The influence of deformation-dependent prior chip boundary on microstructure and tensile properties in a solid-state recycled AA6063 aluminum alloy

Abstract

Solid-state recycling that is devoid of metal melting process represents an energy-effective, environment-friendly and materials-saving way in producing sustainable aluminum (Al) materials from its scraps, and thereby is a promising solution in recycling of Al-based chips. On the recycling of Al-based chips by solid-state route, however, one major concern comes from the presence of prior chip boundaries which are expected to negatively influence the mechanical properties of recycled materials. In the current study, we examined prior chip boundaries in a solid-state recycled AA6063 Al alloy fabricated by extrusion of its machining chips, and found that samples taken from the edge and central regions of the extruded, artificially-aged rod exhibit drastically different oxide-decorated prior chip boundaries. The observed variations in oxide-decorated prior chip boundaries between the two locations are intimately linked to the shear strain encountered during the extrusion process. Adjacent to the edge region, a higher shear strain facilitates the fine dispersion of smaller oxides along the prior chip boundaries that are aligned with the extrusion direction. Conversely, in the central region, a reduced shear strain results in the coarse distribution of larger oxides fragments within the prior chip boundaries. As a result, the samples derived from the edge and central regions display essentially different grain structures, strain hardening effects, and fracture behaviors. Our results demonstrate deformation-controlled oxide-decorated prior chip boundaries in chip-based Al alloys, and their principal influence on recycled materials’ microstructures and tensile properties.