Study on the Heterogeneous Nucleation Mechanism of SiC_p/AZ91 Magnesium Matrix Composites under Pulse Current

SiC_p/AZ91D magnesium matrix composites with 30% SiC_p were successfully prepared by pulsed current melting in this work. Then, the influences of the pulse current on the microstructure, phase composition, and heterogeneous nucleation of the experimental materials were analyzed in detail. The results show that the grain size of both the solidification matrix structure and SiC reinforcement are refined by pulse current treatment, and the refining effect is gradually more obvious with an increase in the pulse current peak value. Moreover, the pulse current reduces the chemical potential of the reaction between SiC_p and Mg matrix, thus promoting the reaction between SiC_p and the alloy melt and stimulating the formation of Al₄C₃ along the grain boundaries. Furthermore, Al₄C₃ and MgO, as heterogeneous nucleation substrates, can induce heterogeneous nucleation and refine the solidification matrix structure. Finally, when increasing the peak value of the pulse current, the repulsive force between the particles increases while the agglomeration phenomenon is suppressed, which results in the dispersed distribution of SiC reinforcements.