Joining of Al 5052 Alloy to Advanced High-Strength Steel Sheets of Dissimilar Thickness Using Laser-Assisted Friction Stir Welding

Multi-material mixed structures (MMMS) are becoming increasingly important to meet the demand for lightweighting in the automotive industry. In this study, the joining of 2.5 mm thick Al 5052 alloy and 1.4 mm thick DP 590 steel sheets was conducted using laser-assisted friction stir welding (LAFSW). A parametric study varying rotational and travel speeds was performed to investigate the effects of process parameters on tensile strength and axial force. The highest tensile strength obtained for the LAFS welds was 193 MPa, which corresponds to approximately 88% of the tensile strength of the Al base metal. The axial force during welding was lower than that of conventional friction stir welding (FSW) due to the thermal softening induced by laser preheating. An intermetallic compound (IMC) layer with a thickness of approximately 5 μm was observed at the joint interface. X-ray diffraction (XRD) analysis of the Fe/Al interface indicated that the IMC layer was composed of FeAl, Fe2Al5, and Fe4Al13. Furthermore, minute fragments of IMCs and steel particles dispersed in the nugget zone contributed to the joint strength by acting as reinforcements within the Al matrix. These results suggest that the LAFSW process is an effective alternative to FSW for Al/steel dissimilar joining.