On the effect of nanosized Al2O3 on the mechanical properties and microstructural evolution during friction stir extrusion of AA 6082 aluminum chips

Abstract

Friction stir extrusion (FSE), as a promising solid-state chip recycling technique, was employed to produce recycled wires from AA 6082 aluminum chips. Al₂O₃ reinforced and unreinforced wires with different tool rotations and vertical downforce were produced. The microstructure and texture evolution were studied using the electron backscattered diffraction (EBSD) technique. EBSD orientation maps showed that the microstructures developed a bimodal grain structure including fine recrystallized and non-recrystallized elongated grains. Grain orientation spread (GOS) EBSD maps demonstrated that the recrystallization was promoted in the presence of alumina second-phase nanoparticles. The resultant point-to-point and point-to-origin misorientation angle histograms indicated trivial misorientation differences proving the geometric dynamic recrystallization (GDRX) occurrence. The presence of loose high-angle grain boundaries (HAGBs) and accumulative misorientation angle inside the individual grains confirmed the continuous dynamic recrystallization (CDRX) occurrence. Moreover, grain boundary bulging was also visible through the microstructure, proving the activation of discontinuous dynamic recrystallization (DDRX). Texture analysis showed that simple a shear texture were introduced in the microstructure of the produced wires. The intensity of the obtained textures from the orientation distribution function (ODF) suggested that the application of the alumina particles improved the material flow during recycling. Micro-hardness measurements revealed that the addition of the alumina particles increased the hardness from 90 HV to 119 HV. Tensile testing showed a 20 % higher UTS for wires with alumina powders.