Effects of weld line position and geometry on the formability of laser welded high strength low alloy and dual-phase steel blanks

Abstract

Formability of laser welded blanks (LWBs) was measured in the biaxial stretch forming mode using the limiting dome height (LDH) test. High strength low alloy steel and two dual-phase (DP600 and DP980) steels were used for fabricating LWBs. The failure location and the LDH values of the formed blanks were correlated to the hardness across the welds. The effects of weld line position and geometry on the formality was evaluated by investigating LWBs with three different weld line positions (0, 15 and 30mm offsets from the blank center) for both linear and curvilinear geometry. The formability was found to be dependent on the weld line position and increased when the weld was located farther from the blank center due to more uniform strain developed during LDH tests. Interestingly, weld line geometry was observed to have a stronger influence on the formability DP600 steel. In addition to weld line position and geometry, heat affected zone softening was observed to be the dominant factor in controlling the formability of all the DP980 LWBs and the curvilinear welds of DP600 with failure consistently occurring in the region with more severe softening.