Process parameter influence on defects and tensile properties of friction stir welded T-joints on AA6061-T4 sheets

•T-lap and T-butt joints were fabricated by friction stir welding.•Original joint line with severe deformation (OJLwSD) in T-joints was studied.•Hardness and microstructures in different zones of T-joints were investigated.•Distribution and statistic data length of OJLwSD were analyzed.•Relationships of welding parameters, OJLwSD and properties were studied.

In this study, AA6061-T4 T-joints characterized by combination modes of T-lap and T-butt were fabricated by friction stir welding with different processing parameters. Defects distributed in the obtained specimens were examined by using a stereo microscope and an optical microscope. Process parameter influence on the distribution and the size of original joint line with severe deformation (OJLwSD) defect was investigated. The microstructures and hardness profiles in the T-joints were studied. Influence factors on T-joints’ tensile properties were discussed. In addition, the fracture mode and the fracture surface of the failure samples were observed and discussed as well.