A Study on the Hot Deformation Behaviors and Structural changes of Aluminum Alloy

Changes in flow stress and deformation microstructure of 7075 aluminum alloy was studied in compression at 753 K and at constant true strain rates from 5.4×10-6 to 2.2×10-1 s-1. The flow characteristics were classified into three types and analyzed in each region of testing conditions, as L, M, and H. The strain rate dependence of yield stress σy is changed at two deformation conditions at which σy is around 15 and 30 MPa, and that of steady state flow stress σss at a condition where σss is around 15 MPa. The flow characteristics are finally classified into three types and analyzed in each region of test conditions, as follows; L, M and H. The relationship between such flow characteristics and new fine grain structures were analyzed in detail and the mechanisms of hot deformation and work softening in regions L and M were discussed. The deformation equation for σy or σss can be approximated by a power law, which is different in each region. In region L where flow stresses are below 15 MPa, extensive work softening occurs more clearly and approaches about 0.75 to peak stress. In region L, the elongated and thin grains seen in L-ST plane are folded and inclined with straining, leading to the formation of new fine grains. It is concluded that the work softening in region L results from the grain refinement evolved by deformation and the operation of grain boundary sliding.