A novel strengthening method using Al₃Ti for oscillation laser-MIG hybrid welded joints of Al-Zn-Mg-Cu alloy

Al-Zn-Mg-Cu alloys are extensively utilized in lightweight structural applications, with Al-Mg wires commonly employed to mitigate solidification cracking during fusion welding. However, the suboptimal properties of welded joints have remained a persistent challenge, particularly when paired with low-strength wires. Currently, the strength of fusion welded joints in Al-Zn-Mg-Cu alloys typically achieves about 60% of the base material (BM). This study employed an oscillation laser-MIG hybrid welding technique incorporating a titanium interlayer, and the influence of Al₃Ti on microstructural features and mechanical properties was analyzed. Results demonstrated that the mechanical performance of welded joints was significantly enhanced by the presence of Al₃Ti. Numerical simulations indicated that oscillation laser-induced stirring improved melt fluidity in the molten pool, leading to the formation and uniform distribution of Al₃Ti throughout the weld. Al₃Ti particles as nucleation substrates, facilitating grain refinement. A strengthening mechanism for Al₃Ti applicable to fusion welded joints in Al-Zn-Mg-Cu alloys was proposed, incorporating grain boundary strengthening and particle strengthening. The tensile strength and elongation of the welded joints increased to 401.74 MPa (71% of BM) and 7.27%, respectively. This work demonstrated an innovative processing and an unconventional reinforcement phase which provided guidance for fusion welding of high-strength aluminum alloys in practical applications.