Evolution of microstructure and mechanical properties of as-cast Al-50Si alloy due to heat treatment and P modifier content.

The effects of superheat temperature, content of modifier (P) and T6 heat treatment on the microstructure and mechanical properties of the Al–50Si alloy have been investigated systematically by scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The results indicate that the primary Si exhibits a plate-like morphology, with average size decreasing with increasing of the superheat temperature for the unmodified alloy. The morphology of primary Si changes to small blocky shape at an optimal P content of 0.5 wt.%, and the nucleation temperature increases for the alloy with 1.3 wt.% P because of the ease of formation of the AlP phase. The nucleation temperature is lower for 0.5 wt.% P due to lack of P atoms at relatively higher temperature. The ultimate tensile strength was enhanced by the addition of P followed by the T6 heat treatment, and the maximum ultimate tensile strength (∼160 MPa) was observed for the sample containing 0.5 wt.% P. [ABSTRACT FROM AUTHOR]