A Study on the Effect of Ageing Heat Treatment on Hardness, Tensile and Corrosion Behaviour of Stir-Cast AZ91D–5SiC–1Gr Hybrid Magnesium Composite

In this present study AZ91D magnesium alloy and AZ91D–5SiC–1Gr (wt%) hybrid metal matrix composite were produced through the stir casting process. Microstructural studies were carried out through X-ray diffraction (XRD), scanning electron microscope (SEM) and SEM with energy-dispersive X-ray analysis (EDAX). XRD study indicated the spinel crystal structure with double substitution of cubic and hexagonal closed pack materials. Ageing heat treatment comprising natural ageing (T4) and artificial ageing (T6) for 24 h was carried out on the materials. Both T4 and T6 heat-treated samples exhibited higher hardness than as-cast samples. Maximum hardness 88.8 ± 2.3 BHN and 129.9 ± 3.27 BHN were obtained for T6 heat-treated alloy and hybrid composite, respectively. Tensile properties of samples were evaluated by their stress–strain curves. Maximum values of ultimate tensile strength, yield strength (0.2%) and ductility obtained for T6 heat-treated hybrid composite were 193 MPa, 87.1 MPa and 11%, respectively. Corrosion behaviour of the samples was evaluated by the electrochemical polarization curves obtained through Tafel extrapolation method. Both the alloy and hybrid composite exhibited improved corrosion resistance as a result of natural ageing (T4) and artificial ageing (T6) heat treatment processes. Lowest corrosion rates 0.071 mm/year and 0.074 mm/year were obtained for AZ91D alloy and AZ91D–5SiC–1Gr (wt%) hybrid composite, respectively.