The dislocation density and sub-grain size were determined in the base material and friction-stir welds of 6061-T6 aluminum alloy. High-resolution X-ray diffraction measurement was performed in the base material. The result of the line profile analysis of the X-ray diffraction peak shows that the dislocation density was about 4.5 x 1014 m−2 and the sub-grain size was about 200 nm. Meanwhile, neutron diffraction measurements were performed to observe the diffraction peaks during friction-stir welding (FSW). The deep penetration capability of the neutron permitted measurement of the peaks from the mid-plane of the Al plate underneath the tool shoulder of the friction-stir welds. The peak broadening analysis result using the Williamson–Hall method shows the dislocation density of about 3.2 x 1015/m2 and sub-grain size of about 160nm. The significant increase of the dislocation density was likely due to the severe plastic deformation during FSW. This study provides an insight into understanding the transient behavior of the microstructure under severe thermomechanical deformation.

X-ray and Neutron Diffraction Measurements of Dislocation Density and Subgrain Size in a Friction-Stir-Welded Aluminum Alloy. W.Woo, T.Ungár, Z.Feng, E.Kenik, B.Clausen: Metallurgical and Materials Transactions A, 2010, 41[5], 1210-6