Evolution of the main intermetallic phases in Al-Si-Cu-Mg casting alloys during solution treatment

The effect of the copper content and the processing route in the solution treatment of four Al-Si-Cu-Mg alloys was studied. The solidus temperature of each alloy was obtained through differential scanning calorimetry (DSC) and compared with Thermo-Calc calculations. This temperature was between 509–510°C in all cases. In consequence, three temperatures were chosen for the solution treatment: 480, 490 and 500°C. An alternative two-step solution treatment finishing at 535°C was also adopted for the alloy with the lowest copper content. Solution times up to 24 h were considered. The dissolution of the intermetallic phases was measured using both, metallographic analysis and from the evolution of the DSC peaks. The results from the two methods were in good agreement. Thermo-Calc calculations helped explaining the changes in volume fraction of the main intermetallic phases observed during the solution treatments.