Gap tolerance and molten pool destabilization mechanism in oscillating laser-arc hybrid welding of aluminum alloys

Abstract

Oscillating laser-arc hybrid welding (O-LAHW) offers significant advantages in enhancing efficiency and mechanical properties. However, in actual production, gap fluctuations can cause instability, limiting its application in large-scale structure manufacturing. In this study, we explored the impact of gap fluctuation on the destabilization of the molten pool in aluminum alloy O-LAHW and identified the maximum gap tolerance for various conditions. High-speed photography revealed that the oscillating molten pool undergoes a transitional state of periodic collapse before complete instability, a behavior distinct from that of a non-oscillating molten pool. We also analyzed the variations in weld geometry prior to destabilization and developed a global force model of the molten pool to identify key geometrical parameters and related driving forces contributing to destabilization. The results show that maintaining a surface tension ratio of over 55 % at the root of the molten pool is crucial for its stability. Additionally, the effects of oscillatory behavior and gap variations on the laser-substrate interaction were explored, revealing the physical mechanisms behind the changes in key geometrical parameters of the melt pool cross-section. The centrifugal effect generated by high-frequency oscillation is identified as a crucial mechanism for extending the duration of periodic collapse compared to non-oscillating molten pools. By discussing the interactions between energy absorption, molten pool shape, and molten pool forces, the study reveals the evolution process of weld destabilization and explains the differences in gap tolerance between oscillating and non-oscillating laser-arc hybrid welding, providing a reference for improving weld stability.