Microstructure and Tensile Behavior of Al7075/Al Composites Consolidated from Machining Chips Using HPT: A Way of Solid-State Recycling

In this study the feasibility of using high-pressure torsion (HPT) process as a suitable technique for solid-state recycling of Al alloy machining chips has been evaluated. One and four turns of HPT were used for consolidation of 7075 Al alloy chips/commercially pure Al powder mixtures at room temperature. The prepared mixtures included different weight fraction of chips in the range from 20 to 100%. The samples were fabricated from either annealed or non-annealed chips. Additionally, the effect of the fraction of 7075 Al chips on the density, microstructure and tensile behavior of the consolidated samples was investigated. It was found that the addition of pure aluminum powder played an important role as a binder in the consolidation process and yielded improved mechanical properties due to creating lower porosity and better bonding between the chips. Tensile tests revealed that the highest ultimate tensile strength and fracture strain were obtained for the composite containing near 50 wt% annealed 7075 Al chips, and fabricated through 4 turns of HPT. Optical microscopy investigations demonstrated that these conditions resulted in a fine microstructure with uniform distribution of chips. Graphic