Producing a novel alumina reinforced aluminium matrix composite from aluminium machining waste

Abstract

This study explores an innovative approach to producing alumina-reinforced aluminium matrix composites (AMCs) directly utilising aluminium alloy machining waste as the primary raw material. By leveraging the machining waste, this research addresses material sustainability and aligns with circular economy principles, minimising resource wastage and promoting environmental sustainability. The focus is on enhancing the naturally occurring alumina on the swarf surface through specific treatments to improve the composite's overall properties. The research methodology employs a multi-technique analysis to monitor and adjust the processing conditions, ensuring optimal material characteristics. Initially, the aluminium swarf is subjected to high-temperature treatment, followed by Equal Channel Angular Pressing (ECAP) to consolidate the material into a dense, uniform composite. X-ray diffraction (XRD) analysis identifies the phase composition, revealing the transformation of alumina polymorphs under different thermal conditions. Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM-EDS) maps the elemental and phase distribution, assessing the interaction between alumina reinforcement and the aluminium matrix. Polarised light observation and Electron Backscatter Diffraction (EBSD) are utilised to evaluate grain refinement, microstructure, and texture, providing insights into the composite's mechanical behaviour. Key findings indicate that heat treating the aluminium swarf at 650 °C for 2 hours results in the formation of gamma alumina only on the surface. Increasing the temperature to 850 °C transitions the alumina to the alpha phase, known for its superior mechanical properties. Four passes of ECAP using route C effectively consolidate the treated swarf into a composite with no visible macro-porosity, although microporosity around the alumina particulates is still observed. This suggests that while 4 passes, ECAP successfully breaks alumina films and welds adjacent swarfs, this number of passes fails to remove microporosity that could influence the composite's mechanical properties. The composite's performance is further evaluated through tensile and hardness tests, confirming the significant impact of processing conditions on the material's mechanical behaviour. The presence of alpha alumina, achieved through precise heat treatment and the composite's consolidation via ECAP, contributes to enhanced tensile strength and hardness compared to composites with gamma alumina or those processed under less rigorous conditions. This research contributes to the field of materials science by providing a novel method for repurposing aluminium machining waste into high-value composite materials. By optimising the processing conditions, particularly the heat treatment temperature and the application of ECAP, it is possible to produce AMCs with improved mechanical properties suitable for various high-performance applications. Moreover, this study highlights the potential of using advanced material characterisation techniques to understand the microstructural evolution of composites, guiding the development of more sustainable and efficient manufacturing processes. In conclusion, this study presents a sustainable approach to manufacturing alumina-reinforced AMCs using aluminium machining waste enhanced by high-temperature treatment and ECAP. The findings underscore the importance of processing conditions in determining the composite's microstructure and mechanical properties, offering insights into developing new materials contributing to the circular economy. Future research could explore the long-term performance of these composites in real-world applications and further refine processing techniques to minimise microporosity and enhance material properties.