NBSIR 73-133

Performance of Anodized and Chemically

Surface Treated Aluminum Alloy

Rivets in a Marine Environment

E. Escalante, W. F. Gerhold

Corrosion and Electrodeposition Section

Metallurgy Division

Institute for Materials Research

National Bureau of Standards

Washington, D. C. 20234

March 1973

Final Report

Bureau of Aeronautics (Naval Air Command)

Department of the Navy, Letter, Aer-AE-417/89

dated 19 March 1957

Prepared for Materials Division

Naval Air Systems Command

Department of the Navy

Jefferson Plaza BIdg 2

Room 1000

Washington, D. C. 20360

NBSIR 73-133

PERFORMANCE OF ANODIZED AND CHEMICALLY

SURFACE TREATED ALUMINUM ALLOY

RIVETS IN A MARINE ENVIRONMENT

E. Escalante, W. F. Gerhold

Corrosion and Electrodeposition Section

Metallurgy Division

Institute for Materials Research

National Bureau of Standards

Washington, D. C. 20234

March 1973

Final Report

Bureau of Aeronautics (Naval Air Command)

Department of the Navy, Letter, Aer-AE-417/89

dated 19 March 1957

Prepared for Materials Division

Naval Air Systems Command

Department of the Navy

Jefferson Plaza BIdg 2 Room 1000

Washington, D. C. 20360

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

NATIONAL BUREAU OF STANDARDS. Richard W. Roberts. Director
i
PERFORMANCE OF ANODIZED AND CHIiMICALLY SURFACE TREATED

ALUMINUM ALLO^ RIVETS IN A MARINE ENVIRONI^ENT

E. Escalante and W. F. Gerhold

Reference : (a) Bureau of Aeronautics (Naval Air Systems Command)

,

Department of the Navy, Letter, Aer-AE-417/89 , dated

19 March 1957.

Introduction : Military Specification MIL-R-5674 permits the use of MIL-A8625 anodic treatment or MIL-C-5541 chemical surface treatment on aluminum

alloy rivets. Questions have arisen with respect to the protective ability

of the surface treatments after the rivets have been driven or after having

been heat treated and driven.

Reference (a) requested that an investigation be initiated to determine the relative protective ability of anodized and chemical surface

treatments on aluminum alloy rivets after they have been driven. It was

stipulated that painted and unpainted aluminum alloys be exposed in tidal

immersion.

Materials and Specimen Preparation : Subassembly specimens fabricated

from aluminum alloy sheet material were prepared. The alloys used were

as follows:

Aluminum alloy 2219-T6

Clad aluminum alloy 2219-T6

Aluminum alloy 2024-T4

Clad alxaminum alloy 2024-T4

Aluminum alloy 7075-T6

Clad aluminum alloy 7075-T6

Each of the subassembly specimens were prepared by drilling 16 holes through

each at one end of the long dimension. The holes were spaced 1 inch from

-2-

each other and 1/2 inch from the edges. T\-io pieces of the same alloy were

then overlapped at the drilled areas and riveted together to form an

integral assembly 4 inches wide and 12 inches long. Figure 1 is a sketch

illustrating a typical assembly. The rivet alloys and the surface treatments applied to each of the rivets are given in Table 1

.

Five assemblies were fabricated from each of the alloys given above.

Each alloy was divided into two lots, one lot consisting of three specimens

to be exposed unpainted and the other lot consisting of two specimens to

be exposed painted. The paint system on the latter was applied in accordance with Military Specification MIL-F-18264.

Exposures : All specimens were exposed to seawater in the tidal zone at

Harbor Island, North Carolina. The specimens were totally immersed at

high tide and totally out of the water at low tide. Periods of exposure

were for approximately 15 months, 27 months, and 79 months.

Results : An on-site inspection of the specimens was made after 91 days '

exposure. It was noted that two 2219-T4 aluminum alloy rivets had failed.

One, an uncoated rivet, had been driven in an unpainted clad 2219-T6

aluminum alloy specimen; the other, with an Alumilite No. 205 treatment,

had been driven in an unpainted 2024 -T4 aluminum alloy specimen. Paint

failures were observed on all 2219-T4 aluminum alloy rivets driven in

7075-T6 and clad 2024-T4 aluminum alloy specimens. Similarly, paint

failures were noted on 21 17-aluminum alloy rivets driven in clad 2024-T6

aluminum alloy specimens. Other scattered paint failures were also observed on other aluminum alloy rivets; however, no general trend was observed.
i.
-3-

One complete set of aluminum alloy sheet specimens consisting of one

of each of the unpainted specimens of each alloy system were removed from

test after approximately 15 months' exposure. A second and third set of

specimens, each set consisting of one unpainted and one painted specimen

from each alloy system, were removed from test after exposure for approximately 27 months and 79 months.

All specimens were cleaned by scrubbing with a bristle brush to remove loosely adhering material. A wood scraper was used where necessary

to remove fouling. Specimens were then rinsed in clear water and dried.

The unpainted specimens were further cleaned in concentrated nitric acid

to remove corrosion products.

All specimens were examined visually for estimations of deterioration

from corrosion. The results obtained for each rivet alloy are given in

Tables 2, 3, 4, and 5.

In general 2219 aluminum alloy rivets exhibit the same degree of

corrosion whether anodized or chemically surface treated. Rivets fabricated from this alloy and driven in 2024-T4 or clad 2219-T6 aluminum alloy

specimens failed at the rivet head areas, possibly as a result of tensile

failure due to corrosion product build-up at the faying surfaces of the

aluminum alloy sheet subassemblies. However, some of these rivets had

failed prior to the inspection after exposure for approximately 3 months.

The 2017 aluminum alloy rivets which had been given the Iridite 14

treatment exhibited very good resistance to corrosion after approximately

27 months' exposure. After exposure for approximately 79 months all 2017

aluminum alloy rivets were equally corroaed (Figure 2) . However, i;i

general, the 2017 aluminum alloy rivets showed good resistance to corrosion whether coated or not coated.

With some exceptions, bare or surface treated 2117 aluminum alloy

rivets showed good resistance to corrosion. When driven in the 2024 -T4

aluminum alloy sheet, these rivets were found to be pitted and badly corroded after exposure for approximately 27 months. This is shown in

Figure 3. The rivets given the Alumilite 205 treatment exhibited the

least attack while the bare, uncoated rivets had developed shallow pitting

and all of the rivets which were given Alodine 1200 including those given

the reheat treatment were deeply pitted.

Of the 2024 aluminum alloy rivets, those which had been given the

special (stabilizing) heat treatment and were driven uncoated were found

to be more susceptible to corrosion than either the non-stabilized uncoated rivet or the non-stabilized rivet given the Alumilite treatment

205 (Figure 4)

.

An evaluation of galvanic effects between the various aluminum alloy

rivets and the aluminum alloy sheet specimens was made with considerations

given only to short range effects (localized pitting) . Table 6 contains

the dissimilar metal couples evaluated. These are classified on the basis

of what was corroded and what was protected.

In general, the effects of coupling were less obvious on the clad

material as compared to the unclad material. With the exception of the

clad 2219-T6 aluminum alloy sheet material where pitted areas were noted

adjacent to the anodized 2017 and the 2219 aluminum alloy rivets, the

cladding appeared to substantially reduce the crevice corrosion at the

faying surfaces of the aluminum alloy sheet materials. This is shovvn in

Figures 5 and 6.

-5-

Without exception, corrosion was substantially reduced on specimens

that had been painted. In some cases there was no apparent corrosion.

Summary: Tests were conducted in the seawater in the tidal zone to determine the relative protective value of anodized and chemical surface treatments on aluminum alloy rivets after they have been driven. Rivet materials

studied included 2219-T4, 2017- , 2117- , and 2024- aluminum alloys. Surface

treatments studied were Alumilite No. 204 and No. 205, Alodine 1200,

Irilac, and Iridite No. 14. Rivets were driven in 4 -inch x 12-inch

specimens fabricated from the following materials:

Clad and unclad 2219-T6 aluminum alloys

Clad and unclad 2024-T4 aluminum alloys

Clad and unclad 7075-T6 aluminum alloys

The results of visual examinations of specimens exposed for periods

of up to approximately 79 months revealed the following:

(1) The Iridite 14 chemical surface treatment did provide good

protection to the 2017 aluminum alloy rivets during the first 2 to 3 years.

However, there was little difference between the protective ability of the

anodized vs chemical surface treatments after 79 months exposure.

(2) For the Alodine 1200 surface treatments on the 2117 aluminum

alloy rivet reheat treatment after surface treatment increased its

susceptibility to corrosion.

(3) The stabilizing heat treatment given the 2024 aluminum alloy

rivet increased its susceptibility to corrosion in many cases but not

all

.

(4) An evaluation was made of tlie galvanic effects between the

various rivets and the aluminum alloy sheet (dissimilar metal couples)

.

-6-

It was noted that the effect was more pronounced between the following:

(a) Stabilized 2024 aluminum alloy rivets driven in bare 2219-T6

and 2024 T4 aluminum alloy sheet specimens;

(b) 2117 aluminum alloy rivets driven in bare 2024 -T4 aluminum

alloy sheet specimens.

There was little or no galvanic effect between aluminum alloy rivets driven

in 7075 -T6 aluminum alloy sheet specimens.

(5) Cladding reduced corrosion effects particularly at the faying

surface.

(6) The painted specimens showed substantially reduced corrosion.

Table 1. Rivet Alloys and Surface Treatments

Applied to Each of the Rivets.

Rivet Alloy Surface Treatment

2219-T4 None

Alumilite No. 205

Alodine No. 1200

Irilac

Iridite No. 14

2017^^-^ None

Alumilite No. 205

Alumilite No. 204

Iridite N-. 14

2117^^^ None

Alumilite No. 205

Alodine No. 1200 ,,. , . Alodine No. 1200'- ''

2024^^-' None

Alumilite No. 205

None, special heat

treatment (c)

(a) Condition unknown

(b) Reheat treated after surface treatment

(c) Special stabilizing treatment which reportedly makes

unnecessary the solution heat treatment normally used

prior to being driven. Details of heat treatment

unknown

.
1
Table 2. Evaluation of Rivet Alloy 2219-T4 after Exposure

in the Seawater for Number of Days Shown.

Rivet Surface Treatment

Panel Alloy None Alumilite Special Heat Alodine Alumilite Irilac Iridite Alodine Exposure

and (Uncoated) No. 205 Treatment

,

No. 1200 No. 204 No. 14 1200 (3) Time

Treatment Bare (Days)

2219-T6, bare d a a a a 455

M It d b b- b b 811

IT M b b b b b 2373

2219-T6, painted ga ga ga ga ga 811

ti ti ga ga d d gb 2373

Clad 2219-T6, bare b a d a d 455

ft rr II a d d d a 811

ti fi ti d d d d a 2373

Clad 2219-T6, painted ga ga ga ga ga 811

It M tl ga ga ga ga ga 2373

2024 -T4, bare ad^^^ ad^^) ad^^) adf'^^ d 455

It II d d d d b 811

n n d d d d d 2373

2024-T4, painted ga ga ga ga ga 811

II It ga ga ga ga ga 2373

Liaa ^uzH-i'i-, Dare a a a a a 455

It It 11 a a a a a 811

M II It a a a a a 2373

Liau 4iuz4-i4, painted ga ga ga ga ga 2373

II II II Lost from

racks

7075-T6, bare b d d a a 455

11 II a a a a a 811

tt II a a a a a 2373

7075-T6, painted ga ga ga ga ga 811

If II ga ga ga ga ga 2373

Clad 7075-T6, bare b a a a a 455

M tl It a a a a a 2373

It II II Lost from

racks Clad 7075-T6, painted Lost from racks

II tl IT ga ga ga ga ga 2373

(1) (a) No corrosion

(b) Scattered shallow corrosion pits

(c) Scattered medium deep corrosion pits

(d) Rivet head cracked

(e) Driven head of rivet cracked

(f) No paint failures at rivet heads

(g) Paint failures at rivet heads

(h) General shallow corrosion attack

(i) General corrosion attack

(2) Heat treated, condition unknown

(3) Reseat treated after application of surface treatment

(43 Rivet cracked but still attached

I

(2) Table 3. Evaluation of Rivet Alloy 2017^ ' after Exposure

in the Seawater for Number of Days Shown.

Bare txLumx X1X.G Alunii 1 i te 1 X J.UX L C Days and No. 205 No. 204 No. 14 Exposed

Treatment

a 3. a a /I t:

II 11 ho hu uu Oil

ti n b a a a 2373

2219-T6, painted 5<* cr A 81

1

II 11 ga ga ga ga 2373

a b a 455

If II II a 811

11 II II a ec e a 2373

Clad 2219-T6, painted pa Q3. pa 811

11 It II ga ga ga ga 2373

2024-T4, bare b b a 455

It II b b b b 811

fi II b d b b 2373

2024-T4, painted ga ga ga 6** ea 811

11 ti pa pa pb 2373

Clad 2024-T4, bare a b a a 455

tt II II a oX X

It II II a a a 2373

Clad 2024-T4, painted ga ga ga ga 2373

II II II racks

7075-T6, bare b a b HOJ

II II 3. 3, R1oil1 It ti a a a 2373

7075-T6, painted ga ga ga ga 811

It II sa pa &<* 2373

Clad 7075-T6, bare a b a a 455

11 II II a a a a 2373

It II It Lost from

racks Clad 7075-T6, painted Lost from

It II II racks ga ga ga ga 2373

(1) No corrosion Scattered shallow corrosion pits

Scattered medium deep corrosion pits

Rivet head cracked

Driven head of rivet cracked

No paint failures at rivet heads

Paint failures at rivet heads

General shallow corrosion attack

General corrosion attack

(2) Heat treated, condition unknown

(3) Reheat treated after application of surface treatment

(4) Rivet cracked but still attached

Table 4. Evaluation of Rivet Alloy 2117^ after Exposure

in the Seawater for Number of Days Shown.

Panel Alloy

and Treatment

Bare Alumilite

No. 205 AlodineNo. 1200 Alodine

No. 1200(.3J Days

Exposed

2219-T6 bare h 455

Tl II b b b b 811

II II b b b b 2373

2219-T6, painted ga ga ga ga 811

II II ga gb ga ga 2373

Clad 2219-T6, bare 3 a 455

II II II a a b a 811

II II II a a a a 2373

Clad 2219-T6, painted ga ga ga ga 811

II II II ga ga ga ga 2373

2024-T4 bare c b b 455

II II c c h 811

II II c ce ie ie 2373

2024 -T4, painted 5** 8** 811

II II gb d gb gb 2373

Clad 2024-T4, bare b a 455

II 11 II a 811

II II II a a a a 2373

Clad 2024-T4, painted fib ea Ba 2373

II II 11 Lost from

racks

7075-T6, bare b b b 455

II II Au 811

II 11 a a d a 2373

7075-T6, painted ga ga 8* 811

II II ga ga 2373

Clad 707S-T6, bare a b a b 455

11 II II a a a a 2373

II II II r Lost from

racks

Clad 7075-T6, painted Lost from

racks

II II II ga gb ga ga 2373

(1)

(a) No corrosion

(b) Scattered shallow corrosion pits

(c3 Scattered medium deep corrosion pits

(d) Rivet head cracked

(e) Driven head of rivet cracked

(f) No paint failures at rivet heads

(g) Paint failures at rivet heads

(h) General shallow corrosion attack

(i) General corrosion attack

(2) Heat treated, condition unknown

(3) Reheat treated after application of surface treatment

(4) Rivet cracked but still attached

f21 Table 5. Evaluation of Rivet Alloy 2024^ ' after Exposure

in the Seawater for Number of Days Shown.

Pan^^l Allnv Bare r\Aliimilil'p X. Uill-L X -1- D3.y s and No. 205 Treatment

,

Exposed

Treatment Bare

2219-T6, bare I, 455

5 811

ti If b b i 2373

2219-T6, painted &** eb 811

n It ga ga gc 2373

Clad 2219-T6, bare I) 455

II II II I) 811

II II II a a b 2373

Clad 2219-T6, painted 6** 811

II II II ga ga ga 2373

2024-T4, bare Au aeC'*^

. 455

ti II b de 811

ti II b b de 2373

2024-T4, painted ea ea 811

II 11 era 6"* 2373

Clad 2024-T4, bare a a a 455

II II II a a a

Q 1 1 Oil

II II II 3, 2373

Clad 2024-T4, painted ga ga ga 2373

II II II Lost from

racks

7075-T6, bare b b b 455

II If ad(^) 811

ti If 3, 3, a. 2373

7075-T6, painted ga ga ga 811

M It 6" ga ga 2373

Clad 7075-T6, bare a a a 455

II II II a a a 2373

II II II Lost from

racks

Clad 7075-T6, painted Lost from

racks ga ga ga 2373

(1)

(a) No corrosion

(b) Scattered shallow corrosion pits

(c) Scattered medium deep corrosion pits

(d) Rivet head cracked

(e) Driven head of rivet cracked

(f) No paint failures at rivet heads

Cg) Paint failures at rivet heads

Ch) General shallow corrosion attack

(i) General corrosion attack

(2) Heat treated, condition unknown

(3) Reheat treated after application of surface treatment

(4) Rivet cracked but still attached

Table 6. Dissimilar Metal Effects

Rivet Alloy

2024 - slightly protected

2024 - no effect

2024 - slightly protected

2024 (stabilized) - attacked

2024 (stabilized) - attacked

2024 (stabilized - protected

2219-T4 - slightly protected

2219-T4 - no effect

2219-T4 - no effect

2017 - protected

2017 - no effect

2017 - protected

2117 - slightly protected

2117 - attacked

2117 - no effect

Coupled to Sheet Alloy

2219-T6 - attacked

2024-T4 - no effect

7075-T6 - very slight attack

2219-T6 - protected

2024 -T4 - protected

7075 -T6 - slight attack

2219-T6 - slight attack

2024-T4 - no effect

7075 -T6 - no effect

2219-T6 - attacked

2024-T4 - no effect

7075 -T6 - slight effect

2219-T6 - slight attack

2024-T4 - protected

7075 -T6 - no effect
I

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Figure 2. Appearance of 2017 Aluminum Alloy Rivets in Clad

2219-T6 Aluminum Alloy Sheet after Approximately

79 Months Exposure in Tidal Immersion at Harbor

Island, North Carolina. X3.3

a) Bare

b) Coated, Alumilite 205

c) Coated, Alumilite 204

d) Coated, Iridite 14
I
Appearance of 2117 Aluminum Alloy Rivets in Bare

2024 Aluminum Alloy Sheet after Approximately 27

Months Exposure in Tidal Immersion at Harbor

Island, North Carolina. X3.3

a) Bare

b) Coated, Alumilite 205

c) Coated, Alodine 1200

d) Coated, Alodine 1200 Reheat Treated

c

Figure 4. Appearance of 2024 Aluminum Alloy Rivets in Bare

2024-T4 Aliiminum Alloy Sheet after Exposure Indicated in Tidal Immersion at Harbor Island, North

Carolina. X3.3

a) Bare, 27 Months

b) Bare, Stabilizing Heat Treatment, 15 Months

c) Coated, Alumilite 205, 15 Months

Figure 5. Appearance of Faying Surface of Bare 2024 -T4 Aluminum

Alloy Sheet after Exposure for 79 Months in Tidal Immersion at Harbor Island, North Carolina. X 1

Figure 6 Appearance of Faying Surface of Clad 2024-T4 Aluminuin

Alloy Sheet after Exposure for 79 Months in Tidal Immersion at Harbor Island, North Carolina. X 1

I OF<M NBS-11'{A (1-71) U.S. DLPT. OF COMM. 1. FUBLICATION OR REPORT NO. 2. Gov't Accts.sion E*''^L10GRAPHIC DATA j^^gjj^ No.

3. Recipient's Accession No.

' I'lTi.li AND SUK l l I I I-,

Perf. ruiance of Anodized and Clicmically Surface Ircatod

Muiiiinuin Alloy Rivets in a Marine Environment

5. l-'ublicaiimi D.ue

0. Pc I fonmng (X^'.^^ni/utioii C-(»Jc

7. AUl llOR(S) ,

, , , E, Escalante and W. F. Gerhold

8. P<.r forming; C): /•..inizatiori NBSIK 73-133

9. FI;R1-0RMING organization NAM)^ and ADDR['SS

NA'l lONAI, BURKAU OF STANDARDS

departmi:;nt of commerce

washington, d.c. 20234

10. l'ri>)( Ci/'l"a.sk, Work Unit Nr.. 3120410

11. Contract/Grant No.

12. Sponsoring Organization Name and Address

Bureau of Aeronautics

ivavai /vir oystems GOJiuiiana

Department of the Navy

13. Type of Rcpcrt & Period

<-overed

14. Sp.onsoring Aj'-.ency Code

15. SUPPLEMENTARY NOTES

16. Ai>S'l 1', Av.'l (A ?00-word or less factual SLUiimary of most significant informat joiu If docunicin includes a bignificjtnt

bibliogra[.hy or litcrarure survey, mention it here.) This is a report on the results of a corrosion study of surface treated aluiuinum

alloy rivets on aluminum alloy sheet in a tidal zone environri:cnt . Tlic rivet allc)'s

investigated were 2024-, 202^1- (stabilized), 2219-T4, 2017-, and 2117-. The sheet

alloyj investigciteG were 2219-T6, 2024-T4, and 7075-T6 in the clad and unclad

condition. Various combinations of the rivet -sheet alloys v.ere exposed bare or

painted.

Results indicate little difference between chemical coatings or anodizing treatments

of tlie rivets after three years exposure. The stabilizing lieci. troatmciit on 2024-

incrcases its susceptibility to corrosion in most cases. Galvanic couples can lead

to sej-ious corrosion problems. However, cladding substanti all)- reduces this effect.

Paint coatings on the specimens did effectively reduce con'osion in all cases.

17. KEY TORDS (Alphabetical orde,, separated by semicolons^ Aluminum allo>s; anodizcd; chemically

suifacc treated; corrosion; rivets

'B. AVAIL.-' r.IiJTY STATEMENT

UNLIMLI ElJ.

[Xj 1-OR Ol-nCIAL DLSTRlBUriON. DO NOT RELEASE

'10 N T IS.

T?'. SE; -liKiTY CLA>

(Til IS REPORT)

UNCI. ASSILIFT)

20. SECURITY CLASS

(THIS PAGE)

I UNCI- AS.SII IEI)

2i. NO. Oi- PAGi22

22. Price