DEC 2 2 1969

NATIONAL BUREAU OF STANDARDS REPORT

10 137

Progress Report on the

STRESS-CORROSION BEHAVIOR OF DIE

FORGED ALUMINUM ALLOY 7175-T736

To

Materials Division

Naval Air Systems Command

Department of the Navy

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards ' was established by an act of Congress March 3, 1901. Today,

in addition to serving as the Nation’s central measurement laboratory, the Bureau is a principal

focal point in the Federal Government for assuring maximum application of the physical and

engineering sciences to the advancement of technology in industry and commerce. To this end

the Bureau conducts research and provides central national services in four broad program

areas. These are: (1) basic measurements and standards, (2) materials measurements and

standards, (3) technological measurements and standards, and (4) transfer of technology.

The Bureau comprises the Institute for Basic Standards, the Institute for Materials Research, the

Institute for Applied Technology, the Center for Radiation Research, the Center for Computer

Sciences and Technology, and the Office for Information Programs.

THE INSTITUTE FOR BASIC STANDARDS provides the central basis within the United

States of a complete and consistent system of physical measurement; coordinates that system with measurement systems of other nations; and furnishes essential services leading to accurate and

uniform physical measurements throughout the Nation’s scientific community, industry, and commerce. The Institute consists of an Office of Measurement Services and the following technical

divisions:Applied Mathematics—Electricity—Metrology—Mechanics—Heat—Atomic and Molecular Physics—Radio Physics -—Radio Engineering -—Time and Frequency - —Astrophysics -—Cryogenics. 2 THE INSTITUTE FOR MATERIALS RESEARCH conducts materials research leading to im- proved methods of measurement standards, and data on the properties of well-characterized

materials needed by industry, commerce, educational institutions, and Government; develops,

produces, and distributes standard reference materials; relates the physical and chemical properties of materials to their behavior and their interaction with their environments; and provides

advisory and research services to other Government agencies. The Institute consists of an Office

of Standard Reference Materials and the following divisions: Analytical Chemistry—Polymers—Metallurgy—Inorganic Materials—Physical Chemistry.

THE INSTITUTE FOR APPLIED TECHNOLOGY provides technical services to promote

the use of available technology and to facilitate technological innovation in industry and Government; cooperates with public and private organizations in the development of technological

standards, and test methodologies; and provides advisory and research services for Federal, state, and local government agencies. The Institute consists of the following technical divisions and

offices: Engineering Standards—Weights and Measures — Invention and Innovation — Vehicle Systems Research—Product Evaluation —Building Research—Instrument Shops—Measurement Engineering—Electronic Technology—Technical Analysis.

THE CENTER FOR RADIATION RESEARCH engages in research, measurement, and application of radiation to the solution of Bureau mission problems and the problems of other agencies and institutions. The Center consists of the following divisions: Reactor Radiation—Linac Radiation—Nuclear Radiation—Applied Radiation. THE CENTER FOR COMPUTER SCIENCES AND TECHNOLOGY conducts research and

provides technical services designed to aid Government agencies in the selection, acquisition, and effective use of automatic data processing equipment; and serves as the principal focus

for the development of Federal standards for automatic data processing equipment, techniques, and computer languages. The Center consists of the following offices and divisions: Information Processing Standards—Computer Information — Computer Services — Sys- tems Development—Information Processing Technology.

THE OFFICE FOR INFORMATION PROGRAMS promotes optimum dissemination and

accessibility of scientific information generated within NBS and other agencies of the Federal government; promotes the development of the National Standard Reference Data System and a system of information analysis centers dealing with the broader aspects of the National Measure- ment System, and provides appropriate services to ensure that the NBS staff has optimum accessibility to the scientific information of the world. The Office consists of the following

organizational units:

Office of Standard Reference Data—Clearinghouse for Federal Scientific and Technical

Information ' —Office of Technical Information and Publications—Library—Office of Public Information—Office of International Relations.

Headquarters and Laboratories at Gaithersburg. Maryland, unless otherwise noted; mailing address Washington, D.C. 20234.

J Located at Boulder. Colorado N0302.

1 Located at 62H6 Port Royal Road. Springfield. Virginia 22151.
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT

3120410

DEC 2 2 1969 NBS REPORT

10 137

Progress Report on the STRESS-CORROSION BEHAVIOR OF DIE

FORGED ALUMINUM ALLOY 7175-T736

By

W. F. Gerhold

Engineering Metallurgy Section

To

Materials Division

Naval Air Systems Command

Depa rtment of the Navy

IMPORTANT NOTICE NATIONAL BUREAU OF ST A r

for use within the Government. B and review. For this reason, the | whole or in part, is not authorizf Bureau of Standards, Washington,

the Report has been specifically pr

Approved for public release by the

)irector of the National Institute of

standards and Technology (NIST)

on October 9, 2015.

accounting documents intended

ibjected to additional evaluation

isting of this Report, either in Office of the Director. National

the Government agency for which

ies for its own use. <NBS>

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

Progress Report on the

Stress-Corrosion Behavior of Die

Forged Aluminum Alloy 7175-T736

By

W. F. Gerhold

Engineering Metallurgy Section

Reference: (a) Naval Air Systems Command letter,

AIR- 52031A : RS/S3 dated August 16, 1968

I ntroduct ion : A new Alcoa die forged aluminum alloy designated

7175 has been reported to have good stress-corrosion cracking

resistance when heat treated to the -T736 condition. Reference

(a) requested that NBS conduct tests to determine the stress

corrosion behavior of this alloy in artificial laboratory and

marine environments. This report contains the results obtained

from tests conducted in the artificial laboratory environments

only

.

Material : A die forged 7175-T736 aluminum alloy section (Die

No. 9112) approximately 36 in. long was submitted for test by

the vendor. Specimens in the form of flat tensile bars were

machined from this section so that their principal axes were

in the transverse direction with respect to the direction of

working of the forging. The specimens were approximately 3 in.

long by 0.75 in. wide by 0.125 in. thick.

Tensile Properties : The results of tests conducted by NBS to

determine the tens i le properties of the die forged 7175-T736

aluminum alloy are given in Table 1.

(a) Table 1. Transverse tensile properties^ J of die

forged 7175-T736 aluminum alloy

Tensile Strength, ksi 76.5

Yield Strength (0.2% offset), ksi 68.3

Elongation in 1 inch, percent 11.0

(a) Average of three specimens.

Stress -Corrosion Tests : St res s - corros ion tests were conducted

in artificial laboratory environments. A system of weights

and levers was used to obtain the desired stress.

2

The specimens were encased in polyethylene cells which

were used to contain the corroding media. The specimens were

immersed intermittently in the corrodent, once in every 45

minutes, by pumping the corrodent into the cell and then

allowing it to drain back into a reservoir. Two corroding

solutions were used; one a IN sodium chloride solution

containing 10 ml of hydrogen peroxide (30%) per liter of

solution and the other a straight 3.5% sodium chloride

solution. Specimens were exposed in both environments at

stresses equivalent to 75% of the yield strength of the alloy

as determined by NBS. The percent loss in tensile strength

was determined for each specimen to give an indication of the

extent of corrosion. These determinations, shown in Table 2,

revealed that the corrosion rate of the stressed specimens

exposed in the more aggressive NaCl-FbOo solution was higher

than that for stressed specimens exposed in the 3.5% NaCl

solution. The corrosion rates were similar for unstressed

specimens exposed in both environments.

Conclusions : The results obtained from stress -corrosion

conducted in artificial laboratory environments on die fo

7175-T36 aluminum alloy indicate that the alloy has good

resistance to s tress - corros ion cracking.

tests

rged

There were no stress -corrosion failures after

mately 61 days exposure in either the NaCl-l^C^ or

environments

.

approxi

3.5% NaCl

The corrosion rate,

yield strength of the al

environment than in the

rate for unstressed spec

for specimens stressed at 75% of the

loy, was higher in the NaCl-HgOg

3.5% NaCl environment. The corrosion

imens was similar in both environments.

USCOMM-N BS-DC

Table 2. Results obtained from s t res s - cor ros ion tests

conducted in artificial laboratory environments.

Environment Exposure Exposure Days Percent

Stress , % of Yield

Strength

Stress , ks i Exposed f a ) Loss in

Tensile

Strength

3.5% NaC

1

75 51.4 61 NF 17

75 50.9 62 NF 6

75 50 .

9

61 NF

Avg.

12

12

0

- 6 2 NF 5 0

- 62 NF 7 0 6 2 NF

Avg.

6

6

NaCl-H~0 o 75 51 . 4 6] NF 19

Z Lj 75 50.9 61 NF 7 75 50.9 61 NF

Avg .

2 2 16

0

- 61 NF 5 0

- 61 NF 7 0

“ 61 NF

Avg.

3

5

(a) NF indicates no failure after exposure for the number

of days shown.


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