1990 Volume 40 Issue 5 Pages 369-376
Hot deformation of 7075 aluminum alloy was studied in compression in the temperature range of 723K to 803K and at constant true strain rates from 5.4×10-6s-1 to 0.78s-1. The flow characteristics were classified into three types and analysed in every region of testing conditions, as follows; L, M, and H. In the region H where flow stress was over 30MPa, high temperature yield point phenomenon appeared. Yield stress and steady state flow stress showed almost the same dependence on strain rate. These suggest that the flow in H can be controlled by the dragging motion of dislocations. In the region M where flow stress was between 15MPa and 30MPa, flow softening took place clearly at high strains with increasing temperature or decreasing strain rate. The stress of 30MPa was equal to the Orowan stress resulted from the dispersion of insoluble compound particles. In the region L where flow stress was below 15MPa, flow softening mentioned above occurred more clearly and flow stress depended sensitively on grain size. These suggest that grain boundary sliding takes place frequently during deformation. It is concluded that the flow softening in the regions of L and M results from the apparent grain refinement based on the buckling of pan-caked grain structure and grain boundary sliding.
