Microstructure and mechanical properties of multi-pass friction stir processed aluminum alloy 6063

Abstract

The effect of overlapping between consecutive passes of Friction Stir Processing (FSP) was examined on the microstructure, microtexture, and mechanical properties of Al 6063. FSP was carried out at three overlapping (OL) percentages, i.e. 25, 50, and 75, and at constant rotational and traverse speeds of the FSP tool. Microstructural analysis based on grain boundary misorientation distribution, grain size and microtexture were made by Electron Back Scattered Diffraction (EBSD), while mechanical properties were evaluated by microhardness and tensile tests. For the three OL percentages, similar grain refinement (in the range of 3–6μm) occurred in the processed zone. The microtexture measurements in the OL area show the formation of shear texture, having a stronger intensity of B/B¯ component by increasing the OL percentage. On the other hand, the tensile and microhardness tests indicate a reduction in the strength and microhardness of FSP samples with increasing the OL percentage due to the dissolution of the hardening precipitates. The overlapping effect was further evaluated on the thermal stability of microstructure, microtexture, and mechanical properties of FSP samples by applying solution heat-treatment and aging (SHTA). The results show that SHTA led to grain growth with an average grain size of 35μm. However, it caused limited weakening of the shear texture in the OL area with no sign of recrystallization. In addition, SHTA led to precipitate formation and thus restoring the strength and microhardness to the levels of the base metal.