Tandem laser-gas metal arc welding joining of 20 mm thick super duplex stainless steel: An experimental and numerical study

The present work covers the topic of strains and stresses prediction in case of welded steel structures. Steel sheets of 20 mm thickness made in UR™2507Cu are welded using a laser and gas metal arc welding processes combination. The focused laser beam leads the arc in a Y-shape chamfer geometry. Both sources are 20 mm apart from each other in order to avoid any synergic effect with each other. In order to predict residual strain, a 3D unsteady numerical simulation has been developed in COMSOL finite element software. A volume heat source has been identified based on the temperature measurements made by 10 K-type thermocouples, implanted inside the workpiece. The 50 mm deep holes are drilled in the workpiece using dye-sinking Electrical Discharge Machining (EDM) machine. Before the implantation in the hole, each thermocouple is surrounded by Inconel sheathing. Hot junctions of the thermocouples are positioned in a way to feel two advancing molten pools. The equivalent heat source is composed of three sources. First one is a Goldak source that represents the molten pool induced by gas metal arc welding. The second one is a cylinder with an elliptic cross-section that represents the focused laser beam penetrating into the workpiece. The third one is a surface Gaussian source that represents energy radiated by arc and blocked by workpiece surface. Concerning mechanical simulation, an elasto-plastic behavior with isotropic hardening is implemented. A weak coupling is established between equations governing heat transfer and mechanics thanks to the temperature dependent coefficient of linear expansion. This numerical simulation made with some simplifying assumptions predicts an angular distortion and a longitudinal shrinkage of the welded structure. The numerical results are consistent with the displacements measured by digital image correlation method

The numerical challenges in multiphysical modeling of laser welding with arbitrary Lagrangian-Eulerian method

International audienceThe interaction of high power laser beam with metallic materials produces a number of interconnected phenomena that represent a serious challenge for numerical modeling, especially for creation of auto-consistent models. Additional difficulty consists in lack of data on materials properties at the temperatures superior to their melting point. The present work summarizes the numerical challenges in creation and validation of free-surface models using ALE moving mesh coupled with heat transfer equation and Navier-Stokes fluid flow

The Numerical Challenges in Multiphysical Modeling of Laser Welding with ALE

International audienc

La compréhension et la maîtrise des jonctions hétérogènes titane-aluminium réalisés par faisceau laser

La présente étude est dédiée à la compréhension des facteurs influençant la résistance mécanique d’un assemblage entre l’alliage de titane Ti6Al4V avec l’alliage d’aluminium AA5754 par faisceau laser Yb:YAG. Le plan d’expériences proposé a permis de mettre en évidence les effets des paramètres opératoires sur la composition et la morphologie de la zone fondue ainsi que l’identification des conditions opératoires les plus favorables. L’étude numérique multiphysique basée sur l’utilisation de la méthode des éléments finis prenant en compte les transferts de chaleur, la mécanique des fluides et le transport des espèces, a démontré les conséquences des différences de propriétés thermo-physiques des matériaux à assembler, sur la création de la liaison ainsi que le rôle des mouvements du liquide dans la formation d’une zone riche en phases intermétalliques

Use of pure vanadium and niobium/copper inserts for laser welding of titanium to stainless steel

International audienceNiobium and vanadium have high metallurgical compatibility with titanium and therefore can be used as inserts to avoid the accumulation of brittle intermetallic phases such as Fe2Ti during the fusion welding of titanium alloys with steels. In the present study, the continuous double pass welding of 1 mm thick Ti-6Al-4V alloy and 316 L stainless steel plates through several mm wide pure vanadium or niobium insert was studied. In case of a vanadium insert, a beam offset on the vanadium was found to produce cold crack formation in vanadium/316 L melted zones containing more than 40 wt.% V despite the absence of σ phase. Whereas a centered beam position and offset on the steel side produced crack-free melted zones still composed of (Fe, V) solid solutions, and exhibiting a ductile fracture in the unmelted vanadium insert at UTS of 493 ± 25 MPa. The niobium insert produced brittle niobium/316 L melted zones with UTS of 160 ± 10 MPa, because of the formation of Fe2Nb and Fe7Nb6 layers at the niobium/316 L interface. The addition of a copper insert between niobium and steel allowed avoiding the development of Fe-Nb brittle intermetallics thanks to the absence of brittle phases in Cu-Nb system. For optimal welding conditions, a ductile fracture occurred in the copper interlayer at maximal UTS of 255 ± 10 MPa

Microstructural and micro-electrochemical study of a tantalum-titanium weld interface

International audienceLaser welding offers an array of advantages compared to conventional fusion welding techniques, such as a higher welding speed and lower thermal distortion. However, information about the key aspects of the welding of dissimilar materials remains limited. Therefore, we chose to study the weld interface between tantalum and Ti-6Al-4V, which have good metallurgical compatibility but highly different thermophysical properties that can lead to pronounced chemical heterogeneities. An SEM analysis of the microstructure clearly revealed the formation of an unmixed zone in the melted area and a DRX analysis highlighted the presence of a beta(Ta,Ti) solid solution, tantalum islets and possibly alpha'-titanium where betagenic tantalum was absent. In terms of electrochemical behaviour, the titanium content was the main indicator of oxidation phenomena: a content greater than 50% resulted in a stable passive film, while lower Values led to an oxidation peak at approximately 1.7V vs Ag/AgCl. These results suggest that a reliable laser welding process.must promote a high titanium content in the melted area. This may be achieved through am optimized process with a heat source that shifts away from the tantalum in order to minimize tantalum levels in the melted area