Study On The Solidification Shrinkage Of Hypereutectic Al-Si Alloys

Study on the solidification shrinkage of hypereutectic Al-Si alloys can provide a reference for reasonable casting process design. Based on Archimedes’ Principle, the density of hypereutectic Al-Si alloys with different Si contents and under different melt heat treatments are researched by measuring the buoyancy of Al-Si alloys immersed in molten salt. The solidification shrinkage rates, the liquid molar volumes of Al-Si alloys and the partial molar volumes of aluminum in Al-Si alloy melts are determined and the effects of Si content on them are researched. The influences of melt temperature and holding time on the precipitation rate of primary silicon during solidification process and solidification shrinkage are researched. The main conclusion can be drawn as follows.(1) The density of hypereutectic Al-Si alloys at their liquidus temperature and eutectic temperature varies with Si content. When the silicon content is between 12.6% and 30%, the density of Al-Si alloy at liquidus temperature increases while the density of the solidified Al-Si alloy decreases with increasing silicon content. The solidification shrinkage rate of Al-Si alloy decreases with the increase of silicon content. When the silicon content is 25%, the solidification shrinkage of Al-Si alloy is close to 0. The volume of Al-Si alloy after solidification is larger than that before solidification when the silicon content is higher than 25%.(2) When the silicon content is lower than 25%, with the increase of silicon content, the molar volumes of hypereutectic Al-Si alloys at liquidus temperature and 754℃ decrease while the partial molar volume of Al in Al-Si alloy melts increases. When the silicon content of Al-Si alloy is in the region between 25% and 30%, the molar volumes of Al-Si alloy liquids at liquidus temperature and 754℃ increase with increasing silicon content.(3) When the superheat degree of Al-24.2%Si alloy melt is lower than 200 ℃, the solidification shrinkage decreases with increasing the superheat degree and the holding time. When the superheat degree of Al-24.2%Si alloy melt is higher than 200 ℃, the solidification shrinkage increases with increasing the superheat degree.