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.
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.
This study focuses on the analysis of fill time by optimizing the injection molding parameters to reduce the defects that are always found on the plastics part such as poor weld line and part not completely filling which can contribute to mechanical properties of the plastic part. The parameters selected for this study are melting temperature, mold temperature, injection time, and the number of gate positions. Response Surface Method (RSM) was used to determine the most significant and optimum parameters on the fill time. From the result analysis, it is found that the injection time is the most significant parameter that affected the fill time with a 99% contribution. The result shows that there is no interaction between process parameters toward fill time which the injection time is the only major factor that affects the fill time. The improvement increases by 0.07% after the optimization process from 4.278s to 4.281s. The most optimum parameters to longer the injection time are mold temperature at 60°C, injection time at 4s, and the number of the gate with two gates position. Thus, the longer the injection time, it can reduce the defect of molded part in the injection molding process.
The potential of binary Mg-Ca alloy as biodegradable material is considerable interest in implant application among researchers. This research was conducted to investigate the effect of different forging temperature and forging speed on the hardness, microstructure and corrosion rate of Mg-0.7%Ca. The experiment was established by preparing the alloy sample with 0.7%wt calcium content. The forging process was carried out under four different temperature variations of 140°C, 180°C, 220°C, and 260°C (±10°C) with two different speed;25 and 45 strokes per minute (spm). The samples microstructure was examined by optical microscope and scanning electron microscope (SEM) equipped with energy dispersive X-ray (EDX). The mechanical properties of the forged samples were measured in its hardness and plastic deformation ability along with samples cold-working percentage. The corrosion rate was determined by performing the electrochemical test in simulated body fluid. This research found that increases of forging temperature and forging speed provide a higher rate of recrystallization and Mg2Ca compound precipitation results in greater hardness, increase deformation and reduce the cold-working percentage. However, the investigated factors still led to a high corrosion rate compared to a previous study and consequently, reduce the feasibility of the alloy in implant application for biodegradable material.
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