Investigation of strength and microstructural evaluation of friction stir processed AA6061 alloy surface composite reinforced with tungsten carbide and nitinol particles

The widespread use of AA6061 alloy as a demanding tribological part in aeronautics and automobiles is greatly limited by its low wear resistance and low surface hardness. This research work was carried out to manufacture AA6061 surface composites using the Friction Stir Processing (FSP). A dual-reinforcement approach of ultra-hard Tungsten Carbide (WC) and pseudoelastic Nitinol (NiTi) nanoscale powders was used. Reinforcement weight fractions of 0, 1, and 3 wt-% and traverse speeds of 15, 20, and 25 mm min–1 were investigated. Microstructural evaluation showed significant grain refinement from dynamic recrystallisation and Zener pinning. Although the peak microhardness of the 3 wt-% hybrid composite was as high as 158.4 HV0.1, it exhibited pronounced agglomeration and embrittlement. On the contrary, 1 wt-% composite produced at a processing rate of 20 mm min–1 showed the best mechanical performance, with a yield strength of 175 MPa and an ultimate tensile strength of 230 MPa, an increase of 25%. Moreover, the specific wear rate changed to 9.69 × 10−6 mm3 Nm–1 and corresponded to a switch of the wear mechanism from adhesive smearing to abrasion; the tribolayer was stabilised using the hybrid reinforcement, resulting in a decrease of the coefficient of friction to 0.22.