Experimental investigation of the mechanical response of laser-welded dissimilar blanks from advanced- and ultra-high-strength steels

Abstract

We report experimental results on the mechanical response of dissimilar tailor-welded blanks (TWB) from an advanced- and an ultra-high-strength steel for automotive applications. These are the dual-phase steels DP 780 and DP 1180, respectively. First, we present the tensile and anisotropic properties of the two base-materials. During testing, the full-fields of strain and temperature are acquired, using the Digital Image Correlation (DIC) and Infrared Thermography (IR) techniques. The latter is critical, since both materials are prone to deformation-induced heating, which establishes a temperature gradient along the test-section, and which in turn limits the ductility observed. We then describe the laser-welding apparatus, and microstructural observations and measurements around the weld-seam. Subsequently, we test tensile coupons from the TWBs, with the weld-seam oriented transversely, 45° and parallel to the longitudinal direction of the loading. We detail the failure modes and the macroscopic load–displacement responses. Furthermore, with the aid of the DIC and IR images, we probe the local strain and temperature fields and their evolution, and correlate these to the overall response and failure of the TWB tensile coupons.