Effect of SiCp on the microstructure and tensile properties of the Mg–3Y magnesium alloy

Abstract

Magnesium matrix composite is another competitive light metal matrix composite following aluminum matrix composite, with excellent application prospects in the aerospace and automotive fields. In this paper, the Mg - 3Y – xSiCp (x = 0, 1, 3, 5 wt%) composites are fabricated by stir casting with ultrasonic vibration followed by extrusion. The microstructure of the alloys is investigated by means of scanning electron microscopy (SEM) imaging and electron backscatter diffraction (EBSD) techniques. The results reveal that the composites have a finer grain size due to the particle promoted nucleation (PSN) mechanism. When the SiCp content is 3 wt%, the grain size is the smallest (0.76 μm), and the refinement rate is about 16.7%. Moreover, the addition of SiCp can inhibit the transformation from low-angle grain boundaries (LABGs) to high-angle grain boundaries (HABGs), thus hindering the dynamic recrystallization (DRX) of the alloy, which decreases from 55.7% to 15.4%. The reduction in the proportion of recrystallized grains in the composite leads to increasing the maximum intensity of the texture. In addition, the tensile properties and the strengthening mechanism of the alloys are investigated. The results show that the composites have higher ultimate tensile strength (UTS) and yield strength (YS) due to the combination of grain refinement and dislocation strengthening. When the SiCp content is 5 wt%, the UTS (291 MPa) and YS (283 MPa) increase by ∼12.7% and ∼17.1%, respectively, over the matrix alloy. However, the addition of SiCp causes more oxides and holes in the alloys, which leads to a fracture strain (δ) decrease in the composites.