A three-dimensional numerical model is used to simulate heat transfer and fluid flow phenomena in fiber laser + gas metal arc welding (GMAW) hybrid welding of an aluminum alloy, which incorporates three-phase coupling and is able to depict the keyhole dynamic behavior and formation process of the keyhole-induced porosity. The temperature profiles and fluid flow fields for different arc powers are calculated and the percent porosities of weld beads were also examined under different conditions by X-ray non-destructive testing (NDT). The results showed that the computed results were in agreement with the experimental data. For hybrid welding, with raising arc power, the keyhole-induced porosity was reduced. Besides the solidification rate of the molten pool, the melt flow was also closely related to weld porosity. A relatively steady anti-clockwise vortex caused by arc forces tended to force the bubble to float upwards at the high temperature region close to the welding heat source, which benefits the escape of the gas bubble from the melt pool. When increasing the arc power, the anti-clockwise region was strengthened and the risk of the gas bubble for capture by the liquid/solid interface underneath the keyhole tip was diminished, which resulted in the lower weld percent porosity.

Considering the coupling of a droplet, keyhole, and molten pool, a three-dimensional transient model for the full penetration laser + metal inert gas (MIG) hybrid welding of thin copper alloy plate was established, which is able to simulate the temperature and velocity fields, keyhole behavior, and generation of the welding defect. Based on the experimental and simulation results, the weld formation mechanism for the hybrid butt welding of a 2 mm-thick copper alloy plate was comparatively studied in terms of the fluid dynamic feature of the melt pool. For single laser welding, the dynamic behavior of liquid metal near the rear keyhole wall is complex, and the keyhole has a relatively drastic fluctuation. An obvious spattering phenomenon occurs at the workpiece backside. Meanwhile, the underfill (or undercut) defect is formed at both the top and bottom surfaces of the final weld bead, and the recoil pressure is identified as the main factor. In hybrid welding, a downward fluid flow is strengthened on the rear keyhole wall, and the stability of the keyhole root is enhanced greatly. There are large and small clockwise vortexes emerging in the upper and lower parts of the molten pool, respectively. A relatively stable metal bulge can be produced at the weld pool backside. The formation defects are suppressed effectively, increasing the reliability of full penetration butt welding of the thin copper alloy plate.

Laser–MIG hybrid welding is increasingly used in shipbuilding for medium-thick steel plates, where assembly-induced gaps and misalignment often compromise weld quality. In this study, a three-dimensional transient numerical model is established to simulate the molten pool dynamics during full-penetration laser–MIG hybrid welding of 10CrNiCu steel under varying gaps and misalignment conditions. The model incorporates coupled heat transfer, fluid flow, keyhole behavior, and droplet transfer and is validated against experimental weld profiles. The simulation results reveal that increasing gap size broadens the heat distribution, reduces keyhole depth, and decreases the bridging capacity of the filler metal. Larger misalignment enhances the step effect, promotes gravity-driven downward flow of liquid metal, and increases keyhole instability and porosity risk. The adaptability to assembly errors is further assessed. As welding current increases, the gap tolerance slightly improves from 1.61 mm to 1.65 mm, whereas the misalignment tolerance markedly decreases from 3.00 mm to 1.82 mm due to the earlier onset of porosity defects. These findings provide quantitative guidance for optimizing welding parameters to accommodate realistic assembly variations in marine steel fabrication.

This study employed coaxial laser wire additive manufacturing technology to fabricate Incoloy 825 thin-walled structures and analyzed their microstructure and properties. The results show a gradient distribution of the microstructure along the deposition direction: The microstructure varies significantly along the build direction: the bottom region primarily features columnar and equiaxed grains; the middle zone is mainly composed of coarse cellular dendrites; while the top region shows a mixture of fine equiaxed and cellular grains. Correspondingly, the tensile properties are anisotropic, with the horizontal direction demonstrating superior average tensile strength compared to the vertical direction. The microhardness profile displays a pattern of higher values at both ends and a lower value in the middle. This trend is attributed to grain refinement, which enhances the hardness in the top and bottom regions. The corrosion resistance of the additively manufactured component is slightly lower than that of traditional forgings and is closely related to the microstructural characteristics of each region. This work validates the feasibility of using this technology for forming Incoloy 825 components and provides important experimental insights for the application and process optimization of this material in the field of additive manufacturing.