Influences of Modification and Heat Treatment on Microstructure and Mechanical Properties of Hypereutectic Al-20%Si Alloy

The hypereutectic Al-20%Si alloys were modified with P-Cu alloys and Al-Re alloys and treated with T6 heat treatment process.The microstructures and mechanical properties were investigated.The results show that the shape of Si particles is improved obviously by the complex modification of P and RE and T6 process.The size of primary Si particles is obviously decreased.The eutectic Si particles are changed to global or short bar shape.The tensile strength,elongation,hardness and impact toughness are improved.Especially when treated with combination of complex modification and T6 heat treatment process,the tensile strength,elongation,hardness and impact toughness increased to 306 MPa、0.48%、166.7 HB and 11.009 8 J/cm2,which is 27%、54.8%、37.3%、17.7% of that unmodified as-cast alloys.It can be explained that the complex modification of Si particles and T6 process increase the strength of matrix and restrain initiation and growth of crack.