Effect of mould sand type and casting wall thickness on properties and microstructure of multivariate Al–7·5Si–4Cu alloy

Abstract

The effects of different mould sands and casting wall thicknesses on the properties and microstructures of multivariate Al-7?5Si-4Cu alloy, which was modified by Al-10Sr, RE and Al5Ti-B master alloys, were investigated. The melt was poured into multistep moulds made from three mould sands (quartz, alumina and chromite) to produce specimens for mechanical property testing and metallography. The results demonstrated that the sample with chromite sand exhibited the best mechanical properties owing to its higher cooling rate. Tensile strength and elongation decreased monotonically with increasing wall thickness. No obvious trend of wall thickness on hardness of the alloy was found. When the cooling speed decreased, the grain refinement and transformation effect became weaker, the dendrite arm spacing (DAS) increased obviously and the properties and microstructures became poorer. A series of fitting models was established and used to predict properties of Al-7?5Si-4Cu alloy from the DAS.