Microstructure, texture and mechanical properties of Mg-2.10Zn-0.58Ca-1.02Zr-10.34SiCp (wt%) composites after being extruded at different speeds

Abstract

The Mg-2.10Zn-0.58Ca-1.02Zr-10.34SiC_p (wt%, SiC_p/ZX20K) composites were fabricated by stir casting and hot extruded at 400 °C with extrusion speed of 5 mm/s and 10 mm/s, respectively. The SiC particles, which initially exhibited a necklace-type distribution at the grain boundaries, transformed into a band-type distribution after hot extrusion. The SiC_p/ZX20K composites underwent complete recrystallization, resulting in a pronounced bimodal microstructure consisting of coarse secondary recrystallized grains in the SiC-poor region and fine grains in the SiC-rich regions. A basal plane fiber texture was achieved, with the {0001} plane oriented parallel to the transverse direction (TD). Moreover, grains with their <2-1-10> orientation parallel to the extrusion direction (ED) experienced preferred growth because those grains possessed characteristics such as larger initial size, lower storage energy, and a larger orientation difference from neighboring grains. The SiC_p/ZX20K composites extruded at 5 mm/s exhibited a yield strength (YS) of 218 MPa, with a decent elongation to failure (EL) of 4.8% and an ultimate tensile strength (UTS) of 294 MPa which was 2.3 times greater than that of the as-cast state. Increasing the extrusion speed resulted in better overall mechanical properties and reduced the anisotropy in mechanical properties, due to the combined effects of texture, particle orientation and particle distribution.