Impact Mechanism of Multiple Major Welding Parameters on Mechanical Properties of Laser Brazing Lap Joint of Galvanized Steel for Vehicle

In order to research the effect of process parameters (laser power, welding speed, wire-feed speed, spot diameter) on mechanical properties of Zn-coated Steel Laser Brazing Lap Joint for vehicle, the influence of welding parameters on energy input of brazing seam cross section was theoretically analyzed, and then a great number of laser brazing experiments of 0.7mm galvanized steel was carried out. After that, the tensile strength and micro-hardness tests were also done for well-formed joints of galvanized steel formed in the laser brazing. The results show that joints with good mechanical properties and surface morphology can be formed when laser power is in the range of 2500-3200W and the other parameters keep in a specified range. Joint performance significantly reduces when the value of wire-feed speed exceeds 3.0m/min for that a wider brazing seam cross section can’t be formed. And tensile strength of the joint drops steeply when welding speed exceeds 50mm/s, because the solid-liquid surface tension between the brazing filler metal and the base metal increases. When the spot diameter increases within the appropriate range, the decrease of the energy density slows down the cooling rate of the brazing filler metal, which makes the mechanical properties of the brazing seam maintain a good condition. Moreover, under the same welding parameters, the micro-hardness anywhere inside the weld joint is uniform, which testifies the mechanical performance of the brazing seam is safe and stable.