Effect of Heat Treatment on Microstructure and Hardness of Graphene Nanoplatelets Reinforced Al-Zn-Mg-Cu Alloy Composite

Abstract

Excellent mechanical, electrical, and thermal properties of the sp2 hybridized carbon allotrope derivative of graphene nanoplatelets (GNP) make it a suitable reinforcement candidate for the metal matrix composite. Due to the superior properties of Al – Zn – Mg – Cu alloy, it is used as an armor material for decades in defense industries. In this study, Al – Zn – Mg – Cu alloy/GNP reinforced composite with varying weight fraction of 0, 0.5% & 1% GNP was fabricated via hot-pressing sintering. Initial investigation shows that the composites were densified, and the relative density was 99.64% after the fabrication process. Two-stage heat treatment was performed on the Al alloy, forming a stable η (MgZn2) phase. The DSC plots show the dissolution of the unstable η´ (Mg4Zn7) phase into the stable η (MgZn2) phase in between 450 °C – 480 °C and homogenized due to artificial aging process with the α-Al phase. Investigation showed an increment in the hardness of the heat-treated 0.5% GNP reinforced composite by 15.44%, and 8.92% in the heat-treated 1% GNP reinforced composite compared to their non-heat treated composites. The Field Emission Scanning Electron Microscopic images of samples before heat treatment show agglomeration of GNP and heterogeneous nucleation, and images after heat treatment show that GNP has been dispersed into the grains and grain boundaries alongside the eutectic phases, which restrict the dislocation motion and strengthen the matrix by grain boundary strengthening.