中文摘要：

本文以直流四电极法探索了Al-18%Si合金在升温过程中熔体的电阻率-温度（-ρT）关系,根据在800~950℃及950~1050℃区间-ρT的异常行为分析认为,后者对应液-液结构转变,其间原先的Si原子团簇被打破,原子重新排列形成新的细小团簇,液体结构更加均匀,而前者则为预转变。依据上述信息采取不同温度分别进行熔体过热处理来探索其凝固组织的差别,结果发现,相对于常规熔炼温度,在高于熔体结构转变温度（1150℃）进行熔体过热处理,初晶硅明显细化,而在预转变状态进行熔体过热处理并不能明显改变凝固行为和组织。

英文摘要：

By means of the d.c.four-probe technique,the relation between electrical resistivity of Al-18%Si alloy and the temperature（ρ-T）was explored during the heating process.By anomaly behavior analysis on ρ-T within the temperature ranges of 800 ℃~950 ℃ and 950 ℃~1050 ℃,we found that liquid-liquid structure transition happened during 950 ℃~1050 ℃,in which the original Si clusters were broken and atoms rearranged to form new small clusters with more even-distributed liquid structure while a structure pre-transition happened during 800 ℃-950 ℃.According to the above information,melt overheating treatments were carried out under different temperatures to search for the disparity between solidification structures.The results show that the treatment under 1150 ℃ after the melt structure transition distinctly refines primary silicon relative to conventional melting temperature.However,that treatment in the pre-transition state can not significantly alter the solidification behavior and structure.