Dynamic restoration and microstructural evolution during hot deformation of a P/M Al6063 alloy

Hot deformation behavior of Al6063 alloy produced by direct powder extrusion was studied by means of uniaxial compression test in the temperature range between 300 and 450 °C and strain rate range between 0.01 and 1 s−1. Electron backscatter diffraction (EBSD) technique and transmission electron microscopy (TEM) were utilized to study the microstructure of the material before and after the hot deformation. The microstructure of the extruded alloy consisted of elongated grains within a subgrain structure and small grains free of low angle grain boundaries (LAGBs). An equiaxed duplex microstructure consisting of large substructured grains and fine grains separated by high angle grain boundaries (HAGBs) were observed after hot deformation. Evaluation of the hot-deformation activation energy using a hyperbolic sine law yielded a value of 198 kJ mol−1. The kinetic analysis and microstructural changes suggest that dynamic restoration mechanisms, i.e., dynamic recovery (DRV) and dynamic recrystallization (DRX), are operative to cause flow softening during hot compression. Correlations between Zener–Hollomon parameters and the size of subgrains and recrystallized grains were established. It was found that DRV prevailingly occurred at high Z values (Z > 1.12 × 1016) while DRX was the dominant mechanism at the low Z values.