Site effectiveness of thin-wall aluminum-silicon alloy castings in differential pressure casting process

Different site microstructure and mechanical properties of aluminum-silicon alloy in differential pressure casting process were investigated. The gate system was adopted vertical slitting gate system. In the investigation at the inner-gate site of the castings the grain is finer, the density is higher and the mechanical properties is best than that of at the cooling site of castings no matter with SiO₂ sand mould, SiC sand mould or chill. However, the grain size, density and mechanical properties of castings between inner-gate site and cooling site are minimum. The analysis results reveal that solidification pressure has site effectiveness during producing aluminum alloy castings by using vertical slitting gate system with a differential pressure casting process. At the inner-gate site the molten metal has higher temperature and longer solidification time that makes solidification pressure has longer performance time during molten metal solidification process. Thus solidification pressure has prominent effect on solidification of molten metal at inner-gate site. At the cooling site of the casting the molten metal has the lowest temperature and the shortest solidification time. The solidification pressure has little effect on the solidification of the molten metal at this site. By contraries, the cooling rate has prominent effect on grain size, density and mechanical properties. The solidification of molten metal between the inner-gate site and the cooling site of casting receives little effect from solidification pressure and cooling rate and give rise to biggest grain size, minimal density and lowest mechanical properties. With the increase of cooling rate, the microstructure and properties of castings at every site are improved.