Effect of tool pin insertion depth on friction stir lap welding of aluminum to stainless steel

Aluminum (1060Al) and stainless steel (SUS321, austenitic) were friction stir lap welded using a stir tool consisting of a cutting pin and a concave shoulder. Two welding processes characterized by plunge depth of the pin were designed. In process 1, the pin remains inside the Al metal and the pin tip approaches the stainless steel surface, while in process 2, the pin tip penetrates through the Al metal and was inserted into the stainless steel to generate a machining process. Morphological and compositional characterization of the joint revealed defect-free joining at the interface with a visible mixed layer corresponding to the possible phase FeAl₃ and the solution of Fe in Al, resulting in high tensile strength of up to 89 MPa in process 2, while in process 1, the tensile strength was up to 71 MPa.