Generation and characterization of T40/A5754 interfaces with lasersPatrice

Laser-induced reactive wetting and brazing of T40 titanium with A5754 aluminum alloy with 1.5 mm thickness was carried out in lap-joint configuration, with or without the use of Al5Si filler wire. A 2.4 mm diameter laser spot was positioned on the aluminum side to provoke spreading and wetting of the lower titanium sheet, with relatively low scanning speeds (0.1–0.6 m/min). Process conditions did not play a very significant role on mechanical strengths, which were shown to reach 250–300 N/mm on a large range of laser power and scanning speeds. In all cases considered, the fracture during tensile testing occurred next to the TiAl3 interface, but in the aluminum fusion zone. The interfacial resistance was then evaluated with the LASAT bond strength tester, based upon the generation and propagation of laser-induced shock waves. A 0.68 GPa uniaxial bond strength was estimated for the T40/A5754 interface under dynamic loading conditions

Modélisation numérique avec apport de matière du soudo-brasage des assemblages hétérogènes acier / aluminium

Dans cette étude nous abordons la modélisation numérique thermomécanique du soudo-brasage de tôles d'acier et d'aluminium par la technique CMT dans une configuration à clin. Ces métaux ont des coefficients de dilatation thermique différents, ce qui provoque des déformations et des contraintes résiduelles élevées. Cette simulation prend en compte l'apport de matière durant le processus. Une validation de la modélisation est faite sur le cas simple du dépôt d'un cordon de matériau d'apport sur une plaque d'aluminium. Pour l'assemblage hétérogène des comparaisons sont faites entre les résultats numériques et expérimentaux en termes de déplacements hors-plan

Maîtrise des interfaces hétérogènes lors d'une opération de soudo-brasage (application au couple aluminium - magnésium)

Les travaux concernent l'étude de l assemblage dissimilaire d alliages d'aluminium (Al4043, Al5356) et de magnésium (RZ5, AZ31) par les procédés CMT et laser. La méthode des plans d'expériences statistiques a été mise en oeuvre afin d'analyser les effets des paramètres opératoires de soudage et la nature chimique des substrats et des fils d apport. Les effets chimiques, thermomécaniques et énergétiques ont été étudiés dans l'objectif de contrôler et de diminuer l épaisseur de la couche intermétallique formée entre la zone fondue et le métal de base et considérée comme critique pour la fissuration. La microstructure a été caractérisée par microscopie optique, MEB, EDS, rayons X, dureté et nano-indentation.La rupture dans la couche d interface est liée à la formation de composés intermétalliques (Al3Mg2, Al12Mg17), d'une dureté jusqu à 350 HV0,025, ainsi qu'à l'épaisseur de la couche et des éléments d'alliage. Le RZ5 a été assemblé avec succès avec le fil d apport Al4043 par les deux procédés CMT et laser.Suite à l analyse systématique des résultats, qui montre un meilleur comportement d Al4043/RZ5 qui contient du zirconium, l'ajout de cet élément dans la zone fondue a permis de montrer une amélioration de la qualité des joints par effet sur la microstructure.Pour l assemblage laser, une modification des conditions des vitesses de refroidissement par un pompage thermique plus rapide par l utilisation d un support de plaques de cuivre a induit une modification des couches d'interface et montre tout l'intérêt de maîtriser les conditions opératoires. Par ailleurs, une vibration ultrasonore des substrats a été testée pour modifier la formation des zones problématiquesThis work concern a study of the dissimilar joining of aluminium (Al4043, Al5356) and magnesium (RZ5, AZ31) by CMT and laser welding process. The method of statistical design of experiments has been implemented in order to analyse the effects of the technological welding parameters and the chemical nature of the base and filler metal. The chemical, thermo-mechanical and energetic effect were studied with the aim to control and decrease the thickness of the intermetallic layer formed between the melted zone and the base metal and considered to be critical to cracking. The microstructure was studied by optical and SEM microscopy, EDS, X-ray, hardness and nanoindentation.The fracture produced in the interface layer has been related to the intermetallic compounds (Al3Mg2 and Al12Mg17), with a hardness up to 350 HV0.025, as well of the thickness of the interface layer and to the alloying composition. The RZ5 as base metal was successfully joined with the Al4043 welding wire, in both CMT and laser process.According to the systematically analyse, who shows a better welding ability of the couples Al4043/RZ5, which contains zirconium, by the adding of this element in the molten metal the welding ability improvement was showed.For the laser joining, a modification of the cooling condition by a accelerate thermal cycle, by using a copper support for the base metal was induce a modification of the interface layer, showing the interest of mastering the technical condition. Moreover, a ultrasonically vibration of the base metal was tested in attempting to modify the formation of the problematical zonesDIJON-BU Doc.électronique (212319901) / SudocSudocFranceF

Aluminum to titanium laser welding-brazing in V-shaped grooveI

Laser assisted joining of AA5754 aluminum alloy to T40 titanium with use of Al-Si filler wires was carried out. Continuous Yb:YAG laser beam was shaped into double spot tandem and defocalized to cover larger interaction zone in V shaped groove. Experimental design method was applied to study the influence of operational parameters on the tensile properties of the joints. Microstructure examination and fractography study were carried out to understand the relation between local phase content and fracture mode. Within defined window of operational parameters, statistically important factors that influenced the strength of T40 to AA5754 joints in V groove configuration were Si content in the filler metal and groove opening angle on T40 side. The best quality joint showed joint coefficient of 90% (or 200 MPa of apparent UTS). Tensile strength of the joints was found to be determined by the proportion between well-developed and under-developed reaction zones of T40/melted zone interface. The formation of 2–25 μm thick Si-rich interlayers composed by Ti5Si3 and τ2 proved to enhance the strength of brazed interface. The creation of very thin (<0.5 μm) Si-rich layers at the bottom of the groove was found not sufficient to establish mechanical continuity of the joint and thus should be avoided

Direct keyhole laser welding of aluminum alloy AA5754 to titanium alloy Ti6Al4V

The tensile strength of direct AA5754/Ti6Al4V joints performed by high speed Yb:YAG laser welding is found to be determined by morphology and phase content of dissimilar interface formed between contacting Al-rich and Ti-rich melted zones. Three types of contact interfaces were observed: (1) thin (10 m/min. Maximal linear tensile force (220 N/mm for 2 mm thick weld) can be attained when thin contact interface is formed. In this case, the fracture starts in intermetallics-rich zone but propagates mainly in Al-rich melted zone, when in other cases it occurs in brittle intermetallic layers

Study of magnesium and aluminum alloys absorption coefficient during Nd:YAG laser interaction

International audienceIn laser processes, the absorption factor of laser Nd:YAG by metals plays a very important role. In order to model laser welding, we need to know its evolution during the process. The theoretical calculation does not enable the prediction of the absorption factor in the case of a keyhole mode. It is difficult to predict the effect of plasma and recoil pressure on the shape of the keyhole. In this paper, an integrating sphere is used to determine the absorption factor during the laser process, which is carried out on two types of magnesium alloys (WE43 and RZ5) and an aluminum alloy. We obtain the evolution in time of the absorption factor according to different steps of the evolution of the keyhole

Improvement in friction by cw Nd:YAG laser surface treatment on cast iron cylinder bore

International audienceThe reduction of the oil-film thickness in the piston-assembly of automobile engines has lead to it now being necessary to add a cylinder–bore surface treatment, so that oil reserves can be created on it. However in doing this, the initial plateaued texture must be kept. With a Nd:YAG laser source treatments oil reserves holes are formed, which respect the function of the initial bore surface texture. The material, cast iron, is heterogeneous: perlitic matrix and carbon lamellae. The laser treatment will make use of this heterogeneity: as under a cw laser beam, using graphite, with its good insulating material properties, carbon lamellae, which are near the surface, are revealed. Also a high density of lamellae in a hollow against the surface are obtained. In order to improve these new surfaces, friction tests were conducted on a friction bench using samples from engine components as test pieces. In order to know bore roughness evolution, 3D surface topography measurements were made before and after as well as friction tests on surfaces without laser treatment and with laser treatment. The results indicate that these holes can improve oil lubrication time

Assemblage hétérogène cuivre-inox et TA6V-inox par les faisceaux de haute énergie (compréhension et modélisation des phénomènes physico-chimiques)

La présente étude est dédiée à la compréhension des mécanismes de malaxage intervenant lors du soudage de matériaux dissimilaires par des sources de haute énergie et en particulier sur deux couples de matériaux présentant des problèmes métallurgiques différents : cuivre - inox (lacune de miscibilité, différence de propriétés thermophysiques), TA6V- inox (oxydation, formation de phases intermétalliques fragilisant la soudure).Pour le premier couple de matériaux, le soudage par laser Nd:YAG continu et par faisceau d'électrons a été utilisé. L'étude des évolutions de la morphologie des soudures, de la composition et de la microstructure des zones fondues ainsi que des propriétés mécaniques a permis de proposer des hypothèses sur les mécanismes de formation du mélange hétérogène à solubilité limitée. Afin de quantifier les phénomènes physiques intervenant en soudage continu de matériaux dissimilaires, la modélisation numérique a été mise en œuvre en utilisant le logiciel FEM "Comsol Multiphysics". Une série des modèles simulant les champs de températures, les mouvements convectifs et le malaxage (diffusion, méthode level set, méthode des champs de phases) a été créée. Dans le cas du laser, la formulation pseudo-stationnaire du transfert de chaleur basée sur la géométrie du capillaire simplifiée et la convection a été couplée avec les problèmes 2D de diffusion et de malaxage des matériaux dans différents plans horizontaux. En soudage par faisceau d'électrons, la morphologie de la microstructure a nécessité une formulation temporelle. Le modèle multiphysique final en couplage complet (solution multiphysique simultanée) reproduit le processus de formation d'une structure périodique de solidification lors du soudage par faisceau d'électrons et permet d'expliquer l'aspect des structures alternées entre matériaux immiscibles ou présentant de grandes différences de propriétés thermophysiques.Le deuxième couple de matériaux présente des problèmes métallurgiques majeurs liés à la formation des phases intermétalliques rendant l'assemblage direct par fusion impossible. La composition locale devient donc l'aspect-clef de la formation d une soudure correcte : l'introduction d un troisième matériau (cuivre) ayant une meilleure compatibilité avec le titane est nécessaire. Pour pouvoir déterminer les fenêtres optimales des conditions opératoires, les modèles numériques, créés précédemment, ont été adaptés pour quatre procédés de l assemblage : faisceau d'électrons, soudage lasers Nd:YAG continu et pulsé, brasage par laser avec apport de fil. L'analyse élémentaire des microstructures dans les soudures résistantes mécaniquement a permis de développer le scénario de la solidification d'une zone fondue et de comprendre l'influence de la composition aux interfaces sur la résistance mécanique des assemblages.Les modèles numériques multiphysiques créés au cours de cette étude permettent l'accès rapide à la grande quantité d'information sur le comportement de la zone fondue en fonction des paramètres de soudage en se basant sur le nombre des données de départ relativement limité et sur quelques hypothèses simplificatrices. L'approche multiphysique à la modélisation de soudage permet de reproduire la forme de la zone fondue, visualiser les écoulements du liquide et cartographier la distribution de certains éléments avec une bonne corrélation avec les résultats expérimentaux. L'ensemble des modèles permet de déterminer les conditions opératoires répondant aux critères fixes en fonction de la métallurgie d'un couple hétérogène.The present study is dedicated to the comprehension of the mechanism of materials mixing during dissimilar welding by high power beam sources. We have been interested in joining of two couples of metallic materials which present different metallurgical problems: copper- stainless steel (miscibility gap, important difference in physical properties); TA6V- stainless steel (oxidation on air, formation of intermetallic phases which made the joint brittle).For the first couple of materials, continuous laser Nd:YAG welding and electron beam welding have been applied. The experimental study of morphology evolution, composition, microstructure and mechanical properties has allowed establishing the hypotheses on formation of heterogeneous mixture between the materials having limited solubility. To quantify the physical phenomena of continuous dissimilar welding, the numerical modeling has been carried out by means of FEM software package "Comsol Multiphysics". A number of models reproducing temperature field, convection movements and mixing (diffusion, level set method, phase field method) between the materials has been created. In case of continuous laser welding, the pseudo-stationary formulation of heat transfer based on simplified key-hole geometry and convection has been coupled with two-dimensional problems of diffusion and mixing in horizontal planes. The electron beam welding presenting the nonlinear development of the weld has needed employing of temporary formulation. Final model including complete coupling (simultaneous multiphysical solving) reproduces the process of development of periodic solidification structure during electron beam welding and allows explaining the mechanism of formation of altered structures between immiscible materials which have important difference in thermophysical properties.The second couple of materials presents weldability problems due to formation of brittle intermetallic phases making direct joining by fusion impossible. The local elementary composition becomes the key-aspect of successful joining: the introduction of the third material (pure copper) having better compatibility with titanium is necessary. To determine the ranges of optimal operational conditions, numerical models created previously have been adapted to the case of four joining techniques: electron beam and laser Nd:YAG (continuous and pulsed) welding and laser brazing with filler wire. Elementary analysis of microstructures of resistant welds has allowed developing the solidification scenario and understanding the influence of local composition of heterogeneous interfaces on tensile properties of the joints. The multiphysical models created during this study allow rapid access to high quantity of data on behavior of melted zone in function of welding parameters basing on relatively limited input data and several simplification hypotheses. The multiphysical approach to welding modeling allows recreating the shape of melted zone, to visualization the convection movements and providing the cartography of several elements in good correspondence with experimental results. A set of models allows determination of operational parameters respecting fixed criterions determined by metallurgy of dissimilar couple.DIJON-BU Doc.électronique (212319901) / SudocSudocFranceF

Magnesium alloys laser (Nd:YAG) cladding and alloying with side injection of aluminium powder

International audienceThe development of the high purity magnesium alloys (such as WE43) incites the designers to reconsider them, and the car industry appears, these days, the most interested to use this kind of alloy. However, due to their ignitability and tendency to oxidation, magnesium alloys require surface treatments. A series of experiments was carried out in order to improve the corrosion resistance of two types of magnesium alloys, WE43 and ZE41. In most cases, the substrate surface was treated before laser interaction. Side injection of aluminium powder under a 3 kW cw Nd:YAG laser was employed. The deposited layers present very good bond properties. The resulting microstructure was analysed and some mechanical properties determined, such as hardness, which is increased due to the Al3Mg2 and Al12Mg17 intermetallic formation. The results obtained represent an important step to achieve an enhanced corrosion resistance for magnesium alloy

Gas protection optimization during Nd:YAG laser welding

International audienceMany laser processes, such as welding or surface treatments are associated with an undesired phenomenon, which is oxidation. The solution commonly employed to solve this problem approaches the shielding gas and/or the shielding gas device. What we propose in this paper is a methodology with the goal to optimize the protection gas device design as well as the gas flow in the case of laser welding and surface treatments. The pressure created by the gas flow on the sample surface is recorded and analysed together with the operating parameters influence in order to reach the objectives. The nozzle system designed and presented below assures the protection against material oxidation using minimal gas flow rates and increases the welding penetration in the case of high-power Nd:YAG laser welding