The effect of ultrasonic melt treatment on solid solution treatment temperature and/or time for an Al-7Si-2Cu-1Mg alloy

Ultrasonic melt treatment (UST) is known for refining microstructures including intermetallic compound (IMC)s, and it is expected that the microstructural benefits induced by UST may reduce the time and temperature of solid solution treatment (SST). The effect of UST on SST for an Al-7Si-2Cu-1 Mg alloy was investigated in terms of changes of volume fraction of IMCs in connection with the tensile properties. The results show that UST not only refined the constituent phases but also reduced the volume fraction of IMCs in the as-cast microstructure, which promoted dissolution of Cu and Mg rich IMCs during SST, increasing the yield strength of the alloy. In addition, the SST time to achieve maximum strength was shortened by UST. Without UST, the strength was maximised at 520 °C for 8 hours, while with UST the strength was maximised at 2 ~ 4 hours. The dissolution of the constituent phases upon SST was also discussed.