Xuyue Yang, Hiromi Miura and Taku Sakai
Department of Mechanical and Control Engineering, The University of Electro-Communications, Chofu, Tokyo
Superplasticity of the prior cold- and warm-worked 7075 aluminum alloy, especially the effect of prior cold-rolling on it, was studied in tension at 798 K and at various strain rates from 10-5 s-1 to 10-1 s-1. Continuous dynamic recrystallization takes place during hot deformation, leading to the evolution of fine grained structure. With increasing prior cold-rolling reduction, new finer grains are evolved faster in the unrecrystallzed matrices and their following coarsening is retarded up to higher strains. These are caused by the pancaking of initial grains developed by cold-rolling, which leads to the decrease in the shortest grain diameter. The strain rate dependence of flow stress and total elongation to fracture is affected sensitively by such a grain refinement, which improves the superplastic characteristics in the medium region of strain rate. It is concluded that superplasticity takes place in 7075 aluminum alloy cold- and warm-worked under appropriate conditions and can be controlled mainly by grain boundary sliding.
(Received Fabruary 28, 1996)
superplasticity, 7075 aluminum alloy, cold rolling, continuous dynamic recrystallization, grain boundary sliding
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