Preparation of Al-7Si-0.5Mg Semi-solid Slurry by GISS and Its Study on Microstructure and Properties

Al-7Si-0.5Mg aluminum alloy semisolid slurry with fine and uniform grain size and good sphericity was prepared by gas induced semi-solid（GISS） process, and the effects of holding time and medium alloy（Al-5Ti-1B） addition in the GISS process parameters on the microstructure of the semisolid slurry were investigated. The results show that with the increase of resting time from 85 s to 271 s, the solid phase fraction of the semisolid slurry increases in the range of 0.67-0.77,the average grain size increases from 95 μm to 226 μm, and the average shape factor decreases from 0.80 to 0.33. When the medium alloy addition varies in the range of 0.5wt%-2.0wt%, a better slurry microstructure was obtained at about 1.5wt%.Compared with the conventional liquid die-casting, the semi-solid die-casting improves the mechanical properties of the tensile bars, and after heat treatment, the tensile strength, yield strength and elongation of the tensile bars reach 307 MPa, 240 MPa and 8.8%, respectively. In conclusion, the GISS process can prepare the semi-solid slurry with uniform and round structure, and the semi-solid die-casting can improve the mechanical properties of Al-7Si-0.5Mg aluminum alloy.