Effect of friction stir processing of in-situ A356/Al3Ni composites: microstructure refinement and wear behavior

This research investigated the impact of friction stir processing on grain refinement in the surface layer of composite materials. The in-situ composite was created by stir casting, incorporating 15% pure Ni into the Al matrix type A356. Microstructural analysis performed with optical microscopy and X-ray diffraction revealed the formation and dispersion of intermetallic phases such as AlNi, Al3Ni, and Al3Ni2, contributing to significant grain refinement. FSP further enhanced the micros structure by breaking and uniformly distributing small particles, including the primary Si phase and Al₃Ni, while refining α-Al dendrites. These microstructural changes resulted in improved mechanical properties, including a 13.81% increase in hardness for the A356/Al3Ni composite and a 14.47% increase for the base A356 alloy. Wear rate tests were conducted using a ball-on-disc apparatus under dry sliding conditions for both the base alloy A356 and the in-situ composite A356/Al3Ni, before and after FSP. Compared to the base alloy A356 and in situ composites before and after friction stir processing, the in-situ composite (A356/Al3Ni) after FSP exhibited a lower wear rate. However, during the wear test, the coefficient of friction decreased as the applied load increased for the base alloy A356 and the in-situ composite (A356/Al3Ni) following the friction stir process.