The study on characteristics of heat treatment of the direct squeeze cast 7075 wrought Al alloy

The 7075 wrought Al alloy (Al–5.7 wt.% Zn–l.7 wt.% Cu–2.6 wt.%Mg) was prepared using the direct squeeze casting process in order to study the characteristics of heat treatment. The micro-structures of squeeze casts applied with 25, 50 and 75 MPa could be free from the defects that occur with non-pressurized (gravity) die cast billets and became more refined and dense than those of non-pressurized casts. The hardness of 7075 alloy aged at 120 and 180°C was increased with increasing applied pressure due to the increase in the nucleation site of intermediate precipitates. The heat resisting property of 7075 Al alloy was improved by squeeze casting because of grain refinement effect. In case of 120°C for 129.6 ks ageing treatment, the wear loss amount of squeeze cast was decreased as compared with non-pressurized casts, because of a high density of precipitates, fine grained structures and uniform distribution of eutectics in the periphery of grain boundary due to a reduction in solidification time.