Formability assessment and failure prediction of laser welded dual phase steel blanks using anisotropic plastic properties

Abstract

Assessment of the role of weld zone and difference in the material properties across the dual phase steel tailor welded blanks (TWBs) during sheet forming is imperative prior to applications in light weight auto-bodies. In the present work, one laser welded blank (LWB) of similar material combination and two different TWBs we're fabricated by laser welding of dual phase steels (DP600, DP980) and interstitial free (IF) steel. The quality of the laser welded similar (DP600-DP600) and dissimilar material (DP600-DP980 and DP600-IF) joints were evaluated in terms of metallographic observations, hardness studies and tensile tests. Evolutions of microstructures within the vicinity of weld region were analyzed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Moreover, the local property changes in the weld regions were observed through micro-hardness and nano-indentation tests. The formability performances of above three welded blanks were evaluated under different deformation modes using three case studies such as Erichsen cupping, deep drawing and double-stage forming tests. It was observed that the formability of DP600 LWBs decreased by 28% due to the presence of weld in comparison to that of the monolithic parent material. In case of TWBs, the weld line movement was observed causing non-uniform deformation and failure at weaker side. The FE models of the above three case studies were developed incorporating Yld2000-2d anisotropy constitutive properties of the parent metal and further considering the properties of the non-homogeneous welded zone. The Marciniak-Kuczynski model and thickness gradient based necking criterion were both applied to predict the failure successfully in the FE model, and the results were validated with experimental data to establish the robustness of both the failure models.