Research On Novel Complex Modification Of Hypereutectic Al-Si Alloy

As an important cast alloy,hypereutectic Al-Si alloy has low expansion coefficient and density,good cast performance and high wear resistance.However,with the increasing of silicon content,a large number of coarse and irregular lumps primary silicon and needle-like eutectic silicon can be observed,which seriously decreases the comprehensive performance of the alloy.Therefore,primary silicon must be refined to achieve fine dispersive Si phase with desirable properties.In this paper,the effects on microstructure of primary Si and eutectic Si in hypereutectic Al-24 Si alloy under the condition of different modifications were studied,a novel complex modification was got.Microstructure was examined using SEM,XRD and OM.The results showed as follows: The best process data of ZnS modification synthesized by Zn and S was that,modifying temperature 830 oC,content of modification 0.1%,pouring temperature 770 oC.Under this condition,Al-24 Si alloy got the best modification with the size of primary Si decreasing from110 μm to 28 μm.According to study on different method synthesizing ZnS particle with different size,some results were got out.ZnS particle with size of 200 nm was the most effective to modify primary Si,when the content of micron-nano-sized ZnS was only 0.05%,the size of primary was decreased to 22 μm.Furthermore,research on complex modification,we got this conclusion: When adding 0.05% micron-nano-sized ZnS and 0.01% Sr to Al-24 Si melt,complex modification was the best,edges of primary Si was passivated,the size was down to about 25 μm.Moreover,the eutectic Si was changed from needle-plate to granules or grains.The hardness of Al-24 Si alloy was improved by modification,and when the effect of modification better,the properties better.