Influences of Fe, Mn and Y additions on microstructure and mechanical properties of hypoeutectic Al-7%Si alloy

In this work, the influences of Fe, Mn and Y with various contents on microstructural evolution and mechanical properties of hypoeutectic Al-7%Si alloy were investigated by microscopy technology and tensile test. The results showed that the complex addition of Al-20%Si-2.5%Fe-2%Mn master alloy and rare earth Y have much better refining effect of need-like eutectic Si and coarse alpha-Al dendrites than that of separate addition of master alloy or rare earth Y. Combined additions of 7.0% master alloy and 0.2% Y, the average grain size was decreased by 89.5% from 483.1 mu m to 50.8 mu m and secondary dendrite arm spacing (SDAS) was reduced by 46.8% from 26.9 mu m to 14.3 mu m. Moreover, the coarse flake-like eutectic Si structure was effectively modified into fine fiber and granular shape. In addition, ultimate tensile strength (UTS) was improved by 33.3% from 162 MPa to 216 MPa, and elongation (El) value was enhanced by 46.7% from 6.2% to 9.1%. The fracture mode transformed from brittle fracture to ductile fracture.