The authors have newly developed a LA-GTA (laser-activated Gas Tungsten Arc) welding process, which exerts a drastic effect on the increase in the GTA weld penetration[1-3]. If this technique, which eventually controls the melt flows in the weld molten pool driven by the surface tension gradient, so called Marangoni convection, is applicable to the laser welding process, the laser melting-ability will be efficiently improved. Therefore, laser bead-on-plate welding was performed on the small region produced by the laser-activated process in an oxygen shielding gas to confirm the effect of the pretreatment on the weld penetration. The process was named LA (laser-activated) -^sLaser Welding. In the main result, in the case of laser welding at the low power densities where a thermal conductivity type of welds tend to be obtained, the LA pretreatment rendered the weld penetration deeper. Moreover, in the case of a keyhole type of laser welding at high powers and low speeds, the weld beads with narrow surface widths were stably produced.
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