Abstract:The effects of different cooling conditions on the mechanical properties and microstructures of a Sr-modified A356 (Al-7Si-0.3Mg) aluminum casting alloy were comparatively investigated using three moulding sands including quartz, alumina and chromite into multi-step blocks. The results show that the mechanical properties and microstructures using chromite sand are the  best. As the cooling speed increases, the dendrite arm spacing (DAS) decreases significantly and the mechanical properties are improved, and the elongation is more sensitive to the cooling speed as compared with the tensile strength. The increase of the properties is primarily attributed to the decrease of the DAS and the increase of the free strontium atoms in the matrix. In particular, the regression models for predicting both the tensile strength and the elongation for Sr-modified A356 aluminum casting alloy were established based on the experimental data.

Key words: A356 aluminum alloy; sand casting; cooling condition; strontium modification; microstructure; mechanical properties