Obtaining high formability of IF-galvanized steel tailor welded blanks by applying optimum CO2 laser welding parameters

Tailor welded blanks are complex component designs tailor-made through welding of multiple metal sheets with different thicknesses, shapes and/or strengths prior to forming. Making tailor welded blanks out of interstitial free galvanized steels not only provides the general advantages of tailor blanks including the weight and manufacturing cost reductions per part, but also considering the properties of the parent sheet, could guarantee exceptional corrosion resistance as well as favorable formability characteristics. The quality of the weld joint in these blanks and their formability is directly influenced by the parameters of the welding process. In this research, the use of CO2 laser for welding thin interstitial free galvanized steel sheets with different thicknesses (0.8 and 1.2 mm) was optimized using the Taguchi analytical methodology. The welding parameters including the shielding gas pressure, laser power and travel speed of the laser beam were evaluated by measuring the dome height value after forming and the optimal welding parameters values were obtained. The optimal result was equated with the highest dome height value and consequently highest formability. Results showed that the welding parameters have a great effect on achievable properties of tailor welded blanks and entrapment of zinc vapor due to evaporation of zinc has a significant role in determining the weld quality of the studied blanks. Microstructure, hardness and mechanical properties of different welds were also investigated. Formation of voids and porosity as well as lack of diffusion were some of the results of welding with non-optimized parameters. An equation based on a regression model is presented to predict the minimum dome height value of tailor welded blank consisted of interstitial free galvanized steels with a thickness ratio of 1.5.