Joint strength evaluation of friction stir welded Al-Cu dissimilar alloys

•Al-Cu joint of dissimilar thickness is successfully obtained using FSW method.•Joint tensile strength of dissimilar metals is examined at different tool offsets.•The joint quality is improved by 1 mm of tool offset along aluminum side.•Joint properties are influenced by the varying intermetallic thickness. Friction stir welding has been successfully employed to fabricate dissimilar thickness AA1050 and oxygen free copper (Cu-OF). The highest value of the joint tensile strength obtained was 91% of the AA1050 alloy strength with the tensile fracture path on the aluminum side. At the Al-Cu interfacial microstructure, a layer of Al4Cu9 and Al2Cu intermetallic compounds (IMCs) with thickness of 2.2 μm–0.26 μm was developed at different welding speeds. The voluminous IMCs have an adverse impact on the tensile characteristics of the joint. The IMCs (0.26 μm−0.77 μm) at welding speeds of 160 mm/min and 213 mm/min with 1 mm tool offset, has trivial effect on the tensile property. The mechanical property of the joint was significantly affected by the tool offset and welding speed. Image processing techniques such as Gaussian blur, histogram normalization and binarisation were utilized to understand the distribution of copper in the weld stir zone.