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STUDY OF STRESS-CORROSION CRACKING OF ALUMINUM ALLOYS
Final rept. 6 Apr 1966-5 Apr 1967
ROCKETDYNE CANOGA PARK CA RESEARCH DIV
Pagination or Media Count:
A further clarification of the mechanism of stress-corrosion cracking in 7075 aluminum alloy was obtained, particularly with regard to the role of dislocations in the mechanism and to the relationship between dislocation mobility and susceptibility to stress-corrosion cracking high dislocation mobility reduces susceptibility. It was demonstrated during stress-corrosion tests on 7075-T73 specimens that had undergone prior plastic deformation, that the introduction of dislocations alone did not lower the dislocation mobility sufficiently to diminish the stress-corrosion resistance. This is in contrast to similar experiments with -T6 specimens, wherein precipitation was induced by similar deformation and the mobility was reduced sufficiently to lower the stress-corrosion resistance. An important role for immobilized dislocations was also suggested by a theoretical calculation of the stress field around an edge dislocation which neighbors a grain boundary precipitate. This calculation, which was based only on elasticity theory and thus precluded plastic flow, indicated that a large tensile stress, theoretically as high as 250,000 psi, could act normal to the precipitate-matrix interface. When the capacity for plastic flow i.e., the dislocation mobility was intentionally reduced by notching a stress-corrosion specimen, a rapid failure could be induced in normally resistant 7075-T73 alloy.
APPROVED FOR PUBLIC RELEASE