In the present study, nickel (Ni) and graphene nanoplatelets (GNPs) are considered as ideal reinforcements for Mg-9Al-1Zn (AZ91D) magnesium alloy to form metal matrix composites (MMCs) because of their excellent mechanical properties. It is essential to utilize effective manufacturing techniques to develop AZ91D magnesium (Mg) alloy-nickel-graphene nanoplatelets (AZ91Z-Ni-GNPs) MMCs. Hence, the spark plasma sintering method is used to fabricate AZ91D-Ni-GNPs composites. HRTEM, OM, SEM, EDS, XRD, and Raman spectroscopy were used to investigate the microstructure, crystallinity, and elemental composition of both the blended powder and the sintered composites. GNPs and Ni were well-dispersed in the AZ91D Mg matrix, and effective interfacial bonding is formed between GNPs, Ni, and Mg alloy matrix powder before sintering. A Response Surface Methodology (RSM) with a central composite design was used to design the experiments by considering two variables, i.e., sintering temperature and pressure. The method was adopted to eliminate the trial-by-error approach. Using the data generated, quadratic regression models were developed for the relative density (g/cm3), and Vickers hardness (HV) of the MMCs, and the parametric effects were explained via RSM. The process parameters were optimized, and the effective interaction between two descriptive variables (process parameters) on the relative density, hardness, and microstructural properties of Mg-based composites was investigated. Validation of the experimental run was performed using optimal process parameters acquired from the analyses to demonstrate the enhancement in the properties of the sintered composites. It was observed that the sintering temperature had a major influence on the relative density and hardness properties (responses). The optimal relative density and hardness obtained for AZ91D-Ni-GNPs composites were 1.723 g/cm3 and 93.21 HV, respectively. The addition of GNPs to AZ91D-Ni produced material with improved properties.
The Department of Chemical Engineering of the University of Pretoria and Faculty of Engineering, the Built Environment and Information Technology, Pretoria, South Africa.
