The effect of microstructure and texture evolution on the hardness properties of the cold rolled AA7075-T6 aluminum alloy during the friction stir processing

In this study, microstructure and micro/macro texture evolution in an AA7075 aluminum alloy during FSP were investigated. Also, the effect of tool traverse speed on the texture and its dependent mechanical properties of this alloy, especially on the friction stir zone (SZ), were experimentally determined. For this purpose, the FSP was done at three tool traverse speeds (12.5, 50, and 100 mm min(-1)) in a single pass and under a constant tool rotation speed (500 rpm). Hardness in the SZ (similar to 105 HV) was measured higher than the base metal (similar to 85 HV). Microstructural observations revealed that fine grains were formed due to the growth inhibition during the dynamic recrystallization because of the high cooling rate in the SZ. It was also found that the SZ had the fine equiaxed grains which their size decreased with an increase in the tool traverse speed. On the other hand, it is shown that the hardness evolution during the FSP in heat treatable Al-alloys greatly depends on the precipitates distribution and only slightly on the grains and dislocations structure. Therefore, a change in the density of grain boundaries and the precipitates distribution can be affected on the hardness due to the dislocations interacting with the grain boundaries. In addition, texture evolution in the samples was investigated by pole figures. These results showed that the cold rolled base metal (BM) with the two components of {211} < 111 > and {123} < 634 > changed to typical {100} < 001 > and {001 } < 110 > recrystallized textures during the FSP.