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QUARTERLY STATUS REPORT FOR THEQUARTER ENDING APRIL 3 O, 1S66 ON

NBS PROJECT 3I20‘^.45

INVESTIGATION OP THL DIRECTIONAL EFFECTS

IN THE STRESS CORROSION OF ALUMINUM ALLOYS

oy

Hugh L. Logo

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Gilbert 1-1

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Ugiaaskyo i '-Cj

S. W'ay.ie Stiefel

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for

National Aeronautica and Space AdministrationGeorge C. Marshrl. Space Flight Center

Huntsviile, Alabama

Contract H-2151AControl 1-6-54-01046-01 (IF)

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THE NATiONAL BUREAU OF STANDARDS

The National Bureau of Standards is a principal ioca! point in the Federal Government for assur-

ing maximum application of the physical and engineering sciences to the advancement of technologyj

in industry and commerce. Its responsibilities include development and maintenance of the nationalj

standards of measurement, and the provisions of means for making measurements consistent with 1

those standards; determination of physical constants and properties of materials; development ofJ

methods for testing materials, mechanisms, and structures, and making such tests as may be neces- 1

sary. particularly for government agencies; cooperation in the establishment of standard practicesj

for incorporation in codes and specifications: advisory service to government agencies on scientific;]

and technical problems; invention and development of devices to serve special needs of the Govern-

ment; assistance to industry, business, and consumers in the development and acceptance of com-

mercial standards and simplified trade practice recommendations; administration of programs in

cooperation with United States business groups and standards organizations for the development

of international standards of practice; and maintenance of a clearinghouse for the collection and

dissemination of scientific, technical, and engineering information. The scope of the Bureau’s

activities is suggested in the following listing of its three Institutes and their organizational units.

Institute for Basic Standards. Applied Mathematics. Electricity. Metrology. Mechanics. Keat.

Atomic Physics. Physical Chemistry. Laboratory Astrophysics.* Radiation Physics. Radio Standards ,

Laboratory:* Radio Standards Physics; Radio Standards Engineering. Office of Standard Reference

Data.

Institute for Materials ResearcL. Analytical Chemistry. Polymers. Metallurgy. Inorganic Mate- :

rials. Reactor Radiations. Cryogenics.* Materials Evaluation Laboratory. Office of Standard Refer-

ence Materials. !

Institute for Applied Technology. Building Research. Information Technology. PerformanceTest Development. Electronic Instrumentation. Textile and Apparel Technology Canter. Technical

|

Analysis. Office of Weights and Measures. Office of Engineering Standards. Office of Invention andInnovation. Office of Technical Resources. Clearinghouse for Federal Scientific and Technical

Information.** i

•Located at Boulder, Colorado, 80301.* ‘Located at 5235 Port Royal P.oad, Springfield, Virginia, 22171.

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EvJATlONAL BUREAU OF STAiVJDARDS REPORT

NSS Pf^OJECT

3120A45 Apri L 3'^; 1966

NBS REPORT

9351

QUARTEllLY STATUS REPORT FOR THE QUARTER ENDING 4/30/66

oil

INVESTIGATION OF Tffi DIRECTIONAL EFFECTS

IN THE STRESS CORROSION OF ALUMINUM ALLOYS

by .

Hugh L. Logan

Gilbert M. Ugianskyand

S. Wayne Stiefel

for

National Aeronautics and Space AdministrationGeorge C. Marshall Space Flight Center

Huntsville^ Alabama

Contract H-2151AControl 1-6-54-01046-01 (IF)

IMPORTANT NOTICE

NATIONAL BUREAU OF STANIfor use within the Government. Bef

and review. For this reason, the pu

whole or in part, is not authorized

Bureau of Standards, Washington 2

the Report has been specifically prei

Approved for public release by the

director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015

Kcounting documents intended

jected to additional evaluation

ting of this Report, either in

ffice of the Director, National

Government agency for which

IS for its own use.

U. S. DEPAPiTOENT Of mZSm.

NATIONAL mW OF SIANOAPiOS

This report was prepared by the Corrosion Section^ National Bureau of

Standards under Contract No. H-2151A "Investigation of the DirectionalEffects in the Stress Corrosion of Aluminum Alloys" for the George C.

Marshall Space Flight Center of the National Aeronautics and SpaceAdministration. The work was administered under the technical directionof the Propulsion and Vehicle Engineering Laboratory, Materials Divisionof the George C. Marshall Space Flight Center with D. B. Franklin actingas project manager.

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Anticipated Work

A. Continue stress-corrosion tests for J0Y5 plate material.

B. Continue electronmicrogra ph and microprobe studies.

C. Determine grain size in 3 orientations in JOJS plate material.

D. Complete preferred orientation studies.

Abstract

Macroscopic examinations of the J0J5 and 2219 plate materials have beencompleted and hardness surveys were made through the thickness of thesematerials

.

Both notched and un-notched tensile specimens were machined in threeorientations from the plate materials. Soon after tensile tests werebegun on the 2219 material, it was found to be faulty and was subse-quently recalled by the manufacturer. Studies are in progress to

determine the defect in that material.

Tensile properties were determined for the un-notched J0J5 materials and

the s tress -corrosion tests were begun. Total immersion in a solutioncontaining 0.3% NaCl + 3*0% ^*^^^2*^7 3*0% CrO was found to be superiorto anodic polarization in 3 1/2% NaCl as a s tress -corros ion environment.

Preferred orientation studies of 7075-T651 are nearly completed and

studies of the 70?5-T73 are in progress.

Work Accomplished to Start of Current Reporting Period

The grain flow of a 7075-T6 extrusion was studied to determine areas from

which specimens could be machined and tensile properties were determinedfor both notched and un-notched specimens machined with their axes in the

short transverse direction. The effect of notch radius on the tensileproperties was also studied.

The microstructure of the J0J5-T6 aluminum alloy extrusion was studiedfor different orientations at different distances from the die surface.

Investigation of the Directional Effects on the Stress Corrosion of

Aluminum Alloys

Macroscopic examinations of the 7^75 and 2219 plate materials have beenmade through the thickness of the plate on two planes with respect to the

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direction of rolling, namely, normal to and in the direction of rolling.

Hardness surveys at 1/4 inch intervals were made through the thicknessof the plate on all of these materials. In every case the material in

the center of the plate was softer than that near the surfaces. Thevalues are given in Table 1.

Meta llogra phic and preferred orientations studies are being made onthese materials to confirm the indications of uniformity found in the

hardness studies on plate 2219-T87 and possibly plate 7075-T73 and to

account, if possible, for the decrease in hardness toward the centerof the material' in plates 2219-‘l’37 7075-T651. Subsize round tensilespecimens were machined from these plates (a) with their long axes

normal to the plate surfaoe (short transverse specimens), and (b) withtheir long axes normal to the rolling direction and in the rolling plane

(long transverse specimens), and (c) with their long axes in the directionof rolling of the plate (longitudina'l specimens,) The softer materialfound in the centers of some of these plates is in the reduced sectionsof the short transverse specimens. The long transverse and longitudinalspecimens were machined from layers of material near the centers of the

short axes in the plates so that the entire specimens would be machinedfrom the softer material.

Table 1. Hardness of Plate Specimens(Rockwell B Scale)

Alloy Interior Bottom

2219 T87 79 77 78

2219 T37 68 63 69

7075 T73 82.5 80 83

7075 T651 92 88 92

Top and bottom values were taken 1/4 inch from the two surfaces of the

plate. Interior value was the minimum value recorded and was usually,but not necessarily, that nearest the center of the plate.

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During machining of short transverse specimens from the 2219-T87 plate,three were broken. We attributed this to poor machining technique.However, two notched tensile specimens from a nearby area broke in

tensile test not at the notch, but in a region having 9/4 the area at

the root of the notch and at a stress computed to be 6l00 psi. Thelocation of these fractures was at approximately the same depth belowthe surface of the plate as those in the specimens broken duringmachining as shown with a macroetched cross-section of the plate in

Figure 1. Adjacent short transverse specimens, one of which was sec-tioned longitudinally for meta llogra phic examination, were radiographedand showed some indication of voids or inclusions. Figure 2 is a photo-micrograph of the longitudinally sectioned specimen in the unetchedcondition. The macroconstituents are to be determined with the aid of

the electron microprobe.

The supplier of the 2219 alloy plate has stated that the material was

unsatisfactory, has asked that it be returned and has stated that theyare fabricating new material to replace that being recalled. As of the

date of this report, the replacement material has not been received.

The tensile properties of the 7075-T651 and 70T5-T73 aluminum alloy plate

material were determined in the short transverse, long transverse and

longitudinal directions (Table 2).

Table 2. Tensile Properties of 7075-T651 and

7O75-T73 Plate Materials in the ThreeDirections

SpecimenDesignation

Yield Strength(psi)

Tensile Strength(psi)

T651 Short Transverse 64,300 76,500

t651 Longitudinal 69,500 81,700

T651 Long Transverse 75,600 86,400

T73 Short Transverse 56,300 66,700

T73 Longitudinal 59,400 71,300

T73 Long Transverse 61,600 72,600

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Two test methods were tried to accelerate stress-corrosion. Anodicpolarization using a 3 l/27o NaCl solution produced a great amount ofoverall corrosion with exfoliation. The second method consisted oftotal immersion of the specimen in Alcoa H solution (0.37> NaCl + 3*07o

KgCr^O + 3-07, CrO using distilled water^ solution pH 0.9). The

specimens were ele^ tropolished in a perchloric acid-ethanol soluti(

to remove the worked surface metal..on

All tests were made using 757, of the specimen's yield strength. Timesto failure for the 7075-T651 alloy were 5 minutes for the short trans-verse, 5.5 hours for the long transverse and 10,6 hours for the longi-tudinal specimens. (Preliminary tests - only one specimen tested in

each orientation.) Photomicrographs (Figures 3^ ^ 5) were takenof the short transverse specimens and show the typical stress-corrosioncracks observed. The fractured surfaces are being replicated for

electron microscopy studies. Work is continuing to determine if the

long transverse and longitudinal specimens failed by stress-corrosion.

Preferred orientation studies of the 70T5-T651 are nearly completedand studies of the 70?5-T73 are in progress. An attempt will be madeto correlate the preferred orientation in these materials with the

stress-corrosion susceptibilities of specimens from the variousdirections

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Figure 1

2219-T87 aluminum alloy short transverse specimens 1, 2, and 3

broke during machining. Specimens 4 and 5 broke in tensiletest at a region 9/4 the area at the root of the notch. The

cross-section of the plate was etched with Flick's reagent.X 1.

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Figure 2

Photomicrograph of a 2219-T37 aluminum alloy short trans-verse tensile specimen prior to testing. Photomicrographwas taken at the same level as indicated by fractures in

Figure 1. Unetched X 100

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Figure 3

Photomicrograph of a 7075-T651 aluminum alloy short trans-verse specimen which failed at 757, of its yield strengthafter 5 minutes in Alcoa H solution. Note the intergranularstress-corrosion cracks which start at the pits. Keller'setch X 100

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X 100

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Figure 5

Photomicrograph of a ’J0^5-To51 aluminum alloy short trans-verse specimen which failed at 75% of its yield strengthafter 5 minutes in Alcoa H solution. Note the intergranularstress-corrosion cracks which start at the pits. Comparewith the unetched condition in Figure 4. Keller's etch X 100

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