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Stress Corrosion Susceptibility Of Welded Aluminum Alloys

Report Number: AFML TR 67-291
Author: Turley, Richard F.
Author: Avery, Charles H.
Author: Dash, Edward
Corporate Author: Douglas Aircraft Company
Laboratory: Air Force Materials Laboratory
Date of Publication: 1967-08
Pages: 180
Contract: AF 33(615)-5419
Project: 7381
Task: 738107
AD Number: AD0824852

Abstract:
Adequate knowledge of the stress corrosion thresholds of welded aluminum alloys is required by designers to utilize mechanical properties fully. This program determined threshold stress levels for 2014-T6, X2021-T8E31, 2024-T81, 2219-T87, X7002-T6, 7039-T64, and 7106-T6. Variables were sheet and plate, long transverse grain direction, welded and post-weld heat treated, notched and unnotched. Tests were conducted using step load and constant load 500 hours alternate immersion in synthetic sea water at sus­tained stress levels up to 75-percent yield strength. All basic, unwelded alloys, sheet and plate, had thresholds above 75-percent yield strength. Thresholds for unnotched sheet alloys were below 75-percent yield strength for 2014-T6, as welded (W), weld + age (A) and weld + solution heat treat + age (S), X2021-T8E31 (W), 2024-T81 (W), 2219-T87 (S), 7039-T64 (S) and 7106-T6 (A) (S). The most susceptible to stress corrosion cracking was X2021-T8E31 (W). A fatigue crack at the edge of the weld bead caused in­creased susceptibility to stress corrosion for several of the sheet alloy-weld­-tempers. For unnotched plate product, stress corrosion cracking was in­curred for only 2014-T6 (S) and 7039-T64 (S) below 75-percent yield strength; this was at higher stress levels than the (W) and (A) tempers tested. A fatigue crack at the edge of the weld bead caused severe susceptibility to stress corrosion cracking for plate alloys, X2021-T8E31 (S), 7039-T64 (S) and 2014-T6 (S). An Engineering Data Materials Matrix is presented. 5tress corrosion cracking typically initiated at the edge of the weld bead and prog­ressed along the fusion line, branching into the weld bead and heat affected zone. Progression was characterized by a series of jumps exhibiting both corrosion and stress corrosion stages. Additional work is recommended in spectrum loading and natural environment stress corrosion testing, electron beam welding and basic studies of microstructural effects.


Provenance:
Lockheed Martin Missiles & Fire Control
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