Formability Analysis of Diode-Laser-Welded Tailored Blanks of Advanced High-Strength Steel Sheets

Abstract

Currently, advances due to tailored blanking can be enhanced by the development of new grades of advanced high-strength steels (HSSs), for the further weight reduction and structural improvement of automotive components. In the present work, diode laser welds of three different grades of advanced high-strength dual-phase (DP) steel sheets (with tensile strengths of 980, 800, and 450 MPa) to high-strength low-alloy (HSLA) material were fabricated by applying the proper welding parameters. Formability in terms of Hecker's limiting dome height (LDH), the strain distribution on the hemispherical dome surface, the weld line movement during deformation, and the load-bearing capacity during the stretch forming of these different laser-welded blanks were compared. Finite element (FE) analysis of the LDH tests of both the parent metals and laser-welded blanks was done using the commercially available software package LS-DYNA (Livermore Software Technology Corporation, Livermore, CA); the results compared well with the experimental data. It was also found that the LDH was not affected by the soft zone or weld zone properties; it decreased, however, with an increase in a nondimensional parameter, the ''strength ratio'' (SR). The weld line movement during stretch forming is an indication of nonuniform deformation resulting in a decrease in the LDH. In all the dissimilar weldments, fracture took place on the HSLA side, but the fracture location shifted to near the weld line (at the pole) in tailor-welded blanks (TWBs) of a higher strength ratio.

Use of High-Power Diode Laser Arrays for Pre- and Post-Weld Heating during Friction Stir Welding of Steels

“…The changes in absorptivity of metals due to variance in irradiance, wavelength, polarization, and angle of incidence as well as due to variance in material properties such as composition, surface roughness, oxide layers, and contamination are beyond the scope of this review, but these aspects as well as the performance of HPDLs on different metals including aluminum, titanium, and steels are discussed in other work by the authors [28]. For the previous reasons HPDL systems have been used for laser assisted machining and laser surface heat treatment for a variety of steels [29][30][31][32]; however, the majority of these applications involve rapid heating of steels into the austenite region followed by rapid cooling to form martensite resulting in improved hardness of selected regions of the workpiece. In the proposed application, a HPDL would be used to heat the workpiece (ideally below the austenite region) immediately prior to FSW such that the stir zone (SZ) is preheated and softened resulting in reduced tool wear and overall less heat input from the FSW process.…”

Use of the Aging Effect to Change the Local Properties of Structure Components

“…Their high yield and tensile strengths enable a decrease in sheet thickness (weight saving) and, at the same time, maintaining or even improving crash behavior (safety) [1][2][3][4]. This is achieved by micro-alloying [5] and a thermo-mechanical treatment [6].…”

Local Laser Heat Treatment in Dual-Phase Steels

“…Their high yield and tensile strengths enable a decrease in sheet thickness (weight saving) and, at the same time, maintenance or even improvement of crash behavior (safety). [1][2][3][4] This is achieved by microalloying [5] and a thermomechanical treatment. [6] These AHSS steels, which are mostly multiphase steels, are characterized by good formability, high strength, and a bake hardening (BH) effect.…”