Vacuum-oxygen-low recycling process of aluminium composites manufactured from steel machining chips

Metal machining workshops generate a lot of metal chips, which pose both health and disposal challenges. Herein, for the first time, we demonstrate a novel process of reusing lathe-turning steel chips to manufacture high-compression strength Al alloy/steel composites. The process involves melting aluminium alloy onto the steel chips under vacuum and argon gas conditions. Clean and dried steel chips are packed inside a mould with a top layer of aluminium alloy pieces at three different quantity ratios of 80%Al/20% steel, 20%Al/80% steel and 50%Al/50% steel. The steel mould is then heated in a furnace at 650–700 °C until the aluminium metal melts. After a predetermined time of melting, argon gas is bubbled into the top layer (molten aluminium) of the mould while vacuum pumping is activated on the lower side of the mould (steel chips) for 5 min. The sample is allowed to cool within the mould. The composite containing 50%Al/50% steel has the highest mechanical properties with compression strength twice that of the other two samples. The microstructural observations revealed a good bonding between the steel chips and the Al alloy matrix. The study further presents the machinability of the samples, and it is seen that the composites behave like the aluminium matrix alloy during a turning operation and therefore do not require a special machining operation. It is shown that through this method, machining chips of steel can be recycled into high-compression strength metal–metal composites. These materials have the potential for high-compression strength applications such as machine supports and high-impact cushions.