Effect of precipitation hardening on wear behavior of premix Al7075 hybrid matrix composites

Abstract

Al 7075 alloy is high strength alloy with excellent physical and mechanical properties. Though the alloy has capacity to work as structural material, many a times poor tribological properties limit its applications. Tribological properties can be improved by addition of hard ceramic reinforcement or by adding soft solid lubricants. But this solitary addition shows improvement at the cost of certain mechanical properties.In this study, premix alloy of Al 7075 was fabricated by blending elemental powders followed by Hot Press Sintering (HPS). The optimum operating window for HPS at 550 °C, 40 MPa for 6 min was used to obtain maximum densification. Al 7075–10 wt% B4C (ABC 10) was used as starting material for development of Hybrid Matrix Composites namely (HMC-G) and HMC-M containing solid lubricants viz. Graphite and MoS2 (1 to 5 % by wt.) respectively. Post sintering heat treatment consisting of solutionising at 480 °C followed by artificially ageing at 120 °C for 24 h was employed. The wear tests were carried out in Pin on Disc (POD) machine at various combination of sliding speeds (1, 1.5, 2, 2.5 m/s) and applied loads (10, 20, 30, 40 N) with constant sliding distance of 3000 m. These composites were then characterized for hardness and density measurement, microstructures, SEM-EDS and worn-out feature analysis. Surface response analysis was done to locate mild wear and severe regimes. Hybrid matrix composites containing 3 % wt. of MoS2/Graphite in ABC 10 shows improved wear resistance due to synergistic effect of dispersion and precipitation strengthening.