Review of solid state recycling of aluminum chips

In contrast with the conventional remelting recycling of aluminum and its alloy chips, the solid state recycling techniques, which can convert the chips directly into dense bulk materials, have attracted significant attention primarily because it possesses many advantages including lower energy consumption, lower metal loss as well as almost no emissions of harmful gases and solid wasters. In this keynote paper, with a view to the current researches of the solid state recycling techniques based on the severe plastic deformation (SPD) and powder metallurgy (P/M), the characteristics and applications of several typical methods, such as hot extrusion, equal channel angular pressing (ECAP), cyclic extrusion compression (CEC), friction stir extrusion (FSE), high pressure torsion (HPT), screw extrusion and spark plasma sintering (SPS), are introduced. A growing number of researches and literatures suggest that the mechanical properties of solid state recycled specimens are primarily dependent on the chip bonding quality and microstructure of the corresponding bulk materials. Then, the mechanism analysis of consolidation of chips is carried out, and three relevant theoretical modes, characterizing the bonding quality, are also mentioned. Moreover, the factors influencing the density and microstructure of chip consolidated product are discussed comprehensively. Eventually, recommendations in the improvement of solid state recycling techniques and the future prospects are put forward.