High-pressure phase transitions and structure of Al-20 at % Si hypereutectic alloy

Phase transformations of an Al-20 at % Si high-silicon hypereutectic alloy have been studied by differential barothermal analysis at temperatures of up to 800A degrees C in argon compressed to 100 MPa. High pressure has been shown to raise the melting point of the alloy by 5A degrees C during heating and to lower the eutectic solidification temperature by 5A degrees C during cooling in comparison with the canonical phase diagram of the Al-Si system. At a temperature of 553A degrees C, heating and cooling lead to silicon dissolution and decomposition of the aluminum-based solid solution, respectively. After high-pressure solidification, the silicon particles in the alloy have a bimodal size distribution. Quantitative porosity characteristics in the alloy after a barothermal scanning cycle are similar to those in the as-prepared alloy. The lattice parameters of the silicon and aluminum remain unchanged. The microhardness of the aluminum matrix of the alloy corresponds to that of pure aluminum.