Recrystallization process of hot-extruded 6A02 aluminum alloy in solid and semi-solid temperature ranges

To provide the process parameters for preparing semi-solid billets, the impacts of heating temperature on recrystallization of a hot-extruded 6A02 aluminum alloy in solid and semi-solid temperature ranges were studied. The static recrystallization (SRX) even occurred at semi-solid temperature due to the low deformation ratio in the starting hot-extruded sample. Almost all elongated grains were transformed into equiaxed grains at immediate 630 °C. But not all grains with equiaxed shape were pure recrystallized grains, and small static recrystallized grain even emerged inside them. Bulk insoluble second particles including Fe, Mn, and Si were distributed at the grain boundaries. With the increasing of heating temperature, Vickers hardness increased firstly, then decreased and increased finally. And it was relevant with external force direction. According to the electron backscatter diffraction (EBSD) analysis, the fraction of the recrystallized, sub-structured and deformed grains changed little at 540 °C, but varied greatly at 600 °C and 630 °C. The contents of<111> and<100> fiber deformed textures as well as {100}<001> Cube texture showed analogical variation tendencies. The dislocation densities decreased roughly with temperature both from grain-based and kernel-based perspectives. Inhomogeneous deformation existed in an individual grain. Schmid factor had great relevance with external force direction and the gaps were narrowed by the equiaxed microstructure. In the isothermal deformation test, the liquid film was thickened and voids emerged in the shear-deformation region.