Investigation of mechanical, tribological properties and microstructure of Al7075-Al2O3-graphene and Al7075-ZrO2-Graphene hybrid composites

In this study, the effect of alumina (Al2O3), zirconia (ZrO2), and graphene reinforcements on the microstructure, mechanical (density, porosity, hardness, compressive strength), and tribological properties (mass loss, wear rate, friction coefficient) of composites were investigated. Al7075-ZrO2, Al7075-ZrO2-Graphene, Al7075-Al2O3 and Al7075-Al2O3-Graphene composites were fabricated by powder metallurgy and induction heat treatment methods. Also, the effects of reinforcement ratio and heat treatment type (sintering, induction heat treatment) on the microstructure, mechanical and tribological properties of the composites were examined in detail. As a result of mechanical and tribological tests; the highest apparent density (2,72 g/cm3), hardness (157±4 HV), compressive strength (443±7 MPa), and the lowest wear rate (1,1x10-4 mm3/Nm) values of Al7075-ZrO2 composites were achieved in sintered and induction heat treated Al7075-6%ZrO2 composites. In Al7075-Al2O3 composites, the highest mechanical and tribological properties (apparent density, hardness, compressive strength, wear rate) were achieved in Al7075-12%Al2O3 (2,7 g/cm3, 170±2 HV, 471±6 MPa, 0,9x10-4 mm3/Nm) composites. Then, Al7075-ZrO2 and Al7075-Al2O3 hybrid composites were produced by reinforcing the structure with graphene while keeping the reinforcement ratios (6 and 12 wt%) constant, which gave the highest properties. Graphene-reinforced hybrid composites have the highest mechanical and tribological properties (apparent density, porosity, hardness, compressive strength, and wear rate) were achieved in sintered and induction heat-treated Al7075-6%ZrO2-0,1%Graphene (2,74 g/cm3, 6,7%, 169±2 HV, 478±4 MPa, 1x10-4 mm3/Nm) and Al7075-12%Al2O3-0.1%Graphene (2,72 g/cm3, 7,5%, 178±1 HV, 486±4 MPa, 0,7x10-4 mm3/Nm) composites. After the 0,1 wt% reinforcement ratio, graphene particles with nano-size show a tendency to agglomerate due to electrostatic attraction forces, and a decrease in material properties is observed. In addition, significant increases in the mechanical and tribological properties have been obtained with induction heat treatment after sintering and this process has proven effective. Keywords: Powder Metallurgy, Al7075, Alumina, Zirconia, Graphene