Mechanical properties improvement in chip extrusion with integrated equal channel angular pressing

The direct conversion of aluminum alloy machining chips into finished or semi-finished products by hot extrusion is a promising approach to improve the energy balance of aluminum recycling and to overcome the problem of material loss during remelting. The aluminum chips are compacted to chip-based billets and extruded at an elevated temperature to chip-based aluminum extrudates. However, the mechanical properties of chip-based aluminum extrudates produced with conventional extrusion dies are often inferior compared to those of extruded cast billets. Critical factors to achieve sound bonding of the chips and therefore favorable mechanical properties of the chip-based extrudates, are the shear, pressure and strain affecting the chips during the extrusion process. In this thesis, the process of hot extrusion with integrated equal channel angular pressing (iECAP) was adapted for the processing of aluminum alloy machining chips. This concept integrates the process principle of ECAP into a hot extrusion die, which results in additional shear, strain and pressure affecting the processed material. An iECAP die was fabricated for the processing of aluminum alloy machining chips and the amount of strain and pressure affecting the chips during hot extrusion was analyzed. The chip-bonding quality and the mechanical properties of chip-based extrudates fabricated with the iECAP die were investigated and compared to those of chip-based extrudates fabricated with state-of-the-art extrusion dies. The mechanical properties of extruded cast billets were used as a reference to investigate the performance of the chip-based extrudates. Furthermore, the effect of heat treatment on the mechanical properties of chip-based extrudates and the feasibility to produce chip-based finished parts by hot extrusion of aluminum chips with subsequent cold extrusion were investigated.