Fatigue Study of Quenched Al-6.5 at % Zn Alloy.
Summary rept. 1 Jul 70-31 Jan 71,
RUTGERS - THE STATE UNIV NEW BRUNSWICK N J MATERIALS RESEARCH LAB
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The defect structure of an Al-6.5 at Zn alloy induced by quenching and low-temperature aging -80 to 60C and the effects of fatigue cycling were investigated. The defect structure upon quenching consisted of homogeneously nucleated dislocation loops, helical dislocations developed from screw dislocations, the latter being introduced by two different processes. The defect structure also contained perfect loops converted from helical dislocations and faulted dislocation loops whose nucleation was enhanced by vacancies generated by quench deformation. Based on experimental evidence, a model is presented explaining the formation of a row of perfect dislocation loops from a single helical dislocation. The interrelation of the various types of induced defects is shown by correlating their formation with the aid of vacancy mechanisms. The absence of a delineated cell structure in the fatigue-cycled specimens and the homogeneous distribution of the dislocations within the grain were attributed to the barrier effect of the quench-induced dislocation loops pinned by precipitates. This barrier effect also gave rise to a large accumulation of dislocations at grain boundaries induced by cycling. The accumulation of dislocations at the grain boundaries appeared to provide the driving force for fatigue-induced boundary migration. The latter facilitated precipitation of zinc-rich particles at the boundaries. Author
- Properties of Metals and Alloys