The static and fatigue strength of laser welded lap joints with different zinc coating weight of steel sheets were quantitatively investigated. The welding phenomenon of zinc coated steel sheet was observed by the laser strobe. From the observation results, the mechanism of the weld defect formation was examined.
The following results have been confirmed:
(1) The quantity of spatters from the weld pool increased with the increase of zinc coating weight of steel sheets.
(2) In the case of steel sheets with zinc coating weight of more than 40 g/m2, 30-40% of the weight of molten metal scattered as spatters.
(3) Blow holes were formed by sputters.
(4) The static and fatigue strength of laser welded lap joints decreased with the increase of zinc coating weight of steel sheets.
(5) The gap width between the sheets suppressed spatters and blow holes.
(6) With regard to the mechanism of spatter formation, the driving force of sputter generation is laser energy, not zinc vaporization, which disturbs the molten metal flow around the keyhole.
