Effect of heat treatment and Fe content on the microstructure and mechanical properties of die-cast Al-Si-Cu alloys

The effect of solution and ageing heat treatment on the microstructure and mechanical properties of the die-cast Al-9wt.% Si-3.5wt.% Cu alloys containing 0.1-1.0wt.% Fe was investigated. The results showed that the dendritic primary alpha-Al phase was varied from 20 to 100 mu m in size and the globular alpha-Al grains were smaller than 10 mu m in size. The Fe-rich intermetallics exhibited coarse compact or star-like shapes with the sizes from 10 to 20 mu m and the fine compact particles at an average size of 0.75 mu m. The solution treatment of the alloys could be achieved in a short period of time, typically 30 min at 510 degrees C, which dissolved the Cu-rich intermetallics into the primary alpha-Al phase and spheroidised the eutectic Si phase. During the subsequent ageing treatment, numerous fine precipitates of theta' and Q' phases were formed to provide effective strengthening to the alpha-Al phase, significantly improving the mechanical properties. Therefore, Fe content in the die-cast Al-Si-Cu alloys needs to be controlled at a low level in order to obtain the improved ductility and strength under solution and aged condition. (C) 2015 Elsevier Ltd. All rights reserved.