Influence Of Alloy Elements And Cooling Rate On Solidification Structure Of Hypereutectic Al-Si Alloy

Hypereutectic Al-Si alloy features characteristics of low density, superior hardness, heat resistance, wear resistance and good mechanical properties. Massive primary Si in the hypereutectic Al-Si appears angle shaped and the eutectic Si appears as rough acicular. The stress concentration appears at the angle of the primary Si under external force, resulting in crack formation and limiting practical application severely. On the basis of previous studies, 3.4%Zr, 3.0%Mn, 2.0%V and 1.0%Cr-1.5%Ti alloy elements are added into hypereutectic Al-Si alloy and sand mold, metal mold, water-cooled metal type three different cooling ways are used and the influences of alloy elements and cooling rate on the solidification structure of hypereutectic Al-Si alloy are studied in this paper.Experimental results show that: 3.4%Zr, 3.0%Mn and 2.0%V weaken the modification effect of P of the hypereutectic Al-Si alloy when the melt is cooled by the sand mold, metal mold and water-cooled metal mold. 3.4%Zr, 3.0%Mn and 2.0%V make the number of the primary Si decreases and the size increases.The granular eutectic Si is formed between the primary Si when 3.4%Zr are added into the hypereutectic Al-Si alloy and the granulation is better with the acceleration of the cooling rate. The granular Si phase only can be achieved by adding 3.0%Mn when the melt is cooled by the water-cooled metal mold. 2.0%V can refine the eutectic Si in the hypereutectic Al-Si alloy, but can not cause the granulation of the eutectic Si.3.4%Zr have little effect on the α phase in the hypereutectic Al-Si alloy when the melt is cooled by the sand mold, metal mold and water-cooled metal mold. 3.0% Mn can induce equiaxed α phase precipitates in hypereutectic Al-Si alloy and α phase is refined under different cooling conditions. 2.0%V makes the proportion of α phase in the solidification structure increase in hypereutectic Al-Si alloy when the melt is cooled by the sand mold, metal mold and water-cooled metal mold.The dimension of the primary Si in the solidification structure decreases by 12.24%-51.65% after the composite modification of 1.0%Cr-1.5%Ti for the Al-25%Si alloy when the melt is cooled by the sand mold, metal mold and water-cooled metal mold. Compounds containing Cr formed between the primary Si prevent the aggregation of the primary Si during the solidification process, leading to the increasement of the uniform degree of the distribution of the primary Si. The number of compounds containing Cr and Ti increases as cooling rate increases.