Improving formability of laser welded automotive dual phase steels with local cooling

Abstract

A new laser welding process with the local cooling was presented and applied to two automotive dual phase steels, DP780 and DP980. The microstructure, microhardness, tensile properties of welded joints and limiting dome height (LDH) of welded blanks were investigated. It is observed that the local cooling during laser welding process can greatly reduce the martensite tempering and thus reduce the heat affected zone softening. The laser welded joints with the local cooling all failed at the base metal, and exhibit the comparable strength and ductility with the base metal. For the welded blanks with the local cooling, LDH is increased significantly, and failure initiates from the weld and propagates perpendicular to the weld.