Effects of injection velocity on microstructure, porosity and mechanical properties of a rheo-diecast Al-Zn-Mg-Cu aluminum alloy

A semisolid slurry of Al-Zn-Mg-Cu alloy was prepared by adding 0.1 wt.% Al-5Ti-1 B master alloy and rheo-diecast with different injection velocities. The average size of the primary α-Al particles in the rheo-diecast parts decreased and its shape factor increased with the increase of the injection velocity. The microstructure was obtained with an average particle diameter of 52 μm and a shape factor of 0.69 for the primary α-Al particles at 1.0 m s−1. With increasing injection velocity, porosity decreased to a minimum of 0.9%, at an injection velocity of 0.7 m s−1, and then increased with the increase in injection velocity. At this velocity, the maximum tensile strength and elongation of the rheo-diecast samples were achieved, which were 252 MPa and 2.8%, respectively. After T6 heat treatment, the tensile strength and elongation of the samples were 403 MPa and 2.1%, an increase and decrease of 60% and 25%, respectively, compared to the as-cast samples.