Effect of severe plastic deformation by multidirectional forging on mechanical properties of Ti modified SiP/ZA22 composite

In this study, the effect of multidirectional forging (MDF) was studied on the microstructure and mechanical properties of Ti-modified SiP/ZA22 composite containing 4 and 8 wt. % Si. The forging process was performed at 100 °C by two and five passes. Based on the obtained results, Ti modification refined the coarse primary dendrites, and reduced the size of primary Si (SiP) particle as well as grains. Applying MDF also gradually eliminated the dendritic structure, promoted fine distribution of SiP particles, second phases, and porosities in the microstructure. According to the image analysis results, the average size of SiP particles in as-cast composite reduced from 25 and 30 μm to about 6 and 7 μm, respectively in 5-pass MDFed composites containing 4 and 8 wt. % Si. The mechanical properties results also showed work softening during the MDF where after two-pass MDF the hardness and tensile strength of the base sample reduced by 30 and 25%, while its elongation and toughness improved by 120 and 325%, respectively. In MDFed composites, the presence of SiP particles maintains the hardness and strength. According to the results, in the case of 2-pass MDFed composite containing 4 wt. % Si the hardness and tensile strength reduced by 18 and 2%, respectively, but the elongation and toughness increased by 25 and 175%, respectively.