Influence of tool plunge depth and welding distance on friction stir lap welding of AA5454-O aluminum alloy plates with different thicknesses

AA5454-O aluminum alloy plates with thicknesses of 1.4 and 1.0 mm were friction-stir-lap-welded (FSLWed). The influences of the tool plunge depth and welding distance on surface appearance, macrostructure and mechanical properties of the FSLWed plates were experimentally investigated. The tensile shear load of the FSLWed plates was compared with that of the adhesive-bonded plates. Defect-free FSLWed zones were successfully obtained in all the tool plunge depths and the welding distances. The FSLWed zones exhibited the relatively smooth surface morphologies. Under all the FSLWed conditions, the FSLWed zone exhibited higher average hardness than the base metal. In addition, the upper plate exhibited a higher average hardness than the lower plate, although there was no special tendency in spite of the change in the tool plunge depth and the welding distance. The maximum tensile shear load of the FSLWed plates was much higher than that of the adhesive-bonded aluminum alloy plate. Especially, under the FSLW condition of the plunge depth of 1.8 mm and the welding distance of 40 mm, the tensile shear load of the FSLWed plate reached a level about 41% greater than that of the adhesive-bonded aluminum alloy plate. In addition, the maximum tensile shear load of the FSLWed plate was increased with the increase of the welding distance.