A study of intermetallic phase stability in Al-Si-Mg casting alloy: The role of Cu additions

The influence of Cu content (0, 0.5 and 1 wt%) on the nature of intermetallic phases was carefully investigated in a AlSiMg casting alloy. Four different Cu-bearing phases, with a Cu content ranging from 5% to 30%, were identified by Energy Dispersive Spectroscopy. The Al-Mg-Si-Cu quaternary phase was found coupled to Si particles and the Ө-Al2Cu to brittle β-Al5SiFe phase. Copper modified the stability and the dissolution kinetics of iron-bearing intermetallics (π-Al8FeMg3Si6 and β-Al5SiFe) during solution treatments at 773 and 803 K (500 and 530 °C). In 0% Cu and 0.5% Cu samples, (β+ π) area fraction decreases with time, while it remains almost constant and comparable at the end of two solution treatments in 1% Cu samples. Moreover, the Q-Al5Cu2Mg8Si6 and Mg2Si intermetallic area fraction increased with copper (in 0.5 and 1% Cu samples) especially at the highest temperature of investigation (803 K - 530°C) and slightly decreased with time.