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

Toxicological Assessment of an Acrylic Removable Orthodontic Appliance Using 2D and 3D In Vitro Methods

Malocclusion is a global health problem, mainly affecting children and adolescents. For this reason, orthodontic treatment must be, on the one hand, safe, non-toxic, and effective and, on the other hand, it must have the best possible esthetic profile. Thus, the use of orthodontic appliances is addressed to all age groups, including young children, for a long period of time, which is why their safety profile is a matter of real interest. For this reason, the purpose of the present study was to evaluate the safety and biocompatibility of an acrylic removable orthodontic appliance made of polymethylmethacrylate and stainless steel alloy made by our team of researchers. To verify the biocompatibility of the medical device, it was immersed in artificial saliva with three different pHs (3, 7, and 10) for a period of ten days. Subsequently, the three types of saliva were tested on human keratinocytes (HaCaT cell line) in terms of viability and modification of cell morphology. Finally, the use of 3D reconstructed human epidermis verified the cytotoxic and irritating potential of the medical device, thus providing relevant information regarding its biocompatibility. The results revealed that by maintaining the orthodontic device in the saliva there is no release of substances with a toxic effect on the human keratinocytes and on the 3D reconstructed human epidermis. There were also no significant changes in cell morphology. In conclusion, it is suggested that the acrylic removable appliance has a safety profile recommended for in vivo use