A comparative study of solid lubricant types on the microstructure and mechanical behaviour of AA7075-zirconium boride aerospace composites

Abstract

Aluminium alloy is the most favourable material for industrial usage because of outstanding low density, specific strength and resistance to oxidation. In this study, zirconium diboride (5 wt. % ZrB2) as hard ceramic particles and solid lubricants as hexagonal boron nitride (2.5 wt. % hBN) and tungsten disulfide (2.5 wt. % WS2) particles were used for fabrication of AA 7075 hybrid composite. The fabrication of hybrid composites is done through liquid metallurgy technique. The uniform distribution particles on matrix material were analysed through Optical Microscope (OM) and X-Ray Diffraction (XRD) was used to identify the phase of alloy and hybrid composite materials. The Micro Vickers hardness and tensile strength were used to evaluate the mechanical strength of alloy and composites. The microstructure of composites reveals fairly distributed ceramic and solid lubricant particles over the base matrix. The XRD peaks reveals presence of AA7075, ZrB2, hBN and WS2 with low intensity peaks. AA7075/ZrB2/WS2 composite shows an improved hardness and tensile strength as compared to AA7075/ZrB2/hBN composite. It was observed that the influence of WS2 on AA7075/ZrB2 composites have a higher bending strength than hBN composite and hBN particles offers easy grain movement during plastic deformation. Tensile fractured surfaces of alloy and hybrid composites were analysed through Scanning Electron Microscope (SEM). It reveals a ductile fracture in AA7075 alloy whereas ductile-brittle is observed in hybrid composites.