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The mechanism of stress-corrosion cracking in 7079 aluminum alloy was investigated by analysis of microstructural changes that occur during exposure to 3.5 per cent NaCl solution. During the corrosion reaction dislocation networks were generated within the grains and along strain-contour bands. Grain-boundary voids occurred where several of these bands originated or terminated. This suggests that the intragranular structure develops as a result of hydrogen entering the alloy and that the voids are propagated under applied load to form grain-boundary cracks. This study is in the preliminary stages and is being continued. (Author).
The resistance of a 7079-T6 aluminum alloy to stress-corrosion cracking in seawater was examined by testing precracked cantilever beams fabricated of the alloy. Specimens tested in the direction of rolling were found to have gained substantially in notch strength after long-time exposure to the stress-corrosion cracking condition. The results are compared with those obtained by a conventional test method. (Author).
This report deals with the stress-corrosion cracking of aluminum alloys, and it represents an effort by DMIC to expand on the information contained in DMIC Memorandum 202, 'Stress-Corrosion Cracking of Aluminum Alloys', dated February 15, 1965. DMIC Report 228 begins by presenting a comprehensive definition of stress-corrosion cracking. This is followed by sections dealing with (1) the historical development and growth in awareness of the problem, (2) the mechanisms involved, and (3) the theory of stress-corrosion cracking. A section on experimental techniques is presented. These techniques include test methods used to determine the susceptibility of alloys to stress-corrosion cracking, as well as more refined methods of studying the fundamental mechanisms of the problem. Different evaluation methods, applicable to obtaining the different objectives of stress-corrosion testing, are also presented. All of the foregoing serve as background to the sections on stress-corrosion-cracking behavior of aluminum alloys and preventive measures. (Author).
Cathodic protection schemes can greatly extend the useful life of the high strength aluminum alloy 7079, but because of general cathodic wastage at high cathodic currents, cathodic protection cannot produce indefinite immunity to stress corrosion cracking. For long-term applications in sea water requiring this alloy a high-integrity paint system backed up with a galvanic anode system would be indicated for maximum reliability. (Author).
The report summarizes information from selected European papers and lectures that were published or presented between mid 1967 and July 1, 1968. Subjects discussed include: the nature of stress-corrosion, stress-corrosion in AlMg, AlMgZn, and AlMgSi alloys and testing for susceptibility to stress-corrosion cracking. (Author).