Optimization of laser welding parameters of high strength DP1200 steel for automotive industry

With the use of ultra-high strength steel sheets in automotive sector structural parts, the welded joints of these steels have gained importance. The laser welding process has several advantages thanks to focusing the high-power laser beam in a narrow area: deep penetration, high strength, obtaining the desired weld geometry, precise and high-quality joining. Achieving the desired level of mechanical properties is possible with the use of appropriate process parameters. In this study, the effects of laser power, scanning speed, laser angle process parameters on weld geometry, microstructure, microhardness, fracture surfaces, and tensile strength were investigated in terms of heat input change in fiber laser welding joints of high-strength DP1200 steels. The experimental design was created for 3 parameters and 5 levels via Central Composite Design and contour and surface graphics were plotted after the tensile test. For maximum shear force objective function, optimum process parameters and parameter affect ratios were determined according to the Response Surface Methodology using the Minitab program, and a mathematical equation was obtained. The laser welding process has recorded with a thermal camera, cooling rates were calculated by analyzing the data. Post-weld stress and displacement values were simulated with the Simufact Welding program. Response Surface Methodology optimum process parameters laser power was 2800 W, scanning speed was 40 mm/s, laser angle was 70ᵒ; the effective parameters were scanning speed, laser angle, and laser power, respectively. It was observed that the grain structure and martensites got thinner with the decreasing heat input, and the grain structure and martensites became coarser with the increasing heat input. High microhardness with high cooling rate were obtained at low heat input; low microhardness values were seen with low cooling rate at high heat input.