Investigation on the movement mechanism of reinforcements during the melt static holding of SiCp-Cf/Al matrix composites

The distribution of reinforcements in the melt is a key factor influencing the preparation of high-performance aluminium matrix composites by stir casting. The movement behaviour mechanism of hybrid reinforcements in melt remains unclear due to the significant density differences between silicon carbide, carbon fiber, and the Al matrix, hindering the fabrication of high-performance hybrid reinforced Al matrix composites. Therefore, this paper employs the stirred casting method to prepare a SiC _p-C _f/Al matrix composite melt. The effects of different reinforcement additions, melt static holding temperatures, and vacuum environments on the reinforcement movement behaviour were investigated. The results indicate that under atmospheric conditions, both SiC particles and carbon fibers exhibit upward flotation in the melt. An increase in the amount of reinforcement leads to a higher collision frequency and greater frictional resistance during particle movement, thereby slowing the flotation of the hybrid reinforcement. Increasing the static holding temperature enhances the Brownian motion of the reinforcements and reduces the melt viscosity, thereby decreasing the constraints on reinforcement movement and accelerating the flotation of the hybrid reinforcement. Vacuum-assisted stir casting demonstrates that reducing gas entrapment effectively mitigates the flotation of reinforcements. The reinforcement surfaces are wrapped by a micro-bubble layer, resulting in a combined density of the reinforcement and bubble layer that is lower than that of the melt, thereby causing the upward flotation of reinforcements. This study provides theoretical guidance for the preparation of novel hybrid reinforced Al matrix composites.