Reproduction of Ultra-Fine Grains in Equal Channel Angular Pressed Al Alloy 5083 by Friction Stir Process

摘要

Friction stir processing (FSP) was applied to Equal Channel Angular (ECA) pressed Al alloy 5083. The distributions of hardness and microstructure were examined in the FSPed material, and then an effect of FSP on the microstructure associated with hardness was discussed. ECA pressing gave fine dislocation cells with a high density of dislocations to Al alloy 5083, which resulted in a much higher hardness than the starting material. FSP produced ultra-fine recrystallized grains and subgrains in the stir zone and the thermo-mechanically affected zone (TMAZ), respectively. The recrystallized grain size in the stir zone decreased with decreasing rotation speed of the tool. The stir zone produced at the low rotation speed showed roughly the same hardness as the ECA-pressed material. The subgrains in the TMAZ reduced hardness value, but the hardness was higher than that of the starting material. The hardness increased with decreasing the grain size in the stir zone, which was expressed by the Hall-Petch relationship with a knick point. The slope change in the Hall-Petch relationship was due to distribution of fine particles. The two slopes were determined by the alternative of grain size or average distance between fine particles.