Processing and banding in AA2524 and AA2024 friction stir welding

An attempt has been made to clarify the relationship between the periodicity of process parameters and that of the micro-/mesostructural banding in friction stir welding (FSW). The oscillation of FSW parameters was measured and analysed during baseline experiments without welding and during a series of FSW of AA2524 and AA2024 aluminium alloys; the banded structures in all the welds were also characterised. It is found that independent of the tool runout, there are well defined periodic variations in the process forces, the translational resistance force F-x) and Z axis force F-z of the welding tool in all joints. The measured band spacing is closely correlated with the oscillation period of process forces F-x and F-z, exerted on and by the welding tool. The direct and consistent relationship observed between periodicity in variation of F-x and F-z and the metallurgical structure, e. g. grain size, particle distribution, band width and microhardness, indicate that the formation of banded structures in FSW joints is related to the periodic variation of welding parameters.