Effect of SiCp on the solidification process of magnesium

Abstract

In this paper, SiCp was added to the pure Mg matrix by ultrasound-assisted stir casting to prepare SiCp-reinforced magnesium matrix composites. The solidification process and solidification structure were analyzed. The results show that SiCp reacts with a pure magnesium matrix to form the element Si, which affects the nucleation temperature and phase transition time of alloys. The presence of Si element decreases the nucleation temperature of α-Mg. As the SiCp content increases, more Si elements are present, which leads to a lower nucleation temperature of α-Mg. In addition, elemental Si and Mg undergo a eutectic reaction to form Mg2Si, which prolongs the phase transition. Elemental Si also affects the solidification process of Mg. During solidification, the element Si generated by the reaction is enriched at the front of the solid-liquid interface, leading to compositional undercooling, which results in the growth of α-Mg through a non-flat interface. When the α-Mg solidification is complete, a solid solution rich in Si elements is formed. Subsequently, the Si element precipitates from the α-Mg solid solution by secondary crystallization as Mg2Si distributed at grain boundaries and inside the grains.