Effect of welding laser process on macrostructures and the mechanical properties of coating steel DP600: Influence of vaporization zinc

This paper presents an analysis of the shear strength evolution of laser welds. DP600 steel sheets, with a thin zinc coating, were welded in a lap joint configuration. With the aim of optimisation, it has been shown that the mechanical set up, i.e. weld gap and clamping force associated with speed and laser power, permit a significant increase in mechanical properties notably in shear strength when the zinc vaporization is optimized. This amelioration required a negative defocusing (−0.33 mm) and a minimal weld gap (0.2 mm) to allow zinc vapour to escape the weld pool and thus avoiding porosity. Equally it has been shown that the shear strength is directly linked to the geometrical properties of the weld bead, particularly at the gap between sheets and principally the control of the zinc vaporization. The relation between welding process parameters, mechanical set up parameters and the nature of the materials have been to control to obtain the best mechanical behaviour.