Work hardening and softening behavior of Mg-Zn-Ca alloy influenced by deformable Ti particles

Pure titanium particles reinforced Mg-6Zn-0.2Ca magnesium matrix composites were fabricated by semi-solid stirring casting followed by hot extrusion in this work. The microstructures and mechanical properties of the Mg-6Zn-0.2Ca alloy and its composites were studied. The Ti particles in as-extruded composites are significantly elongated along the extrusion direction. The average aspect ratio of Ti particles increases while the average size decreases, with the extrusion temperature decreasing. Ti particles promote the dynamic recrystallization of the matrix alloy, break the long-strip Ca2Mg6Zn3 phases and refine the size of MgZn2 phases in the Mg-6Zn-0.2Ca matrix, especially for low extrusion temperatures. The Ti-p/Mg-6Zn-0.2Ca composite extruded at 240 degrees C exhibited a high yield strength (YS) of 383.6 MPa with an ultimate tensile strength (UTS) of 404.8 MPa and a decent elongation to failure (EL) of 4.8%. The high strength is associated with fine grains, nano-precipitates as well as Ti particles. In addition, the work hardening rate of Ti-p/Mg-6Zn-0.2Ca composite is higher than that of Mg-6Zn-0.2Ca alloy at the early stage of plastic deformation due to the combined effects of the elongated Ti particles, the grain refinement and nano-scale MgZn2 precipitates. However, the work hardening rate of the composite decreases faster owing to dislocations cross-slip. And the composite is easier to soften, which results from grain boundary sliding of fine grains and work hardening of deformable Ti particles.