Wear performance of nano-Al2O3 particles and CNTs reinforced magnesium matrix composites by friction stir processing

To improve the wear resistance of magnesium alloys, nano-alumina (n-Al2O3) particles and carbon nano-tubes (CNTs) reinforced AZ31 magnesium alloy matrix composites and hybrid composites were fabricated by friction stir processing (FSP), and the friction and wear performance was investigated. The composites contain reinforcement of 0.3%CNTs, 0.1%A12O3+0.2%CNTs, 0.15%A12O3+0.15%CNTs, 0.2%A12O3+0.1%CNTs and 0.3% A12O3. The dry wear tests were carried out at room temperature, with the normal load of 0.65 Mpa, 1.30 MPa, 1.95 MPa, 2.60 MPa and 3.25 MPa, correspondingly. The counterface material was 5140 alloy steel. The microstructure of the fabricated composites was void of obvious defect, with the reinforcements evenly distributed in the matrix. All the composites were more resistant in wear than FSP AZ31 alloy. The wear of the n-Al2O3 independently reinforced composite is lower than that of the CNTs independently reinforced composite; however, its friction coefficient is higher. Certain combination of n-A12O3 and CNTs possessed hybrid effect on the wear performance of the hybrid composites, because they had hybrid effect on the hardness and friction coefficient of the composites. When the load was higher than 1.95 MPa, the wear of (0.1%A12O3+0.2%CNTs)/AZ31 hybrid composite was considerably lower than those of other composites and its friction coefficient was obviously lower than those of other composites. The wear mechanism of the composites was abrasive wear when the normal load was lower than 1.30 MPa; otherwise it was delamination wear of the mechanically mixed layer.