Grain refining effects of the melt thermal-rate treatment and Al-Ti-B-Y refiner in as-cast Al-9Si-0.5Mg alloy

This paper investigated the effects of melt thermal-rate treatment and Al-3Ti-3B-1Y grain refiner on the microstructure and mechanical properties of hypoeutectic Al-9Si-0.5Mg alloy. The results showed that the grain refining effect of the melt thermal-rate treatment was more remarkable than that of Al-3Ti-3B-1Y grain refiner. After the appropriate melt thermal-rate treatment (MTRT), the microstructure and mechanical properties of alloy were significantly optimized and the α-Al phase changed from dendritic grains to columnar grain. The MTRT technique compound with Al-3Ti-3B-1Y grain refiner could further refine the microstructure. In addition, the change of vacancy concentration induced the morphology change of α-Al phase. The mechanism of the refinement and the toxic effect of Y element were clarified, which provide a reference for developing a new type of Al-Ti-B-RE grain refiner and the melt treatment method.