Investigation of joint shapes for friction welding between 7075-T6 Al alloy and low carbon steel with an insert metal of pure Ti

• Friction welded joint strength of AA7075 and low carbon steel (LCS) was investigated. • Joints were made in a single-step process using pure Ti (CP-Ti) as an insert metal. • AA7075 flash cracking could prevent with larger AA7075 weld diameter than CP-Ti side. • Suitable CP-Ti insert metal shape was also suggested for obtaining good joints. • AA7075 and LCS could be simultaneously friction welded by using CP-Ti insert metal. Direct friction welding between type 7075-T6 aluminum alloy (AA7075) and low carbon steel (LCS) is particularly difficult, as cracking often form in the AA7075 flash and propagate to the weld interface during the welding process. This study investigated the simultaneous friction welding of AA7075 and LCS using commercially pure titanium (CP-Ti) as an insert metal in a single-step process, with the aim of achieving a joint free of cracks into the AA7075 flash. The joint free of cracks into the AA7075 flash was not obtained by varying of only the shape of the CP-Ti insert metal. However, flash cracking could be prevented when the weld diameter of the AA7075 side was larger than that diameter of the CP-Ti insert metal, and used with a suitable shape of CP-Ti insert metal having the groove to the AA7075 side. Furthermore, the joint having high tensile strength exceeding the yield strength of the LCS base metal was achieved; specifically, a forge pressure of 400 MPa resulted in approximately 83% of the tensile strength of the LCS base metal. Despite these improvements, the good joint such as fracture occurring within the LCS base metal could not be realized, since the adjacent region of the LCS side is not much deformed even if the joint is made with high forge pressure. Hence, further optimization of the CP-Ti insert metal shape is essential to promote greater deformation of the LCS side and enhance overall joint characteristics.