Effect of weld bead property on formability of laser welded joint

Abstract

Laser welding is applied to joining blank sheets for car body parts in automotive products. With this technology, the formability of the laser welded joint is important because laser welding produces very hard and brittle weld beads on steel sheets which have high formability.In this research, several kinds of ultra-low carbon and low carbon steel sheets (thickness: 0.70-0.8mm, tensile strength: 290-445MPa) used in car body parts were butt-welded with a CO2 laser under various welding conditions to change the weld metal chemistry and bead shape. After welding, the weld bead width and weld metal hardness were measured. The strength and formability of the welded joint were estimated by the tensile test and Erichsen test.The higher tensile strength steel gave a harder weld metal because of higher contents of alloying elements. The hardness of the weld metal hardly affected the tensile property of the welded joint. Welded joints with harder weld metal, however, showed lower Erichsen values. This problem should be improved by feeding a suitable filler wire into the molten metal.Weld bead width also affected the formability of welded joints. Welded joints with wide beads showed low Erichsen values. Thus, the formability of laser welded joints was strongly dependent on weld bead properties such as hardness and bead width.Laser welding is applied to joining blank sheets for car body parts in automotive products. With this technology, the formability of the laser welded joint is important because laser welding produces very hard and brittle weld beads on steel sheets which have high formability.In this research, several kinds of ultra-low carbon and low carbon steel sheets (thickness: 0.70-0.8mm, tensile strength: 290-445MPa) used in car body parts were butt-welded with a CO2 laser under various welding conditions to change the weld metal chemistry and bead shape. After welding, the weld bead width and weld metal hardness were measured. The strength and formability of the welded joint were estimated by the tensile test and Erichsen test.The higher tensile strength steel gave a harder weld metal because of higher contents of alloying elements. The hardness of the weld metal hardly affected the tensile property of the welded joint. Welded joints with harder weld metal, however, showed lower Erichsen values. This problem shoul...