A review on solid-state recycling of aluminum machining chips and their morphology effect on recycled part quality

The increasing demand for sustainable manufacturing has revived the interest in solid-state recycling (SSR) as a promising alternative method for aluminum waste. In this context, chips generated during machining processes constitute a substantial portion of aluminum waste, offering significant potential for recycling and mitigating waste. However, the machining chip morphology significantly impacts the properties of chip-based recycled parts. This review paper examines the current state-of-the-art solid-state recycling methods, focusing on hot forging, extrusion, equal channel angular pressing, friction stir extrusion and field-assisted sintering. It investigates the impact of aluminum chip morphology on the properties of the directly recycled material, emphasizing the chip machining consequence on the final quality of the product. Several studies reported that the strain and operating temperature are the most influential factors in SSR processes, followed by chip size with an average length of less than 4 mm. Yet, the heating time up to 3 h also had a major impact on chip weld strength. The findings highlighted the significance of aluminum chip morphology in improving the quality of recycled material. The properties of direct recycled samples primarily depend on chip weld strength and microstructure. Overall, this study presented a comprehensive overview of the current state of solid-state recycling and emphasized the significance of chip morphology in advancing the recycling process. Consequently, it equips researchers with a valuable resource for developing effective strategies for sustainable recycling of aluminum chips with high quality.