Experiment-based regional characterization of HAZ mechanical properties for laser welding

Abstract

As for the tailor welded blanks (TWB) of dual-phase steels, heat-affected zone (HAZ) always exhibits significant changes of mechanical properties after experiencing the laser welding process. Hence, the characterization of HAZ mechanical properties is very critical for the accurate forming simulation and service performance of laser-welded blanks. However, it is still difficult to obtain the regional mechanical properties of HAZ because it has a varied transition of microstructures and mechanical properties in a very narrow range (e.g., <1 mm). In this paper, to investigate the regional mechanical properties of HAZ in the laser-welded joints of DP600 steels, an experimental approach was carried out based on the thermal simulation running on the Gleeble machine. The thermal histories of different regions in HAZ during laser welding were simultaneously measured by thermocouples, and then applied for the thermal simulation. The regional characterization of HAZ mechanical properties was realized with the thermal-simulated HAZ specimens. The results show that the thermal histories in weld and HAZ are very sensitive to the distance from the weld centerline, which results in different relevant microstructures and mechanical properties. The tensile strength of HAZ at different locations decreases with increasing distance from the weld centerline, but the elongation has the opposite tendency. The regional mechanical properties of HAZ were also applied to the finite element model of the tensile testing for welded joint by ABAQUS, an elastic-plastic finite element code. And the finite element simulation shows good agreement with the experimental.