathering.

Round-robin testing of 6063 aluminum alloy extrusions indicated that this alloy can be

enameled if care is exercised in the selection of the enamel and the pretreatment

.

Key words: Adherence; aluminum; electron microprobe; electron microscope; porcelain

enamel; spalling; X-ray diffraction.

INTRODUCTION

The Porcelain Enameled Aluminum Council of the Porcelain Enamel Institute (PEI)

initiated a Research Associateship program at the National Bureau of Standards (NBS) in

1966 to study the mechanisms of adherence of porcelain enamel to aluminum. An understanding

of adherence is important because spalling (or flaking of the enamel from the aluminum

alloy some time after the finished product has been placed in service) is the primary

technical problem facing the porcelain enameled aluminum industry.

It was felt that if the mechanisms of adherence and spalling were understood, then more of the commercially available aluminum alloys might be porcelain enameled. It would

be beneficial to producers of porcelain enameled aluminum products if the aluminum alloys

for porcelain enameling did not have to be specially ordered from the primary metal

suppliers or if lighter gages of the higher strength aluminum alloys could be porcelain

enameled without subsequent spall failures.

This 7 year research program is unique in that the research work was carried out in

the laboratories of four cooperating aluminum companies and one frit company (see

acknowledgment. Section 7) as well as the laboratories at NBS.

This report summarizes the avenues investigated and presents a theory for the

adherence of porcelain enamel to aluminum. It also summarizes round-robin testing made

to determine whether porcelain enamel could be successfully applied to 6063 aluminum

alloy. This alloy was chosen because of its wide availability from both primary and

secondary suppliers and its "easy squeeze" extrusion properties making it an ideal metal

for such applications as window frames and door jambs.

This report contains 8 sections. Section 1 contains only general introductory

information. Section 2 contains background information on base metal and enamel

compositions, pretreatments and firing times for the enamel-metal systems studied.

Section 3 describes research methods used to investigate the adherence of the enamel to the metal and the discussion of the results obtained. Section 4 puts forth a theory for

the adherence of porcelain enamel to aluminum. Section 5 contains the results of the

round-robin testing and Section 6 provides a summary of the findings resulting from this

7 year research program. Section 7 contains an acknowledgment to those companies that

contributed to this program and Section 8 is a bibliography of reports on this project.-

1
The base metal and enamel compositions or the pretreatment and firing data for the

enamel-metal systems included in the round-robin tests are not reported in Section 2 because the processing of these specimens was done in commercial plants using proprietary

procedures. Occasionally, in Section 3, the laboratories conducting the studies are referred to as laboratory A, B, C, etc. These designations refer either to the laboratories

at NBS or to the research laboratories at one of the four aluminum companies or of the

frit company cooperating in this work.

2. BACKGROUND INFORMATION

2.1 Base Metal

A total of 12 aluminum and a high purity magnesium alloys was used in the program.

The four alloys initially selected for study included two relatively pure alloys, 1199 and

1100, and two magnesium bearing alloys, 5257 and 5657. When the aforementioned alloys

did not produce an enamel-alloy system that spalled readily, a magnesium silicide alloy,

6061, and two high magnesium alloys, 5154 and 5086, were added. The compositions of these

alloys are given in table 1.

Occasionally, 3003, 5053 and 6063 alloys have been studied in this work. The

composition of the 6063 is given in table 1 but the exact compositions of 3003 and 5053 were not known. Also, the initial lots of 6061 and 5086 have been depleted so the metal

used toward the end of this program may vary slightly from the composition given in table 1.

Super purity alloys (1199) with the additions of 1% Mg2Si and 2% Mg were added late

in the program. The composition of these alloys is also given in table 1. High purity

magnesium was used for a study of the enamelability of magnesium and the rate of solution

of magnesium oxide by the enamel. Unless otherwise noted, all specimens were 3x6 inch

rectangles cut from sheet stock.

2.2 Enamel

The basic enamel used was a tan enamel with an AL-2* frit. The oxide composition of

the fired enamel, including the frit and mill additions, is given in table 2.

There have been four variations of 'this enamel. The variation used most often has

been designated "basic white lead-silicate enamel". This enamel had titania substituted

for the coloring oxide in the mill addition. The oxide composition of the frit (AL-2) used

in the "basic white lead-silicate enamel" is given in table 3.

The other three variations are designated "alumina-rich", "silicate-rich", and

"magnesia-rich". These variations were produced by substituting alumina, silica, or magnesia respectively for the titania in the mill addition. The spall test results of the

enamels did not warrant the determination of their fired compositions.

In addition to these four variations of the basic enamel, two special enamels were

prepared for this test program. These were designated "Lead-Free" and "Silica-Free"

enamels. The oxide compositions of the frits used in these special enamels are also

presented in table 3.

2.3 Metal Pretreatment

The metal was prepared for enameling by one of the following pretreatments

:

1. Prefiring: The metal is heated at 1000°F for ten minutes prior to enameling.

2. Chemical Cleaning: The metal is subjected to a hot buffered alkaline

cleaner before enameling.

*The AL-2 number indicates to industry members which of the many commercially available

frits was used.

2
3. Pickling: The metal is subjected to the chemical clean plus a hot acid

chromate deoxidizer, and an alkaline-chromate bath before enameling.

Pickling as described above is the preferred pretreatment used in the

industry to produce enameled 6061 alloy with good spall resistance.

4. Anodizing: The aluminum is anodized in sulfuric acid before enameling.

5. Vapor Deposition: A few of the alloys were prepared for enameling by

washing with acetone and vapor depositing a thin layer of metal.

These pretreatments will be referred to as prefired, chemical clean, pickled,

anodized or vapor deposited , where the blank will be filled in with the metal

deposited.

2.4 Firing

The basic enameling firing cycle was ten minutes at 1000°F. However, the firing

cycle was varired by extending the firing time at 1000°F, to 30, 90, 300, 480, 600, and

1080 minutes or by lowering thefiring temperature to 960 and 940 °F for 10 minutes. To avoid possible confusion about firing conditions, the firing time and temperature will

be given in further discussions, tables and figures. If the firing time and temperature

are°not given, they will be ten minutes at 1000 °F. Except for the enamels in the roundrobin tests, the firing was done in electrical laboratory furnaces.

The furnace atmosphere was varied from air at 760 mm Hg pressure to air at 193 mm Hg,

nitrogen at 193 mm Hg, hydrogen (35%) - argon (65%) at 193 mm Hg, oxygen at 193 mm Hg,

argon at 193 mm Hg, nitrogen at 0.003 mm Hg, and a mixture of nitrogen at 163 mm Hg plus

30 mm water vapor for the resulting atmosphere (nitrogen plus water vapor) at 193 mm Hg

pressure. The furnace was also operated at 760 mm pressure with oxygen flowing through

it during the firing cycle. Water was also added to asbestos mats placed in the furnace

in amounts varying from 0 to 200 cc. This was thought to simulate changes in industrial

furnaces atmospheres as the amount of ware through the furnace is increased.

3. DISCUSSION OF RESEARCH TECHNIQUES

3.1 Chemical Spall Testing

There are two standard chemical spall tests used in the porcelain enameled aluminum ' industry. For one test the specimen is immersed in a 5 percent ammonium chloride solution

for 96 hours while for the other the specimen is immersed in a one p'ercent antimony

trichloride (SbCl^) solution for 20 hours. There is no mechanical stress applied in either

test. A specimen fails as a result of these chemical tests when the enamel flakes from

the edge in pieces at least one inch long by 1/8 inch wide or if it spalls from the

interior surface in areas at least 1/8 inch in diameter.

All specimens prepared for use in this program were spall tested in antimony trichloride

and a summary of the general spall-resistance data is given in table 4. Since the measured

spall resistance of a specific enamel-metal system may vary from specimen to specimen, the

spalling behavior of a particular set of specimens will usually be presented with the

results of other tests in this report. Some additional spall tests using distilled water

and ammonium chloride were also run.

The reactions that occurred between prefired and enameled 5154 and the antimony

trichloride spall test solution were observed with slow motion photography. Later viewing

of this film indicated that reactions occurred almost immediately - gassing and bubbling

were much in evidence, a black precipitate was formed on the aluminum surface and tended

to concentrate near the enamel-metal interface. A white gelatinous material also appeared

to form near the enamel-metal interface. The pressure caused by these reactions at the

interface apparently caused the enamel to spall. The time required for these reactions

to cause spalling was less than five minutes.

3
Additional studies of the action of an-timony trichloride on polished sections of

number 6061 alloy indicated that the SbCl^ spall test solution attacked the aluminum at specific sites, such as at certain Mg^Si and at aAlFeSi particles and at certain grain

boundaries

.

3.1.1 Effects of Pretreatments , Enamel, Alloy or Alloying

Constitutents- on Spall Resistance

The following studies were conducted to determine how a special pretreatment

,

enamel, alloy, or alloying constituent affected the spall resistance of a particular

enamel-metal system:

1. The effect of vapor deposition of metals on spall resistance of

various alloys.

Magnesium was vapor deposited on number 1100 alloy, prefired and then enameled.

All specimens of 1100 with vapor-deposited magnesium spalled during the spall tests.

The greater the amount of magnesium deposited on the specimen, the greater the

spalling. When chromium was vapor deposited over the previously vapor-deposited

magnesium on the resulting enamel-metal system had excellent spall resistance.

Improved spall resistance was noted when chromium was vapor deposited on number

5086 alloy (which contains about 4 percent magnesium). However, the enamel still

spalled enough to constitute failure. Vapor-deposited copper and iron also improved

the spall resistance of 5086 but not as much as chromium.

2. The effect of the distribution of magnesium silicide on the spall resistance

of number 6063 alloy.

Four sets of duplicate specimens of 6063 alloy were heat treated to put its

magnesium disilicide component into four forms: solid solution, submicroscopically

precipitated, coarsely precipitated, and very coarsely precipitated. These

specimens were then pickled, enameled and spall tested. There was some variation

between the duplicate specimens, but the specimens with the coarsely precipi<"ated

Mg2Si exhibited the most spalling in both specimens while the submicroscopically

precipitated Mg2Si consistently showed good spall resistance. The specimens with

the other two forms of Mg2Si showed variable results between these two extremes.

These results indicate that the particle size of Mg2Si may affect the enamel's

spall resistance, possibly due to the ability of pretreatments to remove Mg2Si

from the surface of the specimen.

3. The spall resistance of magnesium.

High purity magnesium was enameled after various pretreatments. The spall

resistance of these specimens is summarized in table 5. It was surprising that

any of these passed the spall test, since magnesium appeared to make aluminum have

poor spall resistance.

4. Spall resistance of silica-rich, alumina-rich, and magnesia-rich enamels.

Silica, alumina and magnesia were substituted respectively for the titania in

the mill addition of the basic tan enamel. When these enamels were applied to prefired 3003, they showed excellent spall resistance except for the magnesium-rich

enamel, which showed some small interior spalling,

5, Spall resistance of silica-free, lead-free and basic white lead-silicate

enamels

.

4
Spall test results on a special set of silica-free and lead-free enamels

applied to 1199, 1199 with 2% Mg, 1199 with 1% Mg2Si, and 6061 were compared with

the spall test results for the basic white lead-silicate enamel applied to these

same metals. These results are presented in table 6. It will be noted that all

the silica-free enamels are listed as having spalled completely. Actually, thes^

enamels were dissolved by the antimony trichloride test solution since there was

no glassy residue remaining in the test solution.

6. Spall resistance of enamels fired with increasing amounts of water in the

furnace atmosphere.

Water in amounts varying from 0 to 200 cc was added to the furnace atmosphere

in which the standard enamel was fired on pickled 5086 and 6061. These specimens were

then spall tested and sectioned. All the enameled 6061 specimens passed the spall

test while all the enameled 5086 specimens failed. There was no marked difference

in the cross-sections of each alloy as the amount of water added was increased.

3.1.2 Spall Testing Deformed Specimens

Industry members of the Aluminum Council reported that spall testing enameled

specimens after deforming them over a mandrel gave a better correlation between laboratory

spall resistance tests and field experience than spall tests on undeformed enameled

specimens. Therefore, a mandrel with radii varying from 1/8 to 7 inches was designed

and used in preparing a new set of specimens for spall testing. One half of the 3 x 9-inch

specimens were deformed over the mandrel before testing and the other half were tested flat

as control specimens. The spall test results on the deformed and flat specimens were

similar (see table 7). However, minor differences in spall resistance were readily apparent

on the deformed specimens but were not noticed on the flat specimens. It is possible that the

time required to run a spall test could be reduced if deformed specimens were used.

3.1.3 Effect of Humidity on Spall Resistance of Specimens

The Aluminum Council members also reported cases of spalling after exposure to high

humidity. The first investigation of spalling caused by humidity consisted of exposing

prefired and enameled 5086 to 100 percent relative humidity at 100°F. After four months

exposure to these conditions, no spalling had occurred. Then the water was inadvertently

turned off, the humidity dropped and the temperature rose to 275°F. This change in test conditions caused the enamel to spall severely. Other attempts to produce this type of

spalling on prefired 5086 alloy with shorter exposure times included:

1. Exposure to 100 percent relative humidity for 48 hours at 100°F followed by

exposure in an oven at 275°F for 24 hours. This resulted in slight spalling after

three cycles. After six cycles, no additional spalling had occurred.

2. Immersion in distilled water at room temperature for 48 hours followed by

exposure in an oven at 275 °F for 24 hours. This resulted in a very small amount of

spalling after the third immersion-dry cycle and slight additional spalling after

the 6th cycle,

3. Total immersion in hot (170°F) distilled water for 24 hours followed by

12 hours dry at 275°F in an oven. This resulted in spalling during the hot water

part of the first cycle. Some additional spalling occurred during the second

cycle. A further cycle did not yield any more spalling. This method gave the

most spalling of all the five methods tried, but it was not as severe as had

occurred on the long term humidity exposure which prompted this work.

4. Suspension for 24 hours (with accompanying condensation) of the samples over

an enclosed water bath with the water temperature at 170°F. This was followed by a 12-hour drying cycle at 275 °F in an electric oven. This test was run for four cycles

with no spalling.

5
and one hour dry. This was run continuously for seven weeks with no spall

failures occurring.

3.2 Analyses of Spall Test Solutions

Spent spall solutions for three spall test methods were analyzed to gain insight into

reactions that result in spalling. A qualitative analysis of distilled water, airraionium chloride and antimony trichloride spall solutions after prefired specimens of 1100, 6061,

and 5086 alloys had been tested revealed that the spent spall solutions contain appreciable

amounts of magnesium when spalling occurred. This analysis also indicated that manganese,

lead, silicon, and titanium also appeared in the spall solutions after spalling had occurred

(see table 8 for a summary of these test results)

.

Quantitative analyses of the spent antimony trichloride spall solutions, after samples

of prefired 1100, 6061, and 5086 had been tested showed that the solution in which the 1100

was tested contained 0.3 mg of magnesium, that from the 6061 contained 31 mg, and that from

the 5086 contained 165 mg. The relative amounts of magnesium in the spall solutions

correlated fairly well with the amount of spalling observed on the enameled samples. For

that reason another quantitative analysis for magnesium and chromium (chromium is used in

pickling and is thought to tie up the magnesium) was made using both pickled and prefired

1100, 3003, 6061, and 5086 in distilled water, ammonium chloride, and antimony trichloride

spall test solutions. The spall solutions were also analyzed after prefired and pickled

metal blanks (without enamel) were tested. A summary of these results is presented in

table 9. Although these results again indicated an increase in magnesium with increased

spalling, determinations of the unenameled metal blanks indicated a similar increase.

When the values for the blanks (either for 100 percent bare metal or corrected by

multiplying by the percentage spalling which occurred on the specimens) were subtracted

from the values for the enameled samples there was no consistent increase in the chrome

or magnesium content of the spall test solutions for the enamel-metal systems that spalled.

3.3 Oxide Layer

The oxide layers that form naturally on aluminum alloys after normal exposure to the

atmosphere have been investigated in regards to thickness, composition and dissolution

by the enamel.

The thickness of the naturally occurring oxide and the oxide layer resulting from a ten minute prefire were determined by three of the aluminum companies. Two of the

companies measured the thickness of the oxide layer after removing it from the metal by

dissolving the metal, while the third measured it in situ. The in situ determinations

appeared to be affected by the base metal and are not included in the results in table 10.

The magnesium content of the naturally occurring oxide layer and the oxide layer

formed during prefiring were measured by two laboratories. The magnesium content of the

oxide layer was found to increase markedly as the magnesium increased in the alloys.

These results are presented in table 11.

Since the naturally occurring oxide films and the prefired oxide films are extremely

thin and difficult to measure, thick oxide films were formed by anodizing to study the

behavior of the oxide films during enameling and firing. Although the thickness of the

anodizing was varied, certain trends were evident. About 5000 angstroms of the oxide on the high-purity aluminum alloys were taken into solution by the enamel while the oxide

layer on alloys containing magnesium or manganese remained the same or increased during

enameling and firing as illustrated in table 12. Since magnesium is the main alloying

constituent in alloys that are difficult to enamel, pure magnesium was also anodized and

enameled and, surprisingly, the pure magnesium (or magnesium oxide) was also taken into

solution by the enamel.

6
3.4 Light Microscopy

Light microscopy, one of the original analytical tools used in metallurgy, has been

used both to monitor the preparation of specimens for examination by the electron microscope

and electron microprobe and to observe the microstructure of many enamel-metal systems.

The observations with the light microscope include studies of the effect of different

pretreatments on Mg2Si, Mg^Al^, aAlFeSi and FeAl second phase constituents of these alloys.

These studies indicated 1) the enamel by itself attacked only Mg Si, 2) the hot acid

chromate deoxidizer plus enamel severely attacked the Mg Si and Mg^Alo and slightly attacked

the aAlFeSi and FeAl^, 3) the hot acid chromate deoxidizer followed by the alkaline chromate

and enameling attacked the Mg^Si and Mg Ai about the same as the hot acid chromate and

enameling but the aAlFeSi and FeAl^ appeared to be protected from attack by the addition

of alkaline chromate, and 4) alkaline chromate and enameling showed only slight attack on the Mg^Si and Mg^Alg and no attack on the aAlFeSi or FeAl^.

A series of photomicrographs taken with polarized light showed an interesting

difference between specimens that spalled and those that did not spall. The photomicrograph

of prefired, enameled 5154 (which spalled badly) showed a continuous black layer between

the enamel and the metal. The photomicrograph of prefired, enameled 6061 (which also

spalled, but not as badly as the prefired 5154) showed a black layer between the enamel

and the metal along approximately 70 percent of the interface. The photomicrographs of

pickled and enameled and of vapor deposited chromium and enameled specimens (which did not

spall) showed a black layer along approximately 50 and 20 percent, respectively, of the

interface while the sample of prefired 1100 (which also did not spall) had no black layer

between the metal and the enamel. Thus, there appears to be a "reaction" layer between

the enamel and the metal that may contribute to the enamel's spalling if it constitutes

more than 50 percent of the interfacial area.

Studies of prefired 5086, enameled and fired for ten hours corroborated the existence

of a "reaction" zone (see figure 1), It was also found that the zone contained lead and

Mg2Si particles and a magnesium-rich (brown) zone. Evidently, it was this magnesium rich

zone that we saw earlier as the black layer. When attempts were made to duplicate this

result, it was found that the width of the reaction zone varied considerably. Therefore,

attempts were made to determine the cause of these inconsistent results by examining the

effects of furnace atmosphere on the reaction products. Optical examinations of cross sections of enamels on 1199 + 1% Mg^Si fired in air, oxygen, nitrogen, argon, argon 65% + hydrogen 35%, nitrogen + 30 mm water vapor, nitrogen at .003 mm and flowing oxygen

indicated that the furnace atmosphere had. a very pronounced effect on the reactions that

occurred between the enamel and the metal. The reactions varied from no visible effect

for the enamels fired in air (see figure 2), nitrogen and argon, to a brown magnesium-rich

layer at the interface for the enamels fired in oxygen, and to having globules of lead,

Mg2Si and islands of a magnesium-rich phase present near the interface for enamels fired

in hydrogen, a vacuum nitrogen or an atmosphere containing water vapor. These phases were generally located with the light microscope and identified with the electron

microprobe.

Similar studies of lead-free and silica-free enamels on 1199, 1199 + 1% Mg2Si, and

1199 + 2% Mg indicated that no reaction products were formed on 1199 coated with either

one of the enamels and fired in hydrogen, or coated with the silica-free enamel and fired

in an argon atmosphere. Reaction products were not noted on any of the other specimens

of 1199. Fine spherical particles of metallic cadmium were present throughout the leadfree enamel applied to both Mg2Si- and Mg-containing alloys, except those fired in the

oxygen atmosphere. These magnesium-containing alloys fired in oxygen had a non-continuous,

magnesium-rich phase present adjacent to the interface. The silica-free enamels fired on all these alloys, in all atmospheres except oxygen, produced discreet particles of leadboron phase. Again, these particles were located with the light microscope and

identified with the electron microprobe.

7
3.5 Electron Microscopy

Replica electron microscopy has been used extensively to study the interfacial area

on spalling and non-spalling enamel-metal systems. These studies have shown a very

smooth transition from the enamel to the metal on the non-spalling alloys, but a rough

transition from the enamel to the metal on the alloys that spalled (see figures 3 and 4).

However, this difference was detected only after etching. Studies of the effects of many

different etchants, including antimony trichloride, substantiated the above findings.

The amount of oxide solution (see Section 3.3) was monitored by replica electron

microscopy methods.

Transmission electron microscopy was used on one set of enameled 6061 specimens.

This set of micrographs showed a marked difference in the transition across the interface

on the specimens that spalled and those that did not spall. The interface on the systems

that did not spall appeared smooth from the metal to the enamel with a fairly wide

intermediate zone; on the other hand, the systems that spalled showed a narrow band

that appeared separated from the enamel.

The scanning electron microscope was used to observe the porcelain enamel - metal

interface. These observations substantiated the earlier findings with replica electron

microscopy

.

The scanning electron microscope was also used to examine the fracture-surface after

the enamel was removed by direct-tension pulling. These studies indicated that the

enamel pulled free from the metal only on prefired 5086. The other enamel-metal systems

tested all left a glass-like layer on the enamel surface. This glassy layer appeared

fairly porous for the enamel-metal systems that spalled.

3.6 Electron Microprobe

The electron microprobe was used extensively (see tables 13 and 14) to determine both

the quantitative and qualitative distribution of elements, near the enamel-metal

interface. The two goals of the probe studies were to determine what elements, if any,

accumulate at the interface to cause or cure spalling and to determine if a diffusion

zone existed between the metal and enamel.

The initial probes indicated a build up of magnesium at the interface of the systems

that spalled. However, further studies showed this build up to be erratic and, in

addition, there appeared to be a uniform build up of magnesium on some of the systems

that did not spall. This lead to further investigations to locate .other elements that

might be combining with the magnesium in the alloys where spalling did not occur.

The probe plots in figure 5 indicate the effect of magnesium, sodium, and potassium

on enamel-metal systems that do and do not spall. These data indicate a low background

level of magnesium on the samples that did not spall as opposed to high magnesium

background levels for the systems that did spall. (6061 was the alloy used for these

four samples). Also, the relative concentration of potassium at the interface was greater than the relative concentration of sodium for the systems that did not spall

while the opposite was true for the systems that did spall.

A probe study of pure magnesium that had been prefired, pickled or anodized prior to enameling indicated that the potassium diffused further into the magnesium than the

sodium on the systems that did not spall (anodized and pickled magnesium) while they

diffused about equally into the magnesium on the system that did spall.

A probe study of pickled and prefired 1199 that had been fired for 10 hours indicated

that lead migrated to the interface more readily than potassium on the prefired sample

which spalled. The reverse was true for the pickled sample which did not spall.

8
There was no noticeable diffusion between constituents of the enamel and the metal

when the individual probe traces were observed. However, this data indicated small

differences in the width of the diffusion zone. The overplotted data illustrated in

figure 6 indicates that there is a relatively wide diffusion zone between the porcelain

enamel and the 1100. The diffusion zone for the 6061 is slightly narrower than for the

1100 and probably contains reaction products as indicated by the presence of lead and

magnesium in the diffusion zone between the maximum concentrations of aluminum and

silicon. The diffusion zone in the 5154 alloy apparently contains more reaction products

as indicated by the increased concentration of lead and magnesium. The spall resistance

of these systems follows the same pattern; 1100 has excellent spall resistance, 6061

has intermediate spall resistance and 5154 has poor spall resistance-v Thus, it appears

that the amount of diffusion and reaction products in the diffusion zone affects the

spall resistance of enamel-metal systems.

3.7 X-ray Powder Diffraction

After pickling, 6061 alloy specimens were coated with a clear lead-bearing enamel

and fired for 10 minutes. The enamel was abraded to produce a series of specimens with

decreasing thickness of enamel (approaching the interface) . X-ray powder diffraction

analyses of the remaining enamel revealed increasing amounts of metallic lead as the

interface was approached. Additional studies revealed greater concentrations of lead near the interface when the enamel was applied to a magnesium bearing metal such as 5052

than with the magnesium-silicon alloys such as 6061 and 6063 and essentially no concentration of lead near the interface with the relatively pure alloys such as 1100.

3.8 PEI Adherence Tester

Prior to the initiation of this program. Laboratory G had evaluated the spall

resistance of some enameled aluminum specimens by deforming them as described in ASTM

C-313. These specimens were 3/8 inch thick extrusions with the enamel varied to change

the spall resistance. The appearance of the deformed areas ranged from some fractures

occurring within the glass for systems with good adherence to bright metal for systems

with poor adherence. These results also correlated fairly well with the results of the

antimony trichloride test on these specimens.

3.9 Direct-Tension Pulling Tests

A direct-tension pulling test was investigated as a possible substitute for the spall

test solutions in evaluating the adherence of porcelain enamel on aluminum. The instrument

used was an "Elcometer Adhesion Tester"; this is often referred to as a "button tester".

The test consisted of epoxying a one-inch diameter button on the enamel surface and then

pulling on the button until it was removed along with some enamel.

Preliminary tests on a set of enameled specimens indicated that the appearance of

the "buttonhole" correlated better with spall resistance than did the force required to remove the button (see table 15). The fractures resulting from buttons pulled from 1199 were all in the glass while the fractures occurring on prefired 5086 were at the surface

of the metal. The fractures for pickled 5086 and for both pickled and prefired 6061 were between these two extremes. The visual observations were supported by measurements of the

conductive surface of the buttonholes as described in ASTM C-313. The 1199 has practically

no conductive area while the prefired 5086 has the largest areas. However, the differences

between these extremes are not consistent enough to be the basis of a new test.

These results indicate that, mechanically, the weakest area of the 1199-enamel

system is well into the glass - perhaps at the edge of the relatively wide diffusion

zone between the enamel and the alloy (see section 3.6). The weakest area in the 6061

systems appears closer to the alloy while the 5086 systems often fracture right at the

enamel-metal interface. It is possible that as the magnesium content of the aluminum

is increased, more reaction products are formed in the diffusion zone, making it

mechanically weak.

9
The enamel and metal sides of the tensile fracture on both prefired and pickled

6061 were examined with the electron microprobe attachment on the scanning electron

microscope. This examination revealed that the composition on the enamel side of the

fracture was the same whether the enamel was pulled from the pickled or the prefired

6061. However, the analysis of the metal side of the fracture showed a higher sodium

to potassium ratio for the prefired 6061 than for the pickled 6061. This substantiated

earlier probe findings that there is a greater potassium concentration in the diffusion

zone on pickled and enameled 6061 than on prefired and enameled 6061. This study also

indicated that the enamel-metal system is mechanically weakest on the enamel side of

the diffusion zone.

4. THEORY FOR THE RETENTION OF ADHERENCE OF

PORCELAIN ENAMEL TO ALUMINUM

The data obtained to date suggest that good adherence and good resistance to spalling of porcelain enameled aluminum requires a diffusion of aluminum or aluminum

oxide into the enamel. This diffusion is illustrated by electron microprobe results

(section 3.6) and by partial or complete solution in the enamel of the original oxide

layer on the aluminum (section 3.3). The resulting diffusion zone is not subject to chemical degradation (section 3.5) and is mechanically stronger than the enamel (section

3.9), Magnesium is either absent from the diffusion zone or is associated with enrichments

of alkali metals, particularly potassium (section 3.6).

When spalling occurs, the diffusion zone contains a layer of reaction products. This

diffusion zone may contain magnesium in some form, frequently in large concentrations,

and there is no potassium enrichment associated with the magnesium (section 3.6). Lead

and magnesium silicide have also been observed in the diffusion zone (sections 3.4 and

3.6). This diffusion zone is susceptible to chemical degradation (sections 3.4 and 3.5)

and, in mechanical tests, (sections 3.8 and 3.9), it seems as though it either breaks

itself or it breaks away from the metal surface. The formation of reaction products in

the diffusion zone apparently inhibits the formation of a relatively wide, homogeneous

diffusion zone that is necessary for good adherence. A simplified illustration of the

diffusion zones for systems with good and poor adherence is given in figure 7.

Commercially pure aluminum generally has good adherence and a relatively wide

diffusion zone without a concentration of reaction products. Aluminum-magnesium alloys

with poor spall resistance show a reaction layer in the diffusiofi zone. When chromium,

or its compounds, are present on the surface of the aluminum-magnesium alloys, spalling

is usually diminished but not eliminated. It is assumed that chromium inhibits the

accumulation of reaction products in the diffusion zone. However, the function and

mechanisms for the effect of chromium are not clearly established. Aluminum-magnesiumsilicon alloys may or may not spall depending on the metallurgical state of the alloy

(section 3.1) and the condition of its surface before, enameling (section 3.1 and 3.4).

Here again chromium plays an important role but it is not the only factor.

There appear to be interdependent mechanisms involved when spalling occurs. Apparently the spall solution attacks the aluminum, and possibly the reaction layer, producing a corrosion product and a gas. The corrosion product and gas appear to build up

pressure under the enamel layer which causes the enamel to flake away from the metal.

It could be that a crack is initiated when the spall solution attacks the aluminum at the

interface and this crack propagates more readily in systems where reaction products are present to act as stress concentrators than in systems which do not contain reaction

products.

5. ROUND-ROBIN TESTING OF 6063 ALLOYS

After the theory was suggested, it was decided to see whether the knowledge gained

could be used to predict how to successfully enamel extruded 6063 alloy commercially. This

study included four steps.

10
The first step was the enameling of nine lots of extruded 6101 alloy. This is a closely controlled alloy occurring within the broad range of 6063 compositions. These nine

lots of 6101 were enameled by a commercial firm using their standard pretreatment , enamel

and firing procedures. The enameled specimens all passed the antimony trichloride spall

test. Electron microprobe and optical microscopy failed to show any differences at the

interfacial areas of the specimens, thereby suggesting that differences in spall resistance were minor.

Since the results of the first step were encouraging, it was decided to proceed with

a round-robin test of six 6063 alloys from 3 primary and 2 secondary suppliers. These

specimens were enameled by 5 processors of architectural porcelain enamels on aluminum.

From the results of spall tests on these specimens, it appeared that there must have been

differences in the enamel-pretreatment-firing steps used by the processors to account for

the difference in the spall resistances of the final products. This conclusion was reached

when it was observed that one enameler was able to enamel all 6 lots of 6063 with no spall failures, while the others were only able to enamel 2 or 3 lots of the 6063 without

spall failures (see data in table 16).

Since the second step illustrated that it was possible to successfully enamel 6 different lots of 6063, it was decided to control two of the processing variables in

another round-robin test. In the third step, 4 of the 5 enamelers participating in step

II again enameled the 6 lots of 6063. This time, each enameler applied the same enamel to the 6 lots of 6063 alloys. When these specimens were evaluated after spall

20 hours in the SbCl3 test solution, it wAs found that the spall resistances of samples

produced by 3 of the 4 manufacturers now passed the spall test (see table 16) . In communications with the enamelers, it was found that the enameler whose samples failed the spall

test was the only one who did not use a chrome-containing deoxidizer. Furthermore, of the

3, only one employed it at ambient temperature. In order to confirm the effects of the

deoxidizer, thq fourth step was initiated. In this step, duplicate specimens (12 different

shapes, all 3-ft sections) of 4 lots of aluminum were pretreated in a hot acid-chromecontaining deoxidizer and an ambient temperature chrome-free deoxidizer. The same enamel

was applied to both sets of specimens. They were fired and spall tested. After one cycle

in the antimony trichloride spall test solution, only one lot of aluminum that had been

pretreated" with the ambient temperature, chrome-free deoxidizer failed the test. It was

then decided to extend the spall test by three cycles. At the end of four 20-hour

cycles, in the antimony trichloride spall test solution, gross failures were noted on one additional lot subjected to the ambient temperature, chrome-free deoxidizer while none of

the hot-acid chrome treated specimens failed. It, therefore, seems that 6063 extursions

can be porcelain enameled if care is taken in the selection of the enamel and the pretreatment used.

6. SUMMARY OF FINDINGS AND TECHNIQUES USED IN STUDYING

THE MECHANISMS OF ADHERENCE OF PORCELAIN ENAMEL TO ALUMINUM

A study of the mechanisms of adherence of porcelain enamel to aluminum has been

undertaken during the past seven years. During this study, both commercially available

and specially prepared aluminum alloys and enamels have .been studied with light and electron

microscopy, electron microprobe, and X-ray diffraction. They have been chemically tested

in antimony trichloride and ammonium chloride spall test solutions, and mechanically tested

by deforming and tensile testing. These studies have resulted in a theory for the adherence

of porcelain enamel to aluminum which is that good adherence is the result of the diffusion

of aluminum or aluminum oxide into the enamel without the formation of reaction products in

the diffusion zone.

11
Several findings which relate to enamel-metal systems which spall easily, which do

not spall, and findings which relate to all systems are given below:

Summary of findings relating to easily spalled systems

A. The interface is mechanically weak

1. Enamel is readily removed by direct-tension pulling

2. Enamel is readily removed by deforming

B. Etching solutions preferentially attack the interface of

cross-section

1. In major cases, this can be observed with the light microscope

2. This can always be observed at high magnification with

electron microscopes

C. Large concentrations of magnesium are sometimes found close to the enamelmetal-interface

D. The oxide layer is not reduced in thickness

E. The oxide layer is rich in magnesium

F. Flakes of enamel fracture off with force in spall solutions

G. Reaction products containing lead and magnesium are often found in the

diffusion zone.

Summary of findings relating to non-spalling systems

A. The interface is strong'

1. Direct tension pulling tests fracture the system in the porcelain enamel

2. Deformation tests fracture the system in the porcelain enamel

B. Etching solutions do not show preferential attack at the interface

C. Magnesium concentrations at the interface are associated with concentrations

of alkali metals or are non-existent

D. A relatively wide diffusion zone exists

E. The oxide layer is reduced in thickness

F. Potassium diffusion results in enrichments of potassium at or near the

interface.

12
Summary of findings relating to all systems

A. Elements in the metal other than magnesium are not diffused to the surface

B. Various humidity exposures, accelerated weathering tests, etc., have not

produced accelerated spall failures which could be duplicated

C. Elements dissolved by the spall test solution reflect the composition of the

alloy being tested rather than the composition of the enamel at the interface

D. Moisture in the furnace atmosphere does not affect the spall resistance of a given enamel-metal system.

7 . ACKNOWLEDGMENT

This report would not be complete without acknowledging those companies that contributed

to this project. The Ferro Corporation (the frit company) should be acknowledged for

donating the full-time services of a research associate on this project for three and a half

years, for preparing the enameled samples and providing additional technical guidance

concerning the porcelain enamel composition and properties. The four aluminum companies

participating in this project, the Aluminum Company of America, The Aluminum Company of

Canada, The Reynold's Metals Company and the Kaiser Metal and Chemical Company, should also

be acknowledged for contributing technical guidance regarding the metallurgy of aluminum

and for performing many of the laboratory analyses reported herein. These five companies,

together with the remaining member companies of the Aluminum Council, should also be

acknowledged for their financial assistance which made this project possible.

13
8. BIBLIOGRAPHY OF PREVIOUS REPORTS OF THIS STUDY

A. Published Reports

1. Gugeler, A, L. and Ballard, D. B. , "The Aluminum-Porcelain Enamel Interface as Observed by Electron Microscopy", Bull. Am. Cer. Soc. 48 (8), 842 (1969).

2. Gugeler, A. L. , "A Study of the Adherence of Porcelain Enamel to Aluminum",

Proceedings of the PEI Technical Forum, 29 (292) 1967, Porcelain Enamel Institute,

1900 L Street, N.W. , Washington, D. C. 20036.

3. Gugeler, A. L. , "A Study of the Adherence of Porcelain Enamel to Aluminum",

Proceedings of the PEI Technical Forum, 31 (37) 1969.

4. Baker, M. A. , "Study of the Adherence of Porcelain Enamel to Aluminum-Use of

Electron Microscope and Electron Microprobe", Proceedings of the PEI Technical

Forum 32 (48) 1970.

B. Unpublished Reports

1. Gugeler, A. L. , "Progress Report, August 1, 1966 - April 30, 1967", nbS

Report 9533.

2. Gugeler, A. L. , "Progress Report, May 1, 1967 - July 31, 1969", NBS Report 9901.

3. Gugeler, A. L. , "Progress Report, August 1, 1968 - Jan. 31, 1969",

NBS Report 10012.

4. Gugeler, A. L. , "Progress Report, Feb. 1, 1969 - June 30, 1969", NBS Report 10050.

5. Baker M. A., "Summary Report of the Technical Advisory Committee, Study of the

Adherence of Porcelain Enamel on Aluminum, August 1, 1966 - July 30, 1970",

NBS Report 10346.

6. Proceedings of the Porcelain Enamel Institute Technical Advisory Committee

Seminar, Aluminum Council 1970.

Although these are unpublished reports to the sponsor, they are available through

the sponsor, the Porcelain Enamel Institute, 1900 L Street, N. W. , Washington, D. C. 20036.

14
oo

60 odotHooooo I I I I I I I I I I' ( I I I o O rHO

COOo oooo 1 11 1 1 1 1 1 1 t o o CM o 1 1 1 1 u 1 1 1 1 1 O o o o o

<-\ o in 1 r o u-l .-1 o rH 00

u c 1 1 o o ! O o o o O C s 1 1 1 (U 1 1 o o 1 O o o O O o au

0)a o 1 1 CM 1 1 CN

CO c 1 1 o o 1 OO o O o u 1 1 1 1 O c 1 1 o o 1 o 1 a d O d

(U3

4J •H

•P iHH o

to o O o <-{ o cn COO CM

C <u o O o in <!• CM

O o iH CM ou o O o o o O o O o O o wc

•Ho <! o

iHO o o o- -vTO o

^^ •HO <r o t-l

m <^ o O .-1 <: O o o o O o o o o o O O CM o < 1 O in CM tH CM VO 1 CN O 1 O iH iH CN O O o 1 o >^ 1 1 u u d 1 C o O O O o o 1 d o o u u

tau

u o o 1 (>J 1 in 00 a\ ni 1 vO 00 1 i 00 in CM in CO 11 d iH 11 1 o o o o CO CO >> >^

X> x> Xl •X) (U (U •H •H

CMm o tH iH

iH in CO CN CO 00 D. <x a\ a^ tH tH tH in r- <r O as tH P- {X3

0^ 00 00 CJ> 00 ON as in

m to

M

0^ CT^ as o> as 6 s 3 3 C C

•H •Hs

tH CN 3

•H iH iH \ < <: a\ CTi CN CJ^ CO r~ -vT ON 60 <J\ 60 o o in in in CO

rH .HS iH tH iH o O CN vO iH o

iH iH tH tH iH vO in

m in in ^1

•T30)

CO>.

iHC

•H

0)

60OU

Q.

(U

T3

(-1 ou

60

to T)

>^

O

M n)

nj tH > o.

0)u

w 0

•H 3

to

C

O -H

(X E O iH

COo&oo

MS

(UN

>^ iH

COoc

0)u

(U I

CO

0)c

60

Cfl B

4-1 •H

)-( 3

O- J3

60

•H

T3C

cfl

COOO

CO

CO>^O

0) H

15
Table 2. Oxide Composition of the Basic Tan Enamel, Including

Both the Frit and Mill Additions.

Oxide Weight Percent

PbO 26.47

TiO^ 24.85

Si02 22.38

Na20 10.46

3.67

BaO 3.22

Sb20^ 2.33

Li20 1.67

B2O3 1.41

Cr^O^ 1.28

ZnO 0.99

Fe203 0.96

AI2O3 0.32

16
Table 3. Oxide Compositions of the Frits Used in the Lead-Free,

Silica-Free and Basic White Lead-Silicate Enamels.

Oxide Weight percent in frits for:

Basic White Lead- Lead-Free Silica-Free

Silicate Enamel Enamel Enamel

PbO 33 0. 05 high

TiO^ 14 18 high

Si02 30 30 0. 05

T Q 10 low or absent

2 10 n.d.

BaO 4 0. 03 0. 0 Sb20^ J

A A 0.0

Li20 L . 0 3.5 0

1.0 5 high

U. UUUD U . UUUD U . UU

"ZnO 0.0 2 high

^^2°3 0.1 0. 05 0. 05

AI2O3

MgO 0.05

P2O5 n.d. 2.5 n.d.

CaO 0.1 0.1 0.01

Mn02 0.0003 0.0005 0.00

CuO 0.003 0.003 0.00

SrO 0.1 1.5 0.00

Zr02 0.0 0.05 present

Nb205 0.0 0.0 0.03

Cd02 0.03 5 0.0

SnO, 0.001 0.001 0.0

17
Table 4. Summary of Spall Test Results for Various Alloys

Alloy Pretreatment Spall Test Results

1199 Prefire Pass

1199 Pickle Pass

1100 Prefire Piss

1100 Pickle Pass

6061 Prefire Fail

6061 Pickle Pass

5086 Prefire Fail

5086 Pickle Fail

5154 Prefire Fail

5154 Pickle Fail

5257 Prefire Pass

18
Table 5. Spall Resistance of Magnesium

Pretreatment Spall Test Results

Prefire Fall

Pickled Pass

Vapor deposited chromium Not Tested*

Anodized, unsealed Not Tested**

Anodized plus vapor deposited chromium Not Tested**

Anodized, water sealed Not Tested**

Anodized plus sodiuni dichromate sealed Pass

* The enamel did not wet the metal so the specimen was not spall

tested

.

** The enamel spalled immediately after firing, no spall test was

needed.

19
vO

(U

03 cn 1—1 H

o^

w CO cn 03 -H nj 03 03 in &.

0) T-l CM CM Cm CN CO

4-J n)O

•H iH r-H i-i iH

i-l 0^ !H iH .H

•H OS 00 cfl ca 6^ 03 ^s 03 rH <N in ft o O ft o fX 1 C iH r~ CO CM CO m CO CN CO T3 O

030)

M

I-l r-f iH I-l 0) •H iH iH 5^5 -H rH

0) e 0^ 6-S CO cfl 03O 03 s-s 03 iJ rH i-H 1 o P< o O a Oh •H C 60 CO iH C« CT> CO w S u 1—1 1—1

i-H I—1

•H 1-1

H iH iH iH

cn 03 03 03 ccS nj o O O. O o a

P3 CO CO iH CO 00 CO

(U H

00

C

4JC

0)au

CO

0)

I-l

(Uu

<4H C^ o rH

rH

Hi cn 0) o M 0)e cn 1 rH 0^

C3 o Q) OS o d) g iH CN

•H rH rH CO c

•H

W

CO Q)

0) (1) cn J.) O

rH XI

0) a) rH rH u g 1 rH

pn 03 03 1 Q CJ 13 w •rl 03 rH

(U a) cn •H rH

4J

u 60 \o

03 rHO

C o 3 o •H cn rH cu cn •H oi

4J CO iH 1 4-1 3 •C3 cn

cn 03 (U cu (U H C3^ Pi rH rH rH

4-1 <U rH

cn 4-1 03

(1) •H cx o H CO

cn tJ^ rH rH CJ^ rH O rH CN

03 •H rH

a, cn CO 03 pq

w o 0)

<u ^s

!-i rH rH

li^ rH 1 i

T3

03

(1) CO rJ rHVOO

oc

^S rH O 03 o n. rH CO

6-S rH O 03 o &, rH CO

rH

O OJ o o. rH CO ^ rH O 0) o &, rH CO

cn

tn

03 Ph

cn

cn

03

CO

cn

03

03

O CL, <f CO

T3

0) rH

.iio

•H

rH

O 03 o a. rH C/3

6^ rH O 03(X rH CO

5^ rH O 03 o eu iH CA)

rH

O 03 O CI,

cn

tn

03 CM

cn

cnOS eu

•a

cuu

•HUh

(U

>-< CM

6^ rH O 03 rH CO

rH o 0) o a- rH CO

6^ rH O 03 O Pu rH CO

S-S rH O 03P03 03 in CX O O,

CO rH C(5

e-s 03 O Cu in c/3

cn

cn

03 CMoo

-a

cu rHo

•HCM20

rH

O Cfl o a. rH CO

S-S rH o OS O Cu rH CAl

5^ rH O 03p. rH CO

rH o cd O Pi, rH CO

S-S 03 in G.

CO

03 0 IX 01 CO

cncn

OS

03 CO B< ccS

O CU

O CXO CX ro CO CO cA) c/:i O

cu CM

14-1 oc

<u

4-1

cu

cu

4-1

cn

(U

4-1

Cfl o

•HT3C

•Hc

cu>

0)00

CO 4Jc

0)aM

0)&.

(U

cu

13

0) rH

•H

03 iw

0)Cu

03

CD03 •O

CU

4-1 cn • •H nJ rH cutM

CO 03 rH

(U'ld E dJ

C3 rH C rH

CU 03Cu

0) cn

cno a)
CO e Q) O XIU

n)

C

0) -H u ^<

-a c

iH -H

q)O

CL, (U to P<

14-1 O

60

O

(U

C iw

B (U (U u kJ O Qm

0) P

•X rH CO

0) 0) T3

•o

B (U

C •H S

J3

u

u

0) o

-a

M 0) Q

rt •a g u *j

nj s CO H c (1) H c 1 .H O iH

<! n)

CO P- CO

0) iH IM

CO 0)

O -U

to Pi ^ .H c

4J

w CO

CO P(S (U c H

rt iH rH

rH 0) t>0

tfl

a

a

u •H

B

CO o >j 0) o

P4 •H

H o o §

(0 c

•H

a (u • 1

•H

B c u •H H B 1

0)p.

4-1 CO

(U

!-l 4J

0)

VIO

O I O I

csi

m 00 00 OS

rH CN i-H iH iH CN

in en ON -;)• ON u-1 <r -d- CO <) ro <»•

in lo in in <r<NiniH<Nvoor^ooooiH vo <r cN in ro r~

.H iH iH iH iH iH

C -U to

OJ OJ 01 ^ ^ 4J

0) .H O r-l • C to <U to O- O 4-1 C to

toM

4J CO (U

CO 0) 4J H M m

CO to

eu iH M >H -a

to <u iH a. to iH to o

to p- a. c >< to -H (L)

4J (U iH

to

O tO

)-i

C 4-1

O (U 01 » u B ^ M-l H

4J -H to

CO

0) CD 14-1 4-1 iH O

to ,P a CO -u •H <U Cl T3 O 3 C -H O

•H 4JB

O c3 C

rH CD o

<4-4 Ci -U O

COCO o d

to eu n (U 4-1 to

to 0)

B

•H

4-) 4-1 in in in in in in eu CO o eu ro fn fo en n CJN ON (3N CJN tTN CM vl- in VO c CO rH rH rH rH iH rH to rH

4J cu CO

to

B 3

•H •H CO CO o •H

cu cu >

V4

a o o o o o o O o O O O o o o o o o CO to o o o o o o O o -a- o o o rH o o o o ON o o tJN 0\ o 0\ o tTN o ON o o rH tu c

tH rH jH iH rH rH rH rH rH rH rH to

u o

4-> 4-1 p- o

to CO to

B xl

(1) (U tu

4-1

u CO

to o to iH rH <u rP H o O o o o o o o o O O rH o o o o o o rO o

CO rH

O tH iH iH o rH rH rH rH rH to o rH o rH rH o to P- \0 vO p- vO vO vO <u 4J W to

4-1 o

(U (U

u

J! to c

4J 4J tu c to 4J <u 00 ilO CO > c c o •H eu •H T3 t3 •H XJ T3 •H 60

CD 0) -o xs -a -a T3 (U cu <U 'O rH tu cu T) Xl cu cu CO M Q) 0) cu <u tu (U U ^4 U CU •H 1-4 u (U (U u )-4 c CO

to •H iH iH tH rH rH •H •H •H rH CO •H •H rH rH •H •H •H •H CU 14-1 ^ ^ ^ UH 14H MH A! t4H 14H <4H 14H 14H fU u a o o o <U CU cu a cu (U o o cu cu (U to

CO •H •H •H •rl •H

M

uu •H CO V4 •H

u ^4 c c c c PL, PL, Pl4 PU P4 PM tu fu PLl PM PL4 Pik PM P4 o to eu

cu 1 14H •H o 0) CJ U u B eu (U cu ri<! to p. a c CO to

1/1 CO CO CJS iH tjs ON rH vO ON rH rH vD CJN VD VD rH vO rH cu (U a\ ON vO o\ \0 00 ON VO VO 00 C3\ 00 00 VO 00 VO x: X! —

iH iH

O iH rHOO rHO o O ^—s

rH o o o o o <: 4-) 4J

to iH .H SO iH VO in rH vO VO in rP rH in in vO in vD *

21
• * c

•H

En

•H

>-i 00o

in

OOO

Q)00 o

cd U

(1) o o u o

0) Cm

C3o cy "H

•H

J-< C30 1—i O o o 1—1

in

rC

CJ

l-J •H

CO J-( i-H Q) H H O

>^ 1—1 C

1—t o

n) "6 cx H o 4-1 o

I-H

14-1 < 1—1 o co

CO •H

4-) CO>> t-H I—1 O

(/) c CD •a \o

CO •iH 00

<u o > H o in

•H

4-1 .H

Cfl i-H

u iH

4J CO •H a s O

iH (/I 3

CO •H c C

o- •H

Oo

>, o u rH

•H

>> 4Jc

CO CO3

CD-

)-i (U vO

4-1 00

00 CO

O

in

<u rH rH

0) \D

CO iH o H >H vO

•H

4-1 o

CO o

•H rH n rH

4-1 s§M

CO 4J

<U Sc

cu6

COcw

0)o

PQc

•H

00

CJ •H3OOO

in ro 00

O rH rH 00 in in C3^ m CN OS ro 00 c^^ O rH O <>J <f O

C~-l CM

00 CNO rH rH rH O CM rH O O

CT\ o o o o o

CJS

r-^

m o <f vo

in rH ^ m o o

C3^O

OOOO

OS

in rH rH CM rH CM

rH in in rH o o o o o o o

CTi I I I I

CNJ OS rH rH O 00 o o O <n o O

vf in

CM 00

U-l 13 0) T3O CJ

14H cu Id

X

a

T3 CO COO

O I

-O XI rQ

U ^ I u r I CO I I

rH

w IH ,43 -a 13

a ^ 0) -a u

14-1 ,43 I ,0 IN- ^ B e 6 3 D 3 P 3 •H C •H o •H U CO •H E o c cu § O C •H CO O C M o iH 4J a oo J= •H •H o CO U M CO H M u s ^ Q)

O ,43

a 0) o 43

CO l4HOCUO,J3,43 S 00,43J3

CUaCo

CO TD CO I 00c

•H

V4M3 CO -a CO I ooo

CO CO I I a -a -a o

TJO CO CO

CU

CO

CUC rH

CO <U 00 ^ C O

CO -H S g Z

CUa

n) w

CU

so <f 00 rH

O o CM in m

CM <d- -d- <s-i rH CO O sa CM

rH CM I I I I I I I I I I I I I I I I I I I I U -O ID (U t3 a t3 13 (U T3

,43 e^.U

a 13

aH

>. rHco

00 CO CO CO -a I c

•H

1-1 3

CJ CO CO c^-O I OO

CO 4JC CO CO I o. I CU

(U c. T3 <U CU

Q) CU <U ,Q

CU 13 ,43 c-. ,43 B a § 0 3 3 e O -rH -H 13 -H

1-1 l-l T3 CO 4-1 O CO O <U C m m cyD <;

CU a

CU

4-1 Oc

0)

0) 4J

1-1 CU x:c

•HH

1-1 M3

CJuo

CO CO ,43

C^- CO ,43

,43 CO CO

CO CO cO

c- CO I I CO c^.

CO CO ^

,43 13 CJ

,43 XI 43a3 e -H M 3 4-1 <U -H C > O O

iH rH

M

•H CO 4J CO U CO

CO CD CO pj

22
60 U

COc

Q)B

•HO

(U

<ucw

Si e o u H

4-1 60 o g o u

4-1 60 O S HI C C O

CD -H a -u C tfl o ^ U 4-1

tfl 4-1 o o H ^—s

rHiH

tfl tfl 4-1 ft

(U CO ^—' S 6

tfl 4-1 601 60

to tu

<*—s

.H

a

M iH .H

03 tfl tfl tfl .§

pq 4J {X

(U to

a 6^

(UfX '-^ CO tfl 4-1 60 o U e

cu

H

rH

0) al

y—V

4-1 60 c O s w H ^

o

CO 00 r~~

OO 1-1 o o o o o o o o o O CN VD O CTi o o o o o o o o o o

vo vO

O C>J o o o o o o o o o o O tN o o o O O O iH o o o o o * -K -K * *

<r iH CM

iH tH iH

OO

C c o O O O O O O -rl •H 4-1

4-1 3 3 O O O u~i i-l iH O O O O iH O O CO

CO o o o o o 4J

4-1 CO

CO (U

tu

H

H

O CN

OO v£>

O iH >HO iH

.H .H

iH

O

OOOO tfl tfl P,

CX CO

CO o o in <t iH o o v£) a\ <yi 0)

!-i X)

0)OOOO iH -H III )-l

tfl o

Id o <f

O o <!• vO tN

iH o o o O

O o O

O iH

•H •H

4-1 CD <D o CD

O c o o O CD

O

CO o

•Hn o o <t <f o o 00 CN <(• o o O o u~l CT\ o o O O o o o CN iH

•it *3C

O iH t-lO

O

O ^ si- iH tN O 1-1 rH O iH O O O O O O O o m o o o o o o o o o o X O n iH rH O O ^ 00

r-l o o o o

i-H \0 vO in ^ m ro CN o o o o in o o o o o O O rH O- VD o o in CO CJN O O O O CO

<N CO <f

O

O

OO rHO o o o o o O O 00 VO O rH CN O O O rH O

(N <r rH oCsl

t30

m vo

C o rH o o in o

-H

O

O

OO

O 4-1 3

rH o o cy\ o o o o o m o CN CO O O O CN 4J

to

cu H

vO rH rH <)• t3^ rH O O O O O rH

cfl

O

O

OOO ft I I CO O O ^ rn CN cu O O CO rH 00 X)H o o o o m i-l I o

rH

x;

CJ •H

^4 HcoB

•H

4-1 o n rH <N o

CN rH in CN rH

rH

O

OO CN o o o o o O O <r 0^ VO

to

OOO CN

O CO rH rH vO O vO vO 00

rHO

O

O

rH CO vo vo in o to

vo rH O rH I I m

m Ov CO

rHOI I

vD in o o

tN Cvl I I o o

r~- CO O rH o

rH VD

O CM o o<r •<( in CO o o tN <r

VH

rHvo 00 • c

in -HM3

Xl

X) vO 4-1 rH to • cu rH U

CO

tu rH

ftI

CO

(U

CO

O r-. rH rH o o

vD r~ o o o in

vO

in CJ^ rH CN o O -H o ^

CO r~- <f rH

OOO <N co

COc

•H

ft in >> • XI vo

rH 13

(U

CJ^ CO o o

in in

CO

O o o o o o o o O CN O O O csl 00

00 <r o 00 O rH CO CO CN o o o o o O sT O VD CN O 00 ^ rH o o rH m t?> o m in o o

00 CO o

vD r~- in CTi to

rH rH VC CN CO o o o o o O -* in CO rH O CM in 00 O O CN <N r~ O to rH rH vo O O VD vO 00

rH

OO

OO

rH to vo vo in
< u

>,

^1

0) o

>>

u

ca

1-1 ^-1 o

0) XI

T3 n) •Ho

XI

<u

l-J 03 •H 6

U-i o

QJ ^-l U •u

PL, 0360

M-l

C

m

O <;

03

03 o

0) 4J g

nj

O o

•H

-CH

CO 4J

0}u

60

03

C

nj •H >^

0) S-i

O 3

CO

O 03 n) 03 O e

0) o o o g

!-i A! tS O iH 03 •H .H 00 rC n) C H (-1 <: 3

0) 4-1 T3 n) •H

!«: o <+-! PQ O

>,

03 (U 1-1

d 03 TJ o

iH •H 4-) X Cfl 0) O ;j iH o o

•H Xi

(0 CO H H

4-1 c

M) cou O

iHrH

<: o o -* CSl iH

CN 00 in in ro

,H

O o OOO

CN CM

CSJ vO < sj- O ro O cn cn 0^ a^ CN iH

r-( CO <r CN 00 o vO o o <f

ro CN rH CN

r-H CSJ CNl r—i CN

in c^ 1 00 in in 1 CD o o ro o iH en -a- o VO in in

<-\

O o <-{ iH vO in m

24
toococ

•H

i-1 3aoo

COu

cd hJ

(U Xl

•HXo

cu

•H

CO

(UC

60

CS

cfl H

CO <u

0)

u

C (X 60

CO 13 S C

CO c

•H >^

Q) iH U CO c

<U 3

^1 4-i CU CO

14-1 •H 14-1 o o

1) 4J

>-i c

•H Q)

a) !-l

s-i CU

Pl, CL, C '

•H

U

(U 6 >^ 3 CO •H

to

CU CU C T3

00 -H

CO

X S O

<U>^

CO

•a

•Ho

60c

•H I

>J3ooOc

CU 60 -MOu o

vD

00 oI o o o o m <r as o o o o o O o ro 00 1 o CX) vO 11 c rH o o iH

CSl o 00 iH o o o c^ CO o o o o o r-1 o O o

CM o o o o o iH CO O o o o O o m <r 1 1 00 uO r~ ^r^ 11 11 o <~> o en O rH ro -a- O vD VD u-1 LT) iH O o vO rH

rH VO vOm

25
Table 12. Summary of Oxide Solution Measurements on Anodized Aluminum and Magnesium

Specimen Thickness of Anodized Layer Change in

Before After Anodized

Enameling Enameling Layer

Angstroms Angstroms Angstroms

Aluminum Anodized in Sulfuric Acid

1199 3,000

1199 26,000

1199 Alkali Chrome 9,000

1199 Alumina-rich 28,000

Enamel

3003 15,000

5053 2,000

5053 20,000

5086 (Alcoa 100)* 25,000

Unsealed

5086 (NaOH)* Dichromate 26,000

Sealed

5086 (NaOH)* Vapor Chrome 28,000

0,000

21,000

4,000

23,000

16,000

3,000

22,000

27,000

28,000

29,000

Magnesium Anodized in Sodium Hydroxide

Dichromate Sealed 15,000 13,000

-3,000

-5,000

-5,000

-5,000

1,000

1,000

2,000

2,000

2,000

1,000

-2,000

*Pre-anodizing treatment.

26
I pdww www WW W CJO WM Q eQpQpqpqpqrtpqpqpQcq

w

to X X X X X X

•HH

X X !x!

3

XXX X X X X

to s XXX XXX X X X XX X xxxxxxxxxx

•H XXX

XXX X X

60 ^

•H a c U -H -H

•H H B w ^ ooo ooo oo o oo oo o oooooooooo iHiHiH iHiHiH 1-liH i-H rHiH iHr-l rH l-I^OO^OOlHOOOO ro ro v£) c*^ CO

c c pi c c c c

<u cfl CO CO CO CO to 0 <U 0) (U (U CU (U 4J rH iH rH rH rH

cfl O U U u u u tu <u

(U u IH u 0) 0) OJ Q) 0) 0) 0) <u 0) •H •H •H rH rH rH rH rH rH rH rH rH rH s 0 a a m MH m ^

a> <U (U J(U (U (U o O O o o o O o o o

J3 ^1 ^4 u •H •H •H •H •H •H •H •H •H •H

Ph u O u U PL( CM PM PM PM PU PM PlH PL( Ph Pi

OrH^ -*rHr^ <!• -*rH -*rH VD ,-{<-t<-{r-t^r-^^rA\D^ OvOlO l/SvDiri OiO lOvD lOvO tX5 vOvOvOvOOOvOvOvOOOtJO rHOrH rHOvO rHrH rH rHO rHO O OOOOOOOOOO rH*Oin ITi^LTi rHin lO lOvD LTivO vDvDvDvOlOvOvDvOLTlin

27
as < < < QQQQQ QQQ Q

IdI

•HP

c

O

u

H

00

•H e c

(-1 -H -H

•H H e

X XX

X X X X X XXX

X X X X X

X ^ ^ ^

^ X X X

o

X ^ X

X XX

X XX

o o o

X X X X X X XXX

o o XXX X o o

oooooo ooo o

iHiHOOiHrH iHOO O

(Us

(UM

(1< •H

T3 T3 13 o T3 T3 X) -a

OJ 0) e -a 0) (1) CU 0) T) (U

i-l 0) N o T) (U 0) U CU u

•H iH •H u •H •H r-l •H •H •H -H •H

M-l AS ^ M-f ^ 14-1 U-l U-l <D O o o cfl o <1) O a) o a) 0) 0) a

•H c •H (U •H >-< •H •H ^1 •H ^

Pi (l4 <: P Ph Ph PL. Cl, PM P-(

o O

PM Ph PM

. 00 . 60 • Ml W a S ffi S

O '^O ^ OOOOOO \0 vO "^O ^ O

0> 0^ a^

cr» CTt CT> 00o

28
QOQQQQOOQQQPQPQO ppmpqpqpqpcpq pq

to (U (U

CO

*>v

cd u

J-I

niP

r~i H

Oh rs O

rHw Ph

c o

4Jo

GJ

.

*H

4J

cfl 4Jc

d

o*

WD •H :^ 13

a; •HTJ

13

4-1 •H C

•H

•H H s W •—

c

CU§

•U w c

(UB

4-1

ct) iH OJ

0) u

.H OJ H

X X

X X

X X

X X

X X

X

X X

X X

X X

X X

X X

xxxxxxxx

xxxxxxxxxxxx

XX XXX X. xxxxxxxx

oooooooooooooooo OOOOtH(r)cy\O.Hroa\OiHrOcriO

v£3 o ro ro n

XXXXXXXX

OOOOOOOO l^fOO^Ol-^MO^O

fO CO

0) OJ 0) 01 OJ OJ 0) u ^J OJ OJ Q) CU (U (U (U U !-( u 0) <u tu <U 0) CU CU tu a) CU OJ •H •H •H iH pH iH H rH •H •H •H •H t-i iH rH rH iH iH rH rH rH rH

M-l M-J A! ^ ^ ^ ^ in 4-1 A! A! ^ AS Ai a: Ai Ai A!

CU Q) (U a a O CJ O O U Q) a) 0) CU o o O o a O O O o o o a u !-i •H •H •H H •H •H •H yi (-( •H •H •H •H •H •H •H •H •H •H •H •H

CM PM PM PM Ph p-i PL. PL, PM PM CU PM Ph PM Ph Ph Ph PM PM PM

o CXDOO^OvDOOCOCOOOOOCOOOOOvD'.DvDO OrH OOOOOOOOOOOOOOOO mio^^OLTiuriLriiriinLnLninvo^DOvo

rHrHrHrHvOvDvOvO

v£)vDvOvOC»00 00CX3 OOOOOOOO

29
m pq pq pq a Q a a

0) I4-1

X X !»! I«! X X X X XXX X X X X X X

60C 0) • •H 6 C

•H H e

fn ^

O O O O

iH ro a^ O O O OiH ON iH a^ O

ON

Id

0)N

•HX)

•HX

O

OJ Q

-a

•HX

O

(1) Q

O O

ON ON o o o --^ iH O O

o o

o o

ON ON o o o o ^ rH iH O O

o o

o

oNO

0) 0) Qi Q) 0) 0) OJ cu 0) 0) <U (U 0) <U (U (1) (U

(U ;j u u <U OJ )-j M )-i H (U !-i M (U (U !-4 0) !^ ^1 0)

^1 •H •H •H •H iH •H •rl •H •H •H •H •H •H •H iH •H r-H •H rH -H •W iH •H

•u y-i M-l 14-1 M-l M-l M-l y-i M-l 14-1 A! 4-1 ^ U-l M-l ^ M-l OJ CD (U 0) Q) O O (U 0) 0) OJ CD <U (U u di y Q) O 0) O 0) O (U O 0) M U !-< •H H U M )-l I-J (M •H U •H U •H !-i •H U •H •H V4 Ph CU PM PL. PM PM PM Pm PM PM PM PM PM PM Ph Ph Ph P4 P4 PM Ph PM

o nD NO nD

00 00 00 00 o o o o in in Lo LTi

vO vO >sO vXJ o o o o

NO ND nD NO

NOo

NO

NOo

NO

NO nD nO nO no O O O O O

vD \0 vO

\Q vO vD o o o o o o

NO NO NO NO NO NO

NO NO o o

NO NO

NO

00oin

30
VD o-)

O

m rH

O o oa

Cfl in CM \0 rH §oau

(U

<uoao

(U

<!

O o o 3

CO

Qi

4-1 CO

0) H

00 HiH3

PM

O. •H

COcH

4-1 O

(U •HQ

O

>^

00

4J ^ 9 C 3

PhO

4J 13

<U

>-i •H

,s

lU

CJMO

1^

U

to3 , o<cog

0)o.

CO 13co

p. <^ oo oo o O

O

O o CM <! o o o

CO

O

<f CO o o o

\o <r o n ^ -sT o o O O O O

CO CO CO CO CO CO

u

60

•H

B3 o •H H

OOoo ooo ooo o o

bO rH C (U

•"-I 6 o O

<U

U -H •H o O

H •H

H e vO

,Q

CO H

4JC

0)S

4-1 CO

(U

>-l 4J

0)

•a T3

-a cu (U

0)u (Uu (U

U

rH •H rH •H rH •rl ^ 14H A! HH o o 0) o (U •H )-l •H •H

PL,

31
Table 16. Spall Test Results from the First and Second

Round-Robin Tests on 6063 Aluminum Alloys

Alloy

No. First Round-Robin

Enameler

C D

Second Round-Robin

Enameler

C D

Pass

Pass

Pass

Pass

Pass

Fail

Fail

Fail

Fail

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Fail

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Fail

Fail

Fail

Fail

Fail

Fail

Pass

Pass

Fail

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Fail

Fail

Fail

Pass

Pass

Fail

Pass

Fail

Fail

Pass Fail Pass Pass

Pass

Pass

Pass

Pass

Pass

Fail

Pass

Pass

Pass

Pass

Pass

Fail

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Fail

Fall

Pass

Pass

Pass

Pass

Pass

Pass

Fail

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

32
Normal enamel structure showing

glass grains and TiO precipitate

Reaction Zone - Pb particles

Mg2Si particles

Mg rich zone Mg Depleted Zone , Mg - 1.6%, No Mg^Si

Grey Al-Fe(Mn)Si phase

Normal 5086 Structure

Mg - 3.0%

Mg^Si particles ( Not distinguishable

Al-Fe(Mn)Si phase in black and

white photograph.)

Al - aluminum matrix

500X

FIGURE 1 METALLOGRAPHIC CROSS SECTION OF ENAMELED AND

SIXTEEN HOUR FIRED 5086 ALLOY SHOWING REACTION ZONE

Normal enamel structure showing glass

grains and Ti02 precipitate

Normal 1199 + 1% Mg Si structure

FIGURE 2 METALLOGRAPHIC CROSS SECTION OF ENAMELED AND FIFTEEN HOUR

FIRED SUPER PURITY ALUMINUM WITH 1% Mg SI. ILLUSTRATING

THE ABSENCE OF ANY REACTION PRODUCTS. (500X)

33
Metal Enamel

FIGURE 3 PHOTOMICROGRAPH OF REPLICA OF POLISHED CROSS SECTION OF

ENAMELED 13D0 (GOOD ADHERENCE) ETCHED WITH

5% NaOH (8000 MAGNIFICATION)

Metal Enamel

FIGURE A PHOTOMICROGRAPH OF REPLICA OF POLISHED CROSS SECTION OF

ENAMELED 5154 (POOR ADHERENCE) ETCHED WITH

5% NaOH (8000 MAGNIFICATION)

34
ENAMEL ALUMINUM ENAMEL ALUMINUM

A A :«t

f V /

\

• • •

j Na Ia

U/ V

I

• •

i 1 A

/ 'J' DISTANCE

Prefired 6061, 10 min. at 1000°,

Borderline Spall.

Pickled 6061, 10 min. at 1000°, No

Spall.

DISTANCE

Prefired 6061, 10 hr. at 1000°,

Spalled.

Pickled 6061, 10 hr. at 1000°, No

Spall.

Figure 5. Microprobe traces for Sodium, Potassium, Magnesium and Chromium

on 6061 with various pretreatments and firing condition.

35
ENAMEL METAL

Prefired 515A, Spalled.

Figure 6. Microprobe Traces for Silicon, Lead, Aluminum and Magnesium

on 1100, 6061, and 5154.

36
SYSTEM WITH NO SPALLING

t

!2O

H

W

U

o

ENAMEL ALUMINUM

L DIFFUSION

ZONE

DISTANCE

SYSTEM OTIH SEVERE SPALLING

DISTANCE »

Figure 7. Schematic drawing of microprobe traces showing the concentration

of a reaction product in the diffusion zone.

37
NBS-114A (REV. 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHFET

1. PUBLICATION OR REPORT NO. NBS BSS-.SQ

2. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

The Adherence of Porcelain Enamel to Aluminum

5. Publication Date

6. Performing Organization Code

7. AUTHOR(S)

Margaret A, Baker

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS ' DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No. 4A1 71

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Porcelain Enamel Institute

1900 L Street, NW

Washington, DC 20036

13. Type of Report & Period Covered Final Report

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

Library of Congress Catalog Card Number: 74-23734

16. ABSTRACT (A 200-word or less [actual summary ol most significant information. If document includes a significant

bibliography or literature survey, mention it here.) Light and electron microscopy, electron microprobe, and X-ray diffraction

techniques were used to determine the mechanisms of adherence of porcelain

enamel to alumintim. A theory is presented that adherence depends upon diffusion

of aluminum into the enamel and further, the diffusion zone should be relatively

free of reaction products for the enamel-metal system to retain good adherence

after exposure to chemical solutions or to weathering. Round-robin testing of

6063 aluminum alloy extrusions indicated that this alloy can be enameled if care is exercised in the selection of the enamel and the pretreatment

.

17. KEY WORDS (six to twelve entries; alphabetical order: capitalize only the first letter of the first key word unless a proper name; separated by semicolons)

Adherence; aluminum; electron microprobe; electron microscope; porcelain

enamel; spalling; X-ray diffraction.

18. AVAILABILITY X! Unlimited

I For Official Distribution. Do Not Release to NTIS

I X ^ Order From Sup. of Doc, U.S. Government Printirae Office Washington, D.C. 20402, SD Cat. No. C13 29 /? -.5 9 -

I

! Order From National Technical Information Service (NTIS)

Springfield, Virginia 22151

19. SECURITY CLASS

(THIS REPORT)

UNCL ASSIFIED

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

21. NO. OF PAGES

^5

22. Pri,ce Lc $1 . 30.

USCOMM-DC 29042-P74
ANNOUNCEMENT OF NEW PUBLICATIONS IN

BUILDING SCIENCE SERIES

Superintendent of Documents,

Government Printing Office,

Washington, D.C., 20402

Dear Sir:

Please add my name to the announcement list of new publications to be

issued in the series: National Bureau of Standards Building Science Series.

Name

Company

Address

City State Zip Code

(Notification key N-339)



NBS TECHNICAL PUBLICATIONS

PERIODICALS JOURNAL OF RESEARCH reports National Bureau

of Standards research and development in physics,

mathematics, and chemistry. Comprehensive scientific papers g-ive complete details of the work, including- laboratory data, experimental procedures, and theoretical and mathematical analyses. Illustrated with photographs, drawings, and charts. Includes listings of other NBS papers a§ issued. Published in two sections, available separately:

• Physics and Chemistry (Section A)

Papers of interest primarily to scientists working i*i these fields. This section covers a broad range of physical and chemical research, with major emphasis on

standards of physical measurement, fundamental constants, and properties of matter. Issued six times a

year. Annual subscription: Domestic, $17.00; Foreign,

$21.25. • Mathematical Sciences (Section- B)

Studies and compilations designed mainly for the mathematician and theoretical physicist. Topics in mathematical statistics, theory of experiment design, numerical analysis, theoretical physics and chemistry, logical design and programming of computers and computer

systems. Short numerical tables. Issued quarterly. Annual subscription: Domestic, $9.00; Foreign, $11.25. mMENSIONS/NBS (formerly Technical News Bulletin) —This monthly magazine is published to inform

scientists, engineers, businessmen, industry, teachers,

students, and consumers of the latest advances in science and technology, with primary emphasis on the work at NBS. DIMENSIONS/NBS highlights and reviews such

issues as energy research, fire protection, building

technology, metric conversion, pollution abatement,

health and safety, and consumer product performance.

In addition, DIMENSIONS/NBS reports the results of Bureau programs in measurement standards and techniques, properties of matter and materials, engineering

standards and services, instrumentation, and automatic

data processing.

NONPERIODICALS Monographs—Major contributions to the technical liter- ature on various subjects related to the Bureau's scientific, and technical activities. Handbooks—Recommended codes of engineering and

industrial practice (including safety codes) developed

in cooperation with interested industries, professional

organizations, and regulatory bodies. Special Publications—Include proceedings of high-level national and international conferences sponsored by

NBS, precision measurement and calibration volumes,

NBS annual reports, and other special publications

appropriate to this grouping such as wall charts and

bibliographies.

Applied Mathematics Series-^Mathematical tables, manuals, and studies of special interest to physicists, engineers, chemists, biologists, mathematicians, computer programmers, and others engaged in scientific and technical work.

National Standard Reference Data Series—Provides

quantitative data on the physical and chemical properties of materials, compiled from the world's literature and critically evaluated. Developed under a world-wide program coordinated by NBS. Program under authority

of National Standard Data Act (Public Law 90-396).

Building Science Series—Disseminates technical infor- mation developed at the Bureau on building materials, components, systems, and whole structures. The series presents research results, test methods, and performance criteria related to the structural and environmental functions and the durability and safety characteristics of building elements and systems. Technical Notes—Studies or reports which are complete

in themselves but restrictive in their treatment of a

subject. Analogous to monographs but not so comprehensive in scope or definitive in treatment of the subject area. Often serve as a vehicle for final reports of work performed at NBS under the sponsorship of other government agencies.

Voluntary Product Standards—Developed under pro- cedures published by the Department of Commerce in Part 10, .Title 15, of the Code of Federal Regulations. The purpose of the standards is to establish nationally

recognized requirements for products, and to provide

all concerned interests with a basis for common understanding of the characteristics of the products. The

National Bureau of Standards administers the Voluntary Product Standards progi-am as a supplement to the activities of the private sector standardizing

organizations. Federal Information Processing Standards Publications (FIPS PUBS)—Publications in this series collectively constitute the Federal Information Processing Standards Register. The purpose of the Register is to serve

as the official source of information in the Federal Gov- ernment regarding standards issued by NBS pursuant

to the Federal Property and Administrative Services Act of 1949 as amended. Public Law 89-306 (79 Stat. 1127), and as implemented by Executive Order 11717

(38 FR 12315, dated May 11, 1973) and Part 6 of Title 15 CFR (Code of Federal Regulations). FIPS PUBS

will include approved Federal information processing standards information of general interest, and a complete index of relevant standards publications. Consumer Information Series—Practical information, based on NBS research and experience, covering areas

of interest to the consumer. Easily understandable language and illustrations provide useful background

knowledge for shopping in today's technological

marketplace.

NBS Interagency Reports—A special series of interim

or final reports on work performed by NBS for outside sponsors (both government and non-government). In

general, initial distribution is handled by the sponsor;

public distribution is by the National Technical Infor- mation Service (Springfield, Va. 22151) in paper copy

or microfiche form. Order NBS publications (except Bibliographic Subscription Services) from: Superintendent of Documents, Government Printing Office, Washington, D.C. 20402. BIBLIOGRAPHIC SUBSCRIPTION SERVICES

The following current-awareness and literature-survey

bibliographies are issued periodically by the Bureau:

Cryogenic Data Center Current Awareness Service

(Publications and Reports of Interest in Cryogenics).

A literature survey issued weekly. Annual subscription: Domestic, $20.00; foreign, $25.00. Liquefied Natural Gas. A literature survey issued quarterly. Annual subscription: $20.00. Superconducting Devices and Materials. A literature survey issued quarterly. Annual subscription: $20.00. Send subscription orders and remittances for the preceding bibliographic services to the U.S. Department

of Commerce, National Technical Information Sers'-

ice, Springfield, Va. 22151. Electromagnetic Metrology Current Awareness Service (Abstracts of Selected Articles on Measurement

Techniques and Standards of Electromagnetic Quantities from D-C to Millimeter-Wave Frequencies).

Issued monthly. Annual subscription: $100.00 (Special rates for multi-subscriptions). Send subscription order and remittance to the Electromagnetic Metrol- ogy Information Center, Electromagnetics Division, National Bureau of Standards, Boulder, Colo. 80302.
U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Washington, D.C. 20234

OFFICIAL BUSINESS

POSTAGE AND FEES PAID

U.S. DEPARTMENT OF COMMERCE

COM-215

Penalty for Private Use, $300