Cold extrusion of hot extruded aluminum chips

Abstract

The direct conversion of aluminum alloy machining chips into finished parts by hot extrusion with subsequent cold extrusion was investigated. While the process of hot extrusion was utilized to break the oxides covering the individual chips and to lead to bonding of the pure metal, the processes of cold forward rod extrusion as well as cold backward can extrusion were used for the production of chip-based finished parts. For the hot extrusion process, a flat face die and a die with integrated equal channel angular pressing (iECAP die) were used in order to investigate the influence of the deformation route on the quality of the chip-based finished parts. The flat-face die is a conventional tool for the fabrication of solid sections, while the iECAP die is an experimental tool that integrates the severe plastic deformation process of equal channel angular pressing into a conventional hot extrusion die. Tensile tests revealed superior mechanical properties of chips extruded through the iECAP die compared to those of chips extruded through the flat-face die. The hot extruded chips were further processed at room temperature by either backward can extrusion to cans with different wall thicknesses or by forward rod extrusion to shafts with different values of extrusion ratio and cone angle. For all fabricated chip-based finished parts, the mechanical properties and the microstructure were analyzed. Backward can extrusion of chip-based extrudates fabricated with the iECAP die resulted in defect-free cans for all investigated wall thicknesses, while the cans obtained from flat-face die processed chips showed cracks within the walls. Shafts without visible internal defects could be produced by forward rod extrusion of previously hot extruded chips, independent of the hot extrusion die design. However, subsequent compression tests revealed a dependency of the mechanical properties of chip-based shafts on the hot extrusion die design.