Refinement of primary Si in hypereutectic Al–Si alloy by electromagnetic stirring

The effect of electromagnetic stirring on the morphology of primary Si particles in a hypereutectic aluminum–silicon alloy was investigated in the semi-solid temperature region. It was found that with the stirring current decreasing from 32 to 16 A, the primary Si particles congregated severely, formed large primary Si particles. When the current was less than 12 A, however, the particle distribution became uniform and there was no any particle congregation. The primary Si particles reached a minimum equivalent diameter of 44.8 μm when the stirring current was 8 A. Nevertheless, when the stirring current was less than 8 A, the primary Si particles coarsened again gradually. The congregating of primary Si particles is attributed to the presence of centrifugal force field caused by electromagnetic stirring, which forced the Si particles to move in radial direction, distribute in grade and congregate. The diameter of the Si particles is decided by the cooperation of the congregation effect and refining effect of electromagnetic stirring. The present research shows that a relatively weak electromagnetic stirring is more effective in refining the primary Si particles than a strong electromagnetic stirring.