Novel technique for laser lap welding of zinc coated sheet steels

When zinc coated steels are laser welded, zinc adjacent to the weld bead is vaporized and will cause serious weld pool disruption in lap welding unless special measures are applied such as provision of a joint gap for vapor venting. A novel alternative technique has been developed to stabilize laser lap welding: this involves addition of a small amount of aluminum to the faying surface region, so that a liquid Al–Zn alloy of high boiling point is formed, thus lowering the Zn vapor pressure. Lap welds have been made with good process stability using Nd: yttrium–aluminum–garnet and direct diode lasers, and with added Al in the form of inserted foil or previously applied cold sprayed coatings. The development is described in U.S. Patent Application No. 11/226,834. Process optimization is currently under way to define optimum aluminum addition rates that will reliably suppress defects while minimizing Al uptake into the steel weld pool.