Microstructure and mechanical properties of ultra-high strength TiC_p/Mg-1.4Zn-2.6Ca-0.5Mn nanocomposite after hot extrusion

A uniform distribution of TiC_p nanoparticles was realized in the TiC_p/Mg-1.4Zn-2.6Ca-0.5Mn nanocomposite fabricated by the method of ultrasonic-assisted semisolid stirring. Microstructure and mechanical properties of the nanocomposite before and after extrusion were investigated. The results show that the grains in the dense area of the second phase were smaller than those in the barren area, and the second phase was Ca₂Mg₆Zn₃. Dynamic recrystallization (DRX) occurred in the nanocomposites after extrusion at different temperatures (350 °C, 310 °C and 270 °C). Both the sizes and volume fraction of DRX grains and precipitates size were obviously refined as the extrusion temperature decreased, while the volume fraction of precipitates increased. Ultrafine recrystallized grain structure (≈0.34 μm) with a substantial of fine precipitates appeared in the nanocomposite extruded at 270 °C. The refined grain structure was not only due to DRX, but also the synergistic pinning effect of nano-TiC_p, precipitated MgZn₂ and α-Mn particles. The optimum tensile strength was achieved in the nanocomposites extruded at 270 °C/0.1 mm•s^–1, and the yield strength (YS), ultimate tensile strength (UTS) and elongation to failure (EL)were ≈439.7 MPa、≈460.2 MPa and ≈1.73%, respectively. The grain refinement strengthening with the contribution ratio over 60% to YS increment was much higher relative to thermal expansion effect, Orowan strengthening and dislocation strengthening.