Abstract:

In this study, the DP600 and DP1000 steel sheets were joined with the pulsed Nd: YAG (Neodymium-doped Yttrium Aluminum Garnet (Y3Al5O12)) laser welding and, mechanical and microstructure properties of the dissimilar welds were experimentally investigated. As known, there is a demand in modern automotive industry for performing dissimilar weld of DP steel sheets. In the laser welding operation, the selection of welding parameters affects the final properties of welds substantially. So, the main aim of this study was determining the influence of pulse frequency on the mechanical properties of pulsed Nd:YAG laser welded DP600-DP1000 steel sheet joints. For this purpose, dissimilar (DP600-DP1000) steel sheets were double-sided welded with the butt joint. To analyze the welding performance, microstructural studies, tensile tests and microhardness measurements were carried out. The weld cross-sections of the joints revealed three main distinct macrostructural zones: Base metal and heat affected zone of both steels, and fusion zone. Moreover, a transition zone was observed between the base metal and heat affected zone on the DP1000 sides. Higher pulse frequency led to deeper penetration and larger fusion zone and heat affected zone. The joints welded without any filler wires had macro porosities in the fusion zones. The tensile properties of the joints significantly increased with increasing pulse frequency. The tensile properties obtained in this study may be quite satisfactory for automotive industrial applications. Fusion zone had the highest microhardness values. However, the lowest microhardness values were observed in the transition zone on DP1000 side. 

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