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 degrees C and 350 degrees C, respectively.