Enhancement strength of AZ91 magnesium alloy composites reinforced with graphene by T6 heat treatment and equal channel angular pressing

In this study, we investigated the use of graphene as a reinforcement material in magnesium alloy (AZ91) composites. The composites were prepared through stir-casting followed by a novel strength improvement process using T6 heat treatment and equal channel angular pressing (ECAP). Microstructural analysis through X-ray diffraction and scanning electron microscopy combined with energy-dispersive X-ray spectroscopy substantiates new phases, including magnesium carbide (MgC₂), which produce enhanced mechanical properties along with grain refinement after T6 heat treatment and ECAP. The addition of graphene increased the mechanical properties of the samples to 0.1 wt% graphene in the as-cast sample. However, the hardness and strength of 0.2 wt% graphene decreased because of agglomeration under the as-cast condition. Following two passes of ECAP, a 49.22% increase in hardness was observed in the composite, whereas the yield and ultimate tensile strength increased by 64.38% and 80.42%, respectively. The load transfer mechanism contributed to the strengthening of the AZ91/graphene composites and exhibited satisfactory interfacial bonding between the matrix and reinforcement. Ductile fractures were predominantly observed in T6- and ECAP-treated samples.