Insights into the microstructure evolution and micromechanical properties of friction stir consolidated AA6082 aluminum chips

Friction stir consolidation (FSC) is a relatively new solid-state recycling process developed to obtain small billets from metal chips in a unique working step. One of the main unresolved issues in solid-state recycling processes (e.g., Friction Stir Extrusion, Continuous Friction Extrusion, etc.) is the understanding of the effects of the oxide layers initially present on the chips on the final recycled products. In this paper, FSC was conducted on AA 6082 aluminum chips with different rotational speeds of 1000, 1500, 2000, and 2500 rpm. Microstructural evolution was examined using scanning electron microscopy (SEM) integrated with electron backscattered diffraction (EBSD). Backscattered electron (BSE) images showed that fine equiaxed grain structures were developed through the microstructure of the processed samples. Intermetallic compounds were broken down by the stirring action of the rotating tool, leading to the formation of micro- and nano-sized second-phase particles. The presence of loose high-angle grain boundaries connected to low-angle grain boundaries confirmed the occurrence of continuous dynamic recrystallization (CDRX). Texture analysis revealed the development of simple shear texture components of face-centered cubic (FCC) structured materials with the Oblique Cube component. Hardness measurements revealed that the hardness of the microstructure increased with a greater proportion of low-angle grain boundaries (LAGBs) and higher texture intensity.