Mechanical Behaviour and Morphology of Thixoformed Aluminium Alloy Reinforced by Graphene

Abstract

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.

Influence of Graphene on the Microstructure and Mechanical Properties of Aluminium Matrix Composite

“…The microstructure becomes closely packed, there are fewer gaps between boundaries, and the presence of porosity will be reduced [16]. The grain refinement will enhance the strength and plasticity of Al alloy [17]. When the aluminium atoms organize into a crystalline structure during the alloy's solidification, the α -Al phase is created.…”

Effect of Short Heat Treatments on the Microstructural Evolution and Hardness of Thixoformed Graphene Reinforced Aluminium Composites

“…The billet of semi-solid material with thixotropic properties experiences the shear force and produces the thixoformed billet with the detachment of dendritic arms with a multiplied grain (Arif et al 2020;Putra, Manaf & Prajitno 2022;Samat et al 2021). Md Ali et al (2022) employed the thixoforming process to fabricate a GNPreinforced A356 matrix composite. Their results indicate that applying the thixoforming process increased the relative density of the composite and significantly enhanced its mechanical properties.…”

Effect of Magnesium Addition by Thixoforming Process on Wear Properties of A319 Alloy

“…On the other hand, modi cation of chemical composition based on commercial alloy (e.g. A356 and A319) in aluminium alloy affects the rheological behaviour and the microstructure changes during the thixoforming process [23,24]. In this process, the size and morphology of α-Al are re ned, the distribution is uniform, and needle-like Si particles are transformed into more regular morphologies due to the lower processing temperature used than conventional casting [25].…”