Evolution of Solidification Structure of Hypereutectic Al-Si Alloy Under a Novel Low-Voltage Alternating Current Pulse

The effect of a novel low-voltage alternating current pulse（ACP）controlled by transformer and silicon controlled rectifier on the solidification structure of Al-20%Si alloy was investigated.The results indicated that the remarkable segregation of primary Si occurred during the solidification,and even dendrites ofα-Al phase appeared at the center of samples under ACP.The thickness of segregation layer decreased first and then increased with current density increasing from 0 to 300 Acm-2.The primary Si existed with long pole or five petal star-shaped without ACP.However,the morphology of primary Si phases changed to block under ACP,and the sizes of blocky Si decreased obviously with increasing current density from 110 to 300 Acm-2.The formation mechanism of the structure of hypereutectic Al-20%Si alloy was also discussed under ACP.