Laser brazing technology for Zn-coated steels with a copper alloy wire has received considerable attention because of its many advantages such as good mechanical properties, higher solubility of zinc, improved gap tolerance in automotive industries. However, defects such as pits and pores are sometimes found in laser-brazed beads, and their formation mechanism is not elucidated.
In this study, therefore, YAG laser brazing was carried out on galvanized steel sheets using a copper alloy wire under various conditions with the objectives of elucidating brazing phenomena, pit formation mechanism and the effect of brazing conditions on joint properties. The formation conditions of sound brazed beads and defects were confirmed by investigating the kind of a filler wire, the effect of the distance between a laser beam axis and a wire target, brazed volume, traveling speed, brazing directions and laser-defocused distance on the bead appearance and pits or porosity formation. Laser brazing phenomena and pit formation mechanism were elucidated by observing droplets transfer from a copper alloy wire, molten pool behavior, evaporation of zinc, and bubble formation and flow with a high-speed video camera and X-ray transmission real-time observation method.