High strength TiCp/Mg-Zn-Ca magnesium matrix nanocomposites with improved formability at low temperature

Abstract

A novel TiCp/Mg-4Zn-0.5Ca nanocomposite was successfully developed by using the ultrasonic-assisted semisolid stirring method, and then extruded at the speed of 0.01 mm/s with low extrusion temperatures of 270, 230 and 190 °C, respectively. The experimental results indicated that ultrasonic-assisted semisolid stirring could be able to realize the uniform distribution of nano-sized TiCp in the nanocomposite. The external addition of TiC nanoparticles refined the grain dimension of the matrix alloy and improved the morphology of eutectic Ca2Mg6Zn3 phases. The particle stimulated nucleation caused by TiCp provided large driving force for the dynamic recrystallization at the low temperature of 190 °C, leading to high volume fraction of recrystallized grains and formability of TiCp/Mg-4Zn-0.5Ca nanocomposite. The smallest grain size of ∼0.34 μm obtained at 190 °C was caused by two factors, one was due to the temperature reduction, the other was attributed to the coordination pinning effect of nano-scale TiC particles with MgZn2 precipitates. The elongation of the present nanocomposite extruded at 270 °C was improved by 158.2% than the level in as-extruded matrix alloy. This could be ascribed to that the addition of TiC nanoparticles could act as nucleation sites for the recrystallization, and thus coordinate the deformation of matrix. The tensile strength increased as the extrusion temperature decreased, YS of ∼355.3 MPa, UTS of ∼385.7 MPa and EL ∼10.2% were obtained for the TiCp/Mg-4Zn-0.5Ca nanocomposite extruded at 190 °C. The excellent mechanical properties were associated with combining effects of the addition of TiC nanoparticles, grain refinement and a large amount of precipitated MgZn2 phases.