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Weld initiation experiments were undertaken on various Al-Mg(-Si) alloy extrusions to develop fixed-gap bobbin tool designs and process procedures to facilitate friction stir welding (FSW) of sheet specimens as thin as 3 mm. The alloy grades studied were AA 5083-H111, AA 5454-H111 and AA 6061-T6 with material thicknesses of 3-5 mm. Welding was performed using a low-cost FSW system, incorporating pneumatically and electrically actuated rollers to guide and drive workpiece materials through the machine. The design features of fixed-gap bobbin tools were studied with respect to scroll features and counter-bore diameter and depth. Weld initiation reliability was considered in relation to workpiece factors (e.g. material product form, joint gap, workpiece edge misalignment and heat-softened material effects) and process procedure factors (initial travel speed and spindle speed, tool surface condition and fixture rigidity). Welding parameters for fabricating full-length welds were determined and weldments were characterised by microstructure observations and tensile tests.

9th International Symposium, 15-17 May 2012, Session 7A: Variants II, Paper 01