熔体预结晶状态对Al-20% Si合金中初生Si相的影响

Influences of melt pre-freezing characteristic on primary Si phase of hypereutectic Al-20% Si alloy

通过将Al-30%Si高温熔体与已开始结晶的Al-10%Si熔体相混合,并在不同过热条件下凝固,研究过共晶Al-20%Si熔体的预结晶状态对合金凝固组织的影响.结果表明:改变了合金预结晶状态的混合熔体可以获得分布均匀、尺寸小于40μm的初生Si,且过热处理可以进一步细化初生Si相.分析表明,将900℃的Al-30%Si熔体与580℃的Al-10%Si熔体混合可使Al-20%Si混合熔体的温度大幅降低至670℃,远低于两熔体混合前温度的平均值740℃,从而增大了合金液在凝固时的过冷度,细化初生Si相.过热混合熔体时,由于熔体微区仍存在成分和温度的不均匀性,使初生Si尺寸进一步减小.

By the way of mixing the high temperature hypereutectic Al-30%Si alloy melt with the pre-crystallized low temperature hypoeutectic Al-10%Si alloy melt,then superheating the mixing melt,the effect of melt pre-freezing characteristic on microstructure of Al-20%Si alloy was investigated.The results show that,the primary Si granules of the sample poured by melt mixing with different composition and temperature are well distributed,in which sizes of granules are less than 40μm.When superheated,the primary Si phase can be further refined.Analysis suggests that,the melt mixing treatment can significantly reduce the temperature of the mixing melt to 670 ℃ which much lower than the mean temperature 740 ℃ when mixed the high temperature 900 ℃ of Al-30%Si and low temperature 580 ℃ of Al-10%Si,and increase the degree of undercooling,which leads to the refinement of primary Si.During the superheating treatment,the growth,local melt,and proliferation of primary Si occurs because of the inhomogeneous microdistribution of temperature and composition within the mixing melt,making the further decrease of primary Si size.