Synthesis and characterization of graphene nanoplatelets reinforced AA7068 matrix nanocomposites produced by liquid metallurgy route

In this paper, we report the synthesis of graphene nanoplatelets (GNPs) reinforced AA7068 metal matrix nanocomposites by a combination of ultrasonication, powder and liquid metallurgy techniques. The effect of GNPs with a varying weight fraction (0.1, 0.3, 0.5, 0.7 and 1 wt%) on microstructure, mechanical and tribological properties of AA7068 metal matrix is studied. In addition to this the developed nanocomposites were subjected to the standard T6 heat treatment conditions and its effect on aforementioned properties was also studied. Mechanical properties of as cast and T6 heat treated nanocomposites showed increase in tensile strength and elongation values up to 0.5 wt% GNPs reinforced AA7068 nanocomposites, thereafter drop in these properties was observed. A similar behavior was observed in case of grain size, where grain refinement of AA7068 matrix by GNPs reached saturation point for 0.5 wt%. The average ultimate tensile strength (UTS) of the specimens before and after extrusion processes and T6 heat treatment increases from 263 MPa to 372 MPa and 495-615 MPa after adding 0.5 wt% GNPs, respectively. Finally, the wear resistance of the AA7068 alloy and its nanocomposite with 0.5 wt% GNPs in T6 conditions was significantly higher than that of as cast conditions. The obtained results indicate that GNPs (up to 0.5 wt%) are effective in improving the mechanical properties and wear resistance of AA7068 metal matrix in both as cast and T6 conditions.