Study on laser welding of Cu/Ti dissimilar materials using a hybrid light source with wavelengths of 455/1080 nm

The utilization of near-infrared lasers (approximately 1000 nm wavelength) on non-ferrous metals often presents challenges like unstable weld pools, suboptimal weld formation, and reduced mechanical performance due to high reflectivity. This investigation focused on dissimilar Cu/Ti materials undergoing coaxial welding with a near-infrared fiber laser (λ = 1080 nm) and a blue diode laser (λ = 455 nm) at various power ratios. The study centered on analyzing molten pool characteristics, microstructure, and mechanical properties of weld. The combination 1080/455 nm wavelength of lasers expanded the heating range along the weld seam, enhancing Keyhole stability and dynamic stability of molten pool. Increasing the power ratio of the 455 nm wavelength laser reduced temperature gradients in the molten pool, resulting in superior-quality joint with a maximum tensile strength of 245.93 MPa, surpassing that of the Cu base material. Interface analysis revealed that, while there was no significant variance in the phase composition of the Ti-side, augmenting the power ratio of the 455 nm wavelength laser increased post-heating during welding process, reducing low-angle grain boundaries in the Ti-side fusion zone from 58.3 % to 48.3 %. This enhanced distribution patterns for low-angle grain boundaries and geometrically necessary dislocations, optimizing stress distribution. The absorption of 455 nm wavelength laser energy by Cu results in molten pools that spread towards the Cu-side regions. This process causes a change in composition from TiCu2 to TiCu4 in the fusion area, aided by exceptional thermal conductivity, resulting in increased cooling rates and undercooling levels. This grain refinement improved resistance against dislocation generation, enhancing strength and plasticity. This study demonstrates the feasibility of achieving high-quality welding between Cu/Ti dissimilar materials using a coaxial hybrid beam with a wavelength of λ = 1080/455 nm, offering an innovative solution for laser welding of highly reflective materials.