CO2 laser welding of galvanized steel sheets using vent holes

Joining of galvanized steels is a challenging issue in the automotive industry because of the vaporization of zinc at 906 degrees C during fusion welding of steel (> 1530 degrees C). In this work, hot-dip galvanized steel sheets of 0.68 mm thick (24-gage) were pre-drilled using a pulsed Nd:YAG laser to form vent holes along the weld line and then seam welded in the lap-joint configuration using a continuous wave CO2 laser. The welds were evaluated through optical and scanning electron microscopy and tensile/hardness tests. The vent holes allowed zinc vapors to escape through the weld zone without causing expulsion of molten metal, thereby eliminating the defects such as porosity, spatter, and loss of penetration. In addition, riveting of welds occurred so long as the weld width Was greater than the hole diameter that in turn provided much higher strength over the traditional "joint gap" method. (C) 2008 Elsevier Ltd. All rights reserved.