Changes in Grain Size, Texture, and Mechanical Properties of AZ31/(TiO2)p Nanocomposites Processed by Isothermal Multidirectional Forging

In the current study, magnesium-matrix AZ31/ 1.5 vol.% (TiO2)p nanocomposites manufactured using stir casting underwent extrusion process. The as-cast ingots were extruded, then processed by multidirectional forging (MDF) up to 8 passes at constant temperature of 320◦C. Investigating microstructures showed that after the second pass, the size of matrix grains underwent a significant decrease. However, this decrease didn’t continue in subsequent passes and grain size increased at the fourth pass. In the sixth pass, grain size decreased again, resulting in the smallest microstructure in all the samples. However, in the last two passes, grain size increased similar to the case of the fourth pass. The results of shear punch and Vickers’ microhardness tests showed that changes in shear yield strength, ultimate shear strength, and hardness followed a similar trend. Furthermore, the results of these tests showed that the best mechanical properties are observed in the first two passes after which no further improvement is observed in shear strength and hardness of the samples while fourth, sixth, and eighth passes resulted in better mechanical properties compared to the extruded sample.