Microstructure and mechanical properties of similar and dissimilar laser welds of dp600 and dp1000 steel sheets used in the automotive industry

Abstract

Dual-phase (DP) steel sheets are the most widely used steel group in the automotive industry. When these steel sheets are used in car body components, welding is inevitably needed during the manufacturing process. Although the resistance spot welding (RSW) is the most widely used welding method in the automotive industry, the newly popular laser welding has gained more importance in the welding of these steel grades in recent years. In this work, the DP600 and DP1000 steel sheets were joined as double-sided with the pulsed Nd: YAG (Neodymium-doped Yttrium Aluminum Garnet (Y3Al5O12)) laser welding. Performing similar or dissimilar weld of DP steel sheets is an inevitable demand in the modern automotive industry. So, in this study similar (DP600-DP600, DP1000-DP1000) and dissimilar (DP600-DP1000) steel sheets were welded in the flat position with the butt joint. In order to evaluate welding performance, microstructural studies and mechanical tests were performed, and experiments carried out in this context include optical microscope studies, tensile tests and Vickers microhardness measurements. The tensile strength of the similar welded joints is a little bit lower than the base metals (BM). But, for dissimilar weld, the tensile strength is even lower than DP600-DP600 joint. And the microstructure of the welded joints are composed of martensite, retained austenite and bainite in the fusion zone and a mixture of martensite, bainite, ferrite, retained austenite and tempered martensite in heat affected zone (HAZ).