Optimizing the shoulder diameter for double side friction stir welding of medium-thick TC4/AA2024 dissimilar alloys by Taguchi optimization technique

Titanium alloy and aluminum alloy have a wide range of applications in industry; the welded Ti/Al composite structure can realize the complementary advantages of the two materials and has great potential for applications. Double side friction stir welding (DS-FSW) was used to join 8-mm-thick TC4 titanium alloy and 2024-T4 aluminum alloy. The welding parameters were optimized by the Taguchi optimization technique and the effect of the tool shoulder diameter on the microstructure and mechanical properties of the Ti/Al joint was systematically studied. It revealed that the rotation speed and shoulder diameter play a vital role in maximizing the tensile properties for the medium-thick TC4/AA2024 DS-FSW joints within the range of welding parameters studied, while the welding speed has relatively little influence. The results show that the joints are prone to crack during DS-FSW when a tool with a relatively large shoulder diameter is employed. While a smaller tool shoulder is beneficial to form thinner intermetallic compound layers (IMCs) at the Ti/Al interfaces, resulting in better mechanical properties of the joint. The maximum tensile strength of the joint is 228 MPa, which is achieved at the rotation speed of 400 rpm and the welding speed of 40 mm/min for the tool shoulder diameter is 11 mm, while the maximum tensile strength of the joint is only 122 MPa under the same welding parameters when the diameter of the tool shoulder is 15 mm.