Effect of Heat-Treatment on Microstructure and Mechanical Properties of Sonicated Multicomponent AlMgSiCuZn Alloy

In this study, an AlMg₈Si₉Cu₁₀Zn₁₀ (in wt%) alloy is fabricated with a high volume fraction of coarse secondary phases, which is higher fraction than in the conventional piston alloys. Ingots are cast in a permanent mold after an ultrasonic melt treatment for 60 s at the temperature range of 750–700 °C. Microstructure of AlMgSiCuZn alloy consists of Si, Zn, Mg₂Si, Q-Al₅Cu₂Mg₈Si₆, and θ-Al₂Cu phases. By the heat-treatment at 440 °C, Q-phase at the vicinity of blocky Mg₂Si phase grows and the roundness of the second phases increases with respect to the heat-treating time. Compared with the as-cast specimen, room-temperature ultimate compressive strength of the heat-treated specimens increases. However, maximum compressive stress at 350 °C is slightly decreased by heat treatment. The formation of fine clusters increases the ultimate compressive strength, while the spheroidization of bulky secondary phases during heat treatment deteriorates the ultimate compressive strengths.