Effects of Zr and Sr on microstructure and mechanical properties of cast Al–Si–Cu–Ni–Mg alloy

Al–Si–Cu–Ni–Mg–(Zr, Sr) alloys were prepared by permanent mold gravity casting. The effects of Zr and Sr on the microstructure and mechanical properties of cast Al-12Si-6Cu-1.5Ni-1.3Mg alloy at room temperature and high temperature were investigated systematically using X-ray diffractometer (XRD), ultra-depth-of-field metallographic microscope, scanning electron microscope (SEM), transmission electron microscope (TEM) and electronic universal testing machine. The experimental results show that the size of eutectic Si phase and Al–Cu–Ni phase is decreased with the addition of Zr, and it has little effect on the primary Si phase. The massive primary Si phase of the alloy with 0.1%Zr + 0.04%Sr addition disappears, and the eutectic Si phase changes from acicular to fibrous phase, which has little effect on the size of the Al–Cu–Ni phase. The ultimate tensile strength, yield strength and elongation of the alloy with 0.1%Zr + 0.04%Sr addition at room temperature are 360 MPa, 318 MPa and 4.2%, respectively. The ultimate tensile strength and elongation of the alloy with 0.1%Zr addition at high temperatures are 194 MPa, 4.3%, 117 MPa, 7.5% at 275 °C and 350 °C, respectively.