Considerable attention has been given to graphene as a reinforcement material for metal matrix composite (MMC) because of its great potential for use in the automotive and aerospace industry. In general, the difficulty in achieving optimally improved properties can be attributed to poor wettability, agglomerations, and non-uniform distribution of reinforcement in the MMCs. Therefore, in terms of structural integrity, interfacial bonding, and its strengthening mechanism are important to achieve a high performance composite, which makes it imperative to discuss the integration of graphene into the alloy. The reinforcement mechanism of graphene-reinforced aluminium alloy has been evaluated in a limited number of studies, and this article examines current publications in this area. This article outlines three key topics related to the key challenges of graphene as a reinforcement material, the strengthening mechanism of graphene in a metal matrix, and the factors limiting the properties enhancement. Lastly, future works and recommendations addressed are summarized. The review presented aims to benefit to a wide range of industries and researchers and serve as a resource for future scholars.

Hemp hurd, also commonly referred to as hemp shives, is a low cost byproduct from the decortication process of hemp, retailing for less than 0.2 $/kg. In the context of establishing a hemp agri-fibre operation, value adding to this underutilized waste stream is crucial to improve the overall economics of the operation. In this research the use of hemp hurd as an alternative to wood flour for the production of wood plastic composites is investigated. Hemp hurd filled Polypropylene composites were produced via compounding in a co-rotating twin screw extruder. Taguchi design of experiment methodology in combination with Analysis of Means (ANOM) was used to gain an understanding of the influence of the different processing parameters. Parameters investigated were screw-configuration, temperature profile and fibre loading. Best results were obtained with a relatively gentle mixing zone at a temperature of 200 ⁰C and 40%wt. and 20%wt. of fibre loading for highest stiffness and highest strength respectively.

Thixoforming is a promising method that offers several advantages over both liquid and solid processing. This process utilizes semi-solid behaviour and reduces macrosegregation, porosity and forming forces during the shaping process. Microstructural and mechanical characterization of 0.3, 0.5 and 1.0 wt% graphene nanoplatelet (GNP) reinforced A356 aluminium alloy composite fabricated by thixoforming was investigated. Stir casting was employed to fabricate feedstocks before they were thixoformed at 50% liquid. The microstructure was characterized and evaluated by field emission scanning electron microscopy with an energy dispersive X-ray detector and X-ray diffraction. Mechanical testing, such as microhardness and tensile testing, was also performed to estimate the mechanical properties of the composites. The incorporation of 0.3 wt.% GNPs in Al alloy increased by about 27% in ultimate tensile strength and 29% in hardness. The enhancement in tensile strength is primarily attributed to load transfer strengthening due to the uniform dispersion of these GNPs within the Al matrix, which promotes effective load transfer during tensile deformation, and GNPs’ wrinkled surface structure. Simultaneously, the addition of GNPs enhances the grain refinement effect of the Al alloy matrix, resulting in a grain size strengthening mechanism of the GNPs/Al composites. The results reveal that thixoformed composite microstructure consists of uniformly distributed GNPs, α-Al globules and fine fibrous Si particles. The composites’ grains were refined and equiaxed, and the mechanical properties were improved significantly. This study creates a new method for incorporating GNPs into Al alloy for high-performance composites.

The recent advancement in graphene-reinforced aluminium matrix composites improves wear behaviour in the production of lightweight and high-performance nanocomposites. Considerable works have been devoted to using graphene nanoparticles as solid self-lubricants to increase wear resistance, minimise friction coefficients, improve service efficiency, and extend the lifespan of related sliding components. In general, wear behaviour often depends on the homogeneous distribution of graphene in the aluminium matrix. The non-uniform distribution of reinforcement due to the tendency of graphene to agglomerate in aluminium matrix and its poor wettability becomes a challenge in developing optimum functional of composites. The wettability of graphene can be enhanced by proper processing methods and sufficient addition of magnesium that can improve the wear and frictional properties of the produced composites. Hence, this review article provides recent findings and the influence of graphene as reinforcement materials in composites, including the effects on wear behaviour and friction properties. This article also discusses new advancements in the effect of graphene in self-lubricating aluminium matrix composites and the impact of reinforcement on the wear mechanisms of the composites. The future direction of the wear properties of MMCs is also covered at the end of the review.