Papers by Keyword: Primer-Coated Steel

Abstract: This study examines for keyhole behavior by observing the laser-induced plasma and investigates the relation between keyhole behavior and formation of weld defect. Laser-induced plasma has been accompanied with the vaporizing pressure of zinc ejecting from keyhole to surface of primer coated plate. This dynamic behavior of plasma was very unstable and it was closely related to the unstable motion of keyhole during laser welding. As a result of observing the composition of porosity, much of Zn element was found from inner surface of it. But Zn was not found from the dimple structure fractured at the weld metal. therefore we can prove that the major cause of porosity is the vaporization of primer in lap position. Mechanism of porosity-formation is that the primer vaporized from the lap position accelerates dynamic behavior of the key hole and the bubble separated from the key hole is trapped in the solidification boundary and remains as porosity.

Abstract: The application of laser welding technology has been considered to shipbuilding structure. However, when this technology is applied to primer-coated steel, good quality weld beads are not easily obtained. Because the primer-coated layer caused the spatter, humping bead and porosity which are main part of the welding defect attributed to the powerful vaporizing pressure of zinc. So we performed experiment with objectives of understanding spatter and porosity formation mechanism and producing sound weld beads in 6
t primer coated steels by a CO2 CW laser. The effects of welding parameters; defocused distance, welding speed, coated thickness and coated position; were investigated in the bead shape and penetration depth on bead and lap welding. Alternative idea was suggested to suspend the welding defect by giving a reasonable gap clearance for primer coated thickness. The zinc of primer has a boiling point that is lower than melting point of steel. Zinc vapor builds up at the interface between the two sheets and this tends to deteriorate the quality of the weld by ejecting weld material from lap position or leaving porosity. Significant effects of primer coated position were lap side rather than surface. Therefore introducing a small gap clearance in the lap position, the zinc vapor could escape through it and sound weld beads can be acquired. In conclusion, formation and suspension mechanism of the welding defects was suggested by controlling the factors.