Successfully achieved extrusion at a hybrid (SiCp-Cf)/AZ91 composite with a 50 % volume fraction

Abstract

A hybrid (SiC_p-C_f)/AZ91 composite with a 50 vol% has been prepared by melt infiltration for the first time. Uniform distribution of SiC_p and C_f was observed in the as-cast composite. The thermal deformation behavior of the hybrid (SiC_p-C_f)/AZ91 composites with the high volume fraction was firstly studied based on the true flow stress-strain curve and the evolution of the thermal processing map. The increase in temperature and reduction in strain rate led to lower stress values on the true stress-strain curve. Furthermore, as the strain increased, the area of the instability zone in the thermal processing map gradually diminished, and the activation energy decreased. Calculations and simulations identified the workability region of the composite material as 680–773 K and 0.003 to 0.1 s⁻¹. Based on these findings, hot extrusion of high volume fraction magnesium matrix composite was successfully initiated for the first time. During extrusion, fracture and directional alignment of C_f along the extrusion path enhanced the flow of the matrix alloy AZ91 and SiC_p, thereby facilitating deformation. Compared to the as-cast composite, the extruded composite exhibited reduced porosity and enhanced mechanical properties, with ultimate tensile strength and elastic modulus reaching 370 MPa and 157 GPa, respectively. Additionally, the thermal expansion coefficient of the extruded composite was approximately 50 % lower than that of the AZ91 alloy. The composites also demonstrated superior high-temperature thermal stability between 300 °C and 400 °C.