The optimal solution treatment condition in a Al-Si-Cu AC2B alloy

The precipitates, hardness, and tensile properties of Al-6.2Si-2.9Cu AC2B alloy were investigated with respect to solution treatment time at 500°C. Al(Cu)-Al₂Cu eutectic, Si, 0-(Al2Cu), and Q-(Al₅Cu ₂Mg₈Si₆) phases were observed in the as-cast specimen. With increasing the solution treatment time at 500°C, the Al(Cu)-Al₂Cu eutectic and θ-(Al₂Cu) phases were gradually reduced and finally almost disappeared in 5 h. The mechanical properties, such as hardness, tensile strength, and elongation, were improved with solution treatment time until about 5 h due to the dissolution of the Al₂Cu particles. With further holding time, the mechanical properties did not change much. The solution treated specimens for over 5 h at 500°C exhibit almost the same tensile properties even after aging at 250°C for 3.5 h. Accordingly, the optimal solution treatment condition of the Al-Si-Cu AC2B alloy is considered to be 5 h at 500°C.