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.

This paper investigated the Mg-rich phase precipitation behavior and the corrosion performance throughout the thickness direction within the stirred zone (SZ) of friction stir welded (FSW) AA5083 alloy after 175 °C/100 h sensitization. For the as-welded SZ, the recrystallized grain size gradually decreased from the top surface (5.5 μm) to the bottom (3.7 μm). The top and bottom of the SZ maintained relatively high levels of deformed grains and accumulated strain induced by either shoulder pressing or pin stirring. After 175 °C/100 h sensitization, 100 nm thick β′-Al₃Mg₂ precipitates were present along the grain boundaries (GBs) in the SZ. The bottom of the SZ exhibited more continuous precipitates along GBs due to the fine grain size and the large fraction of high-angle grain boundaries (0.724%). Although the as-welded SZ exhibited excellent corrosion resistance, it became extremely vulnerable to intergranular cracking (IGC) and stress corrosion cracking (SCC) after sensitization. The large SCC susceptibility indices of the SZ samples ranged from 66.9% to 73.1%. These findings suggest that sensitization can strongly deteriorate the corrosion resistance of the Al-Mg FSW joint, which is of critical importance for the safety and reliability of marine applications.

Connecting small pieces of parts manufactured by Selective Laser Melting (SLM) and traditional formed parts into large structural component by using welding technology provides a high-efficiency and low-cost way for expanding additive manufacturing technology. SLMed parts usually exhibit similar or superior tensile strength but lower ductility compared to that of cast or rolled ones due to the rapid cooling and cyclic heating deposition characteristics. What about the weldability of the dissimilar joints of SLMed parts and rolled ones? Whether the properties of the welded joints can be improved by heat treatment under the premise of ensuring the reliability of the joint is unclear. The weldability and the effect of heat treatment temperature on the microstructure and properties of laser-welded joints of SLM-316 L/rolled-316 L are studied in this article. The results show that the joints exhibit good weldability without obvious defects. The low temperature annealing treatment had no significant effect on the multilayered structure and columnar austenite grains, but only changed the morphology and content of ferrite within the grains leading to the slight increase of elongation but decrease of material strength. The corrosion performance was almost unaffected. After solution annealing above 1,000°C, the ferrite was nearly dissolved in the austenite matrix. The austenite recrystallized and the multilayered structure was destroyed, which resulted in decrease of material strength, a slightly improvement in corrosion resistance, and the elongation was greatly enhanced. After the detailed study, it was concluded that the post-weld heat treatment provided an effective way for improving the overall performance of the SLM-316 L/rolled-316 L dissimilar joint.

Hybrid laser-double-arc welding (HLDAW) is an efficient welding method with multi-heat sources comprised of two arcs and a laser beam, which is an intricate process with much randomness and uncertainty due to the mutual effect between multi-plasmas. Compared with double-arc welding (DAW), HLDAW can generally obtain a more stable welding process and deeper weld penetration, which is directly affected by the synergistic effect of multiple heat sources; however, the mechanism has not been systematically studied. In this study, the multi-information analysis method is adopted to study the distribution of electron temperatures, electron densities and electrical conductivity of double-arc welding (DAW) and HLDAW by utilizing synchronous radiation spectrum, high-speed photography and electrical signal sensing technology. The results indicated that the high concentration of charged particles provided a conductive channel for the two arcs to achieve a more stable welding process in HLDAW. The synergy between the laser and the arc changed the flow mode of the weld pool, which facilitated the molten metal flowing toward the bottom of the molten pool. Obtaining the same melting depth, the line energy input of HLDAW was 13% lower than that of DAW; the heat affected zone is narrower and the grain size is smaller. The weld penetration depth was improved in HLDAW, which was 1.8 times that of DAW and 1.5 times that of pure laser welding under the laser power of 1.5 kW. The weld penetration of HLDAW increased with laser power.