Effect of heat and plastic deformation on the texture of a friction stir processed 6061-T6 aluminum alloy: A neutron diffraction study

Time-of-flight neutron diffraction was used to investigate the texture changes in the friction-stir processed (FSP) 6061-T6 aluminum-alloy plates. Two different specimens were prepared with a purpose of separating the effects of frictional heating and severe plastic deformation on the changes of the preferred orientation in the as-received rolled plates: (Case 1) a plate processed with both stirring pin and tool shoulder, i.e., a regular friction-stir welding plate subjected to both plastic deformation and frictional heating, and (Case 2) a plate processed only with the tool shoulder, i.e., subjected mainly to the frictional heating. The comparison among the reduced intensities of the diffraction peaks, which is proportional to the number of unit cells that are preferentially oriented to fulfill Bragg's law, provides insights to the texture variations at various locations of the FSP plates. The results show that, in Case I, the number of the unit cells with the (200) plane normal parallel to the normal direction of the plate (i.e., reduced intensity in the through-thickness direction) were significantly decreased while the number of the unit cells with the (111) plane normal parallel to the normal direction of the plate increased near the weld center line. On the other hand, the Case 2 does not show changes in the reduced intensities. The current results clearly show that only the severe plastic deformation from the stirring pin affects the preferred orientation during the friction-stir processing, while heating alone from the tool shoulder has little effects.