Microstructure and Tensile Strength of Nano-TiC_p/Mg–Zn–Ca Magnesium Matrix Nanocomposites Processed by Multidirectional Forging

In this work, a Mg–Zn–Ca magnesium matrix nanocomposite containing nano-sized TiC particles was firstly processed by multidirectional forging (MDF). With increasing the forging temperature from 230 to 310 °C for 1 MDF pass or the number of MDF passes at 270 °C, both volume fractions and average sizes of recrystallized grains increased. The average sizes of precipitated MgZn₂ phases increased with the increase in either the initial forging temperature or MDF passes, and the volume fractions gradually decreased with increasing the initial forging temperature or decreasing the MDF passes. With decreasing the initial MDF temperature, thermal expansion mismatch strengthening slightly decreased while fine-grain strengthening and Orowan strengthening gradually increased, resulting in a gradual increased yield strength. The elongation of the present nanocomposite gradually increased from 8.2% after 1 MDF pass to 22.7% after 6 MDF passes, while both yield strength and ultimate tensile strength did not change significantly. This could be ascribed to that although the fine-grain strengthening gradually reduced, there was no significant change in the Orowan strengthening caused by MgZn₂ phases with increasing the number of MDF passes.