NBSIR 76-1166

\ STRESS CORROSION BEHAVIOR OF

X7050-T76351 ALLOY ALUMINUM

PLATE

B. T. Sanderson and W. F. Gerhold

Corrosion and Electrodeposition Section

Metallurgy Division

Institute for Materials Research

National Bureau of Standards

Washington, D. C. 20234

November 1976

Final Report

Prepared for Naval Air Systems Command

Department of the Navy

Washington, D. C. 20350

^ r 0„ / V \ • *

U.S. DEPARTMENT OF COMMERCE, Elliot L. Richardson, Secretary

Edward O. Vetter, Under Secretary

Dr. Betsy Ancker-Johnson, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler. Acting Director

STRESS CORROSION BEHAVIOR OF X7050-T76351 ALLOY

ALUMINUM PLATE

By

B.T. Sanderson and W.F. Gerhold

Corrosion and Electrodeposition Section

Metallurgy Division

Institute for Materials Research

National Bureau of Standards

Washington, D.C. 20234

Reference : (a) Naval Air Systems Command, Department of the Navy, Request by

AIR-52031, January 20, 1972.

Introduction

It was requested by Reference (a) that NBS conduct tests to determine the

stress-corrosion behavior of X7050-T76351 aluminum alloy plate in a marine

atmosphere environment.

rfaterial

A section of X7050-T76351 aluminum alloy plate [12 in. (30.5 cm) x 2 in.

(5.1 cm) x 4-1/2 in. (11.4 cm)] was obtained from the Naval Air Development

Center, Warminster, Pa. Specimens in the form of flat tensile bars were

machined from this plate so that the principal axes of the specimens were in

the transverse direction with respect to the direction of rolling of the plate.

The tensile specimens were approximately 9 in. (22.86 cm) long by 1 in. (2.54 cm)

wide by 0.125 in. (.32 cm) thick.

Mechanical Properties

Tests were performed by NBS to determine the transverse mechanical propertie

of X7050-T76351 alloy plate. The results of these tests are shown in Table 1.

Stress-Corrosion Tests

Stressed and unstressed specimens were exposed in the marine atmosphere

at Kure Beach, N.C. [80-foot (24 m) lot]. A system of weights and levers was

used to obtain the desired stress. For the stressed specimens, the applied
.
stress was equivalent to 50 and 75# of the yield strength of the alloy as

\ determined by NBS.

Results

Test results shoxv that none of the X7050-T73651 alloy specimens had

failed after exposure in the marine atmosphere for a period of 756 days.

In order to obtain some indication of the effect of corrosion attack on

the alloy, a comparison was made of the tensile strength of specimens not

exposed to the corrosive environment vs. that of specimens exposed to the

marine environment. The values obtained were then averaged for each

condition and stress level and calculated as the percent loss in tensile

strength due to exposure in the environment. These test results, given in

Table 2, indicate a small average loss (less than 10%) in tensile strength

for the exposed specimens.

Conclusions

The results obtained from stress corrosion tests on X7050-T73651 aluminum

alloy plate indicate that the alloy is resistant to stress corrosion cracking

in a marine atmosphere environment. There were no failures after exposure for

756 days. However, the alloy does exhibit a considerable amount of shallow

surface pitting, accompanied by heavy adherent light gray corrosion products.

This surface pitting and corrosion resulted in an average loss in strength of

less than 10 percent.

Table 1

Transverse Mechanical Properties of X7050-T73651 Aluminum Alloy Platea

Tensile Strength Yield Strength

(0.2% offset) Ksl(k)

Percent Elongation

in 2 in.

75.9 ± 2.1 67.2 ± 1.5 8.2 ± 1.

a

Average of three specimens with standard deviations.

b

l Ksi = 6.89^8 MPa

T&ble

2.

Results

Obtained

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U.S. DEPT. OF COMM

BIBLIOGRAPHIC DATA

SHEET

1. PUBI.K A 1 ION OR R 1 POR I NO. NBSIR 76-1166

2. Gov *t Ac< ession

No.

3. Ret ipient's Accession No.

4. TITLE AND SUB I 1 1 1.1 Stress Corrosion Behavior of X7050-T76351 Alloy

Aluminum Plate

i

5. Publication Date

6. Performing Organization ( ode

7. AUTHOR(S)

R. T. Sanderson and W. F. Gerhold

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 Una No. 3120410

11. Contract/Grant No.

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

Naval Air Systems Command

Department of the Navy

Washington, D.C. 20360

13. Type of Report & Period Covered

14. Sponsoring Agency (.ode

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most significant information. If documen t includes a significant

bibliography or literature survey, mention it here.)

Short transverse tensile specimens of X7050-T76351 aluminum alloy were stressed at

fifty and seventy-five percent of the alloy's yield strength and exposed in a marine atmosphere environment. After seven hundred and fifty-six days, there were

no failures. X7050-T7 6351 alloy appears to be resistant to str-ss corrosion cracking

in this environment.

\

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

)

Alloy; Aluminum; Atmosphere; Marine; Mechanical properties; Plate; Stress corrosion

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