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 (similar to 160 MPa) was observed for the sample containing 0.5 wt.% P. (c) 2015 Elsevier Ltd. All rights reserved.