The microstructures of Al-20%Si (mass fraction) alloy prepared by melt thermal treatment (including the melt mixing and melt superheating) were studied combining with chemical metamorphism to further refine the primary silicon. The results show that, when the mixed melt is superheated to 900 ℃, the grain size of primary silicon is decreased to about 34 um. And adding the modificator or refiner into the melt before melt mixing can further refine the primary silicon of Al-20%Si. Especially, when the Al-10%Si melt mixes with the Al-30%Si melt added 0.2%Al-5Ti-C-3Ce and 0.4%Cu-10P, respectively, then superheated the mixed melt, the primary silicon of Al-20%Si is well uniformly distributed in tiny blocklike with the grain size less than 10 μm, which makes the matrix of the alloy exhibit typical composite characteristic. The analysis shows that the melt thermal treatment and adding modificator or refiner at the same time have multiple modification effects on the primary silicon. The melt thermal treatment increases the supercooling degree during the solidification process of the alloys to refine or modify the primary silicon because of the re-melt of primary α(Al) and the recombination of chemical bond in Al-Si alloy as mixing the different melt together. And then superheating the mixing melt can make the pre-ciystallized primary silicon split and proliferate, thus further refine or modify the primary silicon. And adding refiner or modificator can improve the refinement effect of the melt thermal treatment on the primary silicon of the Al-Si alloys.%采用熔体温度处理(包括熔体混合及过热处理)工艺研究Al-20％Si(质量分数)合金凝固组织,并结合化学变质法进一步细化初生硅相.结果表明,当熔体经混合后过热至900℃时,初生硅的尺寸约为34 μm;添加变质剂后再进行熔体混合可以使Al-20％Si中的初生硅相进一步细化,特别是在Al-10％Si和Al-30％Si 中分别 添加0.2％Al-5Ti-C-3Ce和0.4％Cu-10％P后,再进行熔体过热处理,合金中的初生硅呈小块状弥散分布,且尺寸在10μm以下,材料基体呈现出典型的复合材料特征.熔体温度处理与添加化学变质剂方法对初生硅相有显著的多重变质细化作用；在熔体混合时α(Al)的重新熔化和熔体化学键的重组,增大了合金液在凝固时的过冷度,使初生硅相得到细化；对混合熔体再进行过热处理时,混合熔体中的Si相发生熔断、增殖,从而使合金中初生硅相得到进一步细化.添加细化剂或变质剂会明显增强熔体温度处理对Al-Si合金中初生硅的细化效果.
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