Forming behaviour of friction stir lap welded joints

Friction stir lap welding was performed on two and on three sheets in aluminium alloy, respectively. The effect of the stacking mode of the sheets with different thicknesses and that of the tool probe geometry were analyzed at given rotational and welding velocities. The welding results were studied in the weld joint section perpendicularly to the welding velocity direction. It resulted that, in the case of the stack of three sheets, the thinnest blank has to be positioned in the middle, in order to get a sound weld. In the two sheet stacking, the thinnest blank must be placed below the thickest one. The subsequent upsetting of the lap joint at different temperatures produced an homogeneous microstructure even when the thick tool was used for the friction stir welding. It was observed that low upsetting load values, related to low friction amounts, could determine improved homogenization in terms of microstructure and deformation levels.