Evolution of the solidification phases and Al3(Er,Zr) particles in a novel Al–Zn–Mg–Cu–Er–Zr alloy during homogenization

The effects of homogenization treatments on evolution of the solidification phases and Al 3 (Er,Zr) particles in a novel Al-Zn-Mg-Cu-Er-Zr alloy have been investigated. Three distinct solidification phases (the low-melting-point eutectic T(AlZnMgCu) phase, Al 8 Cu 4 Er phase and Al 17 (Fe 3.2 Mn 0.8 )Si 2 impurity phase) were observed to segregate at grain boundaries in the as-cast alloy. The mechanism of the dissolution and evolution of the primary phases in as-cast alloy is not completely consistent during the homogenization process, but can essentially be described by three stages: Thinning, Discontinuation, and Full Dissolution (Spheroidization). The precipitation, growth, and coarsening of Al 3 (Er,Zr) particles were investigated at 470 °C under different heating conditions (with heating rates of 25 °C/h and 50 °C/h, designated as HT25 and HT50, respectively) and compared with the conventional homogenization process (without a specified heating rate, designated as HT), all held for varying durations. Compared to the HT process, the HT25 and HT50 treatments gave rise to Al 3 (Er,Zr) particles characterized by a higher number density, a greater volume fraction, and a relatively smaller average size. The Al 3 (Er,Zr) particles in the HT and HT25 samples demonstrated more rapid growth and coarsening kinetics, resulting in larger particle sizes but lower volume fractions and number densities compared to those in the HT50 samples. This disparity is ascribed to the fact that the growth and coarsening mechanisms of Al 3 (Er,Zr) particles are regulated by the diffusion rates of Er and Zr solutes and the interfacial reaction rates at the particle/matrix interface within the alloy.