The Research Of Refinement On Primary Silicon In Hypereutectic Al-Si Alloy

As an important cast alloy, hypereutectic Al-Si alloy has low expansion coefficient and density, good cast performance and wear resistance. With the increase of silicon content, the alloy has a further decrease of linear expansion coefficient but further increase of wear resistance and heat resistance. However, the increased silicon content alloy has a large number of coarse and irregular lumps primary silicon and needle-like eutectic silicon, which seriously decrease the comprehensive performance of the alloy. So, refining its microstructure is a necessary way of improving comprehensive performance of the alloy.In this paper, the modification effect of hypereutectic Al-24Si alloy on was studied. The morphology and the size of primary Si was modified by a new refiner-ZnS in hypereutectic Al-Si alloy. The effect time of refiner and the influence of heat treatment that was studied. Microstructure of hypereutectic Al-Si alloy without and with refinement were examined using scanning electron microscope(SEM), X-ray diffraction(XRD) and Energy-dispersive X-ray spectroscopy(EDS). The hardness of hypereutectic Al-24Si alloy can be obtained. The results show that with ZnS refinement, the size of primary Si particles decreased significantly. With increase of ZnS content, these petals-like primary Si particles were disappeared and the number of coarse-flake-like reduced, and the size decreased and then increased, hardness was the opposite. When the amount of ZnS is 0.15 percent, the the smallest size of the primary Si was obtained, and the size of primary Si can be refined from 132 μm to 30 μm. Different time of modification has been studied.30 minutes was the best time and it was not beyond 120 minutes. Heat treatment was carried out for hypereutectic Al-Si alloy with refinement, the morphology of primary Si has changed round.