Microstructural and Mechanical Evolution of Semisolid 7075 Al Alloy Produced by SIMA Process at Various Heat Treatment Parameters

A homogeneous equiaxed grain structure is necessary for semisolid forming of aluminum alloys. One of the methods used to obtain such microstructure is strain induced melt activated process. The aim of this work is to optimize the heat treatment parameters for extruded 7075 alloy required to obtain the spheroidal grain structure suitable for thixoforging. For this purpose, 7075 was subjected to isothermal heat treatment at two different temperatures, 620 and 630 degrees C for 5, 10, 15, 20, 25, 30, 35 and 40 min. Optical microscopy analysis and mechanical tests were carried out to characterize the effects of different isothermal heat treatment parameters. Optimal heat treatment parameters were determined by the change in mechanical properties and microstructure. It was found that at 630 degrees C for 25 min resulted in 564 MPa yield stress, 616 MPa tensile stress and 5.3% elongation as the highest values in the experimental work carried out in this study.