Weld Defect Prevention for Fillet Welded Joints on Steel Plates Coated with Shop Primer using Hot-wire Laser Welding

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Shop primer is a predominant cause of pits and blowholes during fillet welding using a conventional CO₂ arc welding process. The hot-wire laser welding process for fillet welds employs a reflected laser beam incident on a molten pool for melting the base metal, and produces a weld bead with an extremely low dilution of base metal. In this study, weld-defect prevention in hot-wire laser welding as applied to steel plates coated with shop primer was investigated by examining the vaporization of the shop primer at the molten pool front and beneath the stiffener at the root region. A melting technique employing a reflected laser beam incident on the molten pool surface can efficiently remove the shop primer at the molten pool front during welding. The quantity of several gases and metallic vapors emitted during decomposition of the shop primer at a root was reduced markedly during hot-wire laser welding under extremely low base metal dilution. The above features of the hot-wire laser welding process achieved sound fillet welds without pits and blowholes.