Utilizing a novel modifier to realize multi-refinement and optimized heat treatment of A356 alloy

Abstract

Al-5Sr-8Ce master alloy was fabricated as a novel modifier, and its effect on the microstructure and tensile properties of A356 alloy was systematically investigated. The solution treatment time was also optimized based on the modification efficiency of Al-5Sr-8Ce. Results showed that Al-5Sr-8Ce mainly comprised α-Al, Al4Sr, and Al11Ce3 phases. With increasing addition of Al-5Sr-8Ce to 0.4 wt%, both the grain size and secondary dendrite arm space (SDAS) were significantly refined, while the eutectic Si morphology was modified from plate-like to small granular and rod-like morphologies. Grain growth inhibition caused by Ce segregation and the formation of Ce containing intermetallic compounds along the grain boundary was mainly responsible for the grain refinement. The excellent modification effect was attributed to the enhanced Sr modification and the inhibited growth of eutectic Si under the action of Ce. The multi-refinement of microstructure by Al-5Sr-8Ce improved the tensile properties of alloy, in particular a significant increase in elongation. However, the excess addition of Al-5Sr-8Ce (>0.4 wt%) increased the formation of coarse Ce containing intermetallic compounds, deteriorating the ultimate strength and elongation of the modified alloy. Based on the excellent Si modification by adding 0.4 wt% Al-5Sr-8Ce, the solution treatment time was successfully shortened to 90 min.