Characterization of marble waste and graphene oxide reinforced LM6 aluminum composites fabricated by stir squeeze casting process

Abstract

Applications of aluminum matrix composites (AMC) in automobile and aerospace industries have been increasing due to their attractive properties such as lightweight, high specific modulus, stiffness and good corrosion resistance. However, the cost is the key factor in making composite materials due to the higher cost of reinforcement materials. The reuse of industrial waste, which is otherwise dumped as landfills, can reduce the composite production costs and the pollution levels posed by landfills. Therefore, this research aims to use industrial waste and graphene oxide as reinforcement phase materials to develop new and cost-effective AMC materials. In this study, LM6 aluminum alloy was used as a matrix phase, and industrial waste material of marble waste (MW) and a distinct novel material of graphene oxide (GO) with 5 wt % of each reinforcement were used for composite development. The hybrid stir and squeeze casting method was used to develop the new composites with the use of optimum casting process parameters derived from the DoE (Taguchi coupled with ANOVA) technique, integrated with Statistical Process Control (SPC) Excel software. Mechanical testing of developed AMC such as tensile, impact and hardness were performed according to ASTM- E8/EM8-13, ASTM- E23-16b and ASTM-E18 standards, respectively. The microstructural and morphological analysis were done using optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) techniques. Further, fractography analysis was performed on the tensile fractured surface of both composite materials using SEM equipped with JED-2300 Analysis Station Plus. Finally, a cost model for the composite fabrication process was developed and compared with fly ash and SiC-reinforced composite materials in order to draw valuable insights on the production cost of the new composites. From the evaluation of the DoE-ANOVA results, it was confirmed that stirring speed of 600 rpm, stirring time of 10 min, and melting temperature of 740 oC have had a significant influence on the response variables of LM6 composites. Mechanical test results showed that there was an increase of 16% in UTS for LM6+5%MW and 41.8% for LM6+5%GO as compared to LM6 aluminum alloy. For hardness property values, around 25.34% increase was witnessed in both composites equally compared to LM6 with the hardness value of 75.52, 94.66 and 94.68 (HRF) for LM6, LM6+5%MW and LM6+5%GO respectively. The enhanced mechanical properties were duly supported by the microstructures of both composites captured using OM, SEM, EDS and XRD. The degree of strengthening of LM6 aluminum alloy was determined by micrographs, chemical composition, particle size, and concentration of reinforcing phase materials. Subsequently, fractography analysis on tensile fractured composite samples showed no or minor cracks, thus observed that fracture was caused by matrix cracking, matrix cavitation, interface separation and rupture. The cost analysis demonstrated that the total reinforcement cost decreased by 44% due to the use of natural and industrial waste materials compared to fly ash and SiC reinforced composite materials. The current research reflected the concept of circular economy as applicable to the LM6 composites to maximize the usefulness of the waste materials. Therefore, the research concluded that MW and GO are prospective alternate candidates as reinforcements in the LM6 matrix phase to develop composites with enhanced mechanical properties suitable for automobile, aerospace and maritime industries.