Friction stir welding of AZ31 magnesium alloy rolled sheets: Influence of processing parameters

The temperature evolution during friction stir welding (FSW) and the resulting residual stresses of AZ31 Mg alloy were studied to get a better understanding of the mechanisms involved in this process. The relationship between the processing parameters, the heat and plastic deformation produced and the resulting microstructure and mechanical properties was investigated. Increasing the shoulder diameter or the tool rotation speed or decreasing the welding speed produced an increase in the heat generated during the process and then promoted grain growth. The temperature distribution on the advancing side and on the retreating side differed, and stress levels were higher on the retreating side. The grain size heterogeneity produced by FSW was not the prevailing cause of failure.AEROMAG Project N°AST4-CT-2005-516152 European Unio

Texture evolution in Nd:YAG-laser welds of AZ31 magnesium alloy hot rolled sheets and its influence on mechanical properties

AZ31 hot rolled magnesium alloy presents a strong basal texture. Using laser beam welding (LBW) as a joining process induces high temperature gradients leading to major texture changes. EBSD was used to study the texture evolution, and tensile tests coupled with speckle interferometry were performed to understand its influence on mechanical properties. The random texture obtained in the LBW fusion zone is mainly responsible for the yield strength reduction.AEROMAG Project N°AST4-CT-2005-516152 European Unio

Effects of Ag or Si on precipitation in the alloy Al-2.5% Cu-1.5% Mg

International audienceCalorimetric measurements and electron microscopy observations were performed on Al-2.5 mass% Cu-1.5 mass% Mg alloys containing also 0.4, 1 or 2 % Ag or 0.5 % Si, in order to improve understanding of the relationships between precipitation processes and age hardening. The analogous behaviour of calorimetric and hardness data confirms that the first hardening stage is initiated in all alloys by GPB zone formation which occurs via a nucleation and growth controlled mechanism. The vacancy-trapping effect of Mg is increased by Ag and Si additions and leads to slower precipitation kinetics. Consequently refined GPB zones sizes are obtained leading to an increase in hardness with respect to the ternary alloy. During the second hardening stage, the formation of the more stable S' phase increases the total amount of strengthening precipitates in the ternary alloy. Phases typical for binary Al-Cu alloys form additionally in the Si-containing alloy. In the Ag-bearing alloys, precipitation of the hardening X' phase occurs the earlier the higher the Ag content is; it is followed by S' precipitation. During heating of the ternary alloy, the S'phase forms after substantial dissolution of GPB zones and of the S" phase identified by high resolution electron microscopy; this contradicts the concept of a continuous precipitation sequence

Garantir un réel accès à la justice efficace aux travailleuses domestiques migrantes : obstacles systémiques et conceptualisation du droit - perspectives canadiennes et internationales

Malgré une demande croissante dans le secteur du travail domestique et un poids économique mondial considérable, les travailleuses domestiques migrantes demeurent parmi les plus précaires et les plus exploitées de la planète. Invisibles, isolées et travaillant pour des particuliers dans des résidences privées, elles échappent aux catégories traditionnelles d’emploi. Ces travailleuses se retrouvent alors à évoluer en marge du cadre légal ou encore, elles peinent à faire appliquer correctement les lois conçues pour les protéger. Ce mémoire cherche donc à analyser les manières d’envisager le droit afin de garantir un réel accès à la justice pour les travailleuses domestiques migrantes. En abordant d’abord les obstacles systémiques qui font échec à la réglementation du secteur domestique à travers le monde, cette recherche démontre une inadéquation du droit traditionnel à la réalité des travailleuses par l’analyse des effets de la réglementation canadienne qui leur est applicable. À la lumière de la récente Convention concernant le travail décent pour les travailleuses et travailleurs domestiques, ce mémoire démontre qu’une conceptualisation du droit basée sur le pluralisme juridique fournit des alternatives aux travailleuses domestiques migrantes pour accéder à la justice. Ultimement, l’empowerment de ces travailleuses par leur inclusion dans le dialogue social couplé à une réglementation adaptée à leur réalité permettra d’assurer une protection efficace de leurs droits.In spite of an ever increasing demand in the domestic work sector and a considerable worldwide economic weight, migrant domestic workers are among the most precarious and exploited globally. Invisible, isolated and working for individuals in private residences, they fall outside the traditional work categorizations. Therefore, these women find themselves operating in margin of the legal system or, when they are protected by laws, they struggle to have those laws applied efficiently. This research will try to analyze the different ways we can consider law in order to guarantee a real and efficient access to justice to migrant domestic workers. After addressing the systemic obstacles to domestic work regulation worldwide, this research explores the inconsistency between traditional law and the reality of migrant domestic workers by analyzing the effects of the applicable Canadian regulation. In light of the recent Convention concerning decent work for domestic workers, this essay shows that a conceptualization of law based on legal pluralism offers domestic workers an alternative access to justice. Ultimately, including these workers in the social dialogue and implementing specific regulation adapted to their reality will provide them with an empowerment that will insure an effective protection of their rights

Friction stir welding of AZ31 magnesium alloy rolled sheets: Influence of processing parameters

International audienceThe temperature evolution during friction stir welding (FSW) and the resulting residual stresses of AZ31 Mg alloy were studied to get a better understanding of the mechanisms involved in this process. The relationship between the processing parameters, the heat and plastic deformation produced and the resulting microstructure and mechanical properties was investigated. Increasing the shoulder diameter or the tool rotation speed or decreasing the welding speed produced an increase in the heat generated during the process and then promoted grain growth. The temperature distribution on the advancing side and on the retreating side differed, and stress levels were higher on the retreating side. The grain size heterogeneity produced by FSW was not the prevailing cause of failure

Microstructure Characterization of a Nitrided Fe- 3wt.%Cr-0.3wt.%C Model Alloy by Anomalous Small Angle X-ray Scattering

Nitriding is a thermo-chemical surface treatment of steels providing an improved fatigue and wear resistance. This treatment is based on nitrogen diffusion involving the precipitation of nano-scaled nitrides from the solid solution at the near surface of the nitrided piece. Nitriding involves a complex microstructural evolution both in time and depth including diffusion of nitrogen and precipitation of nitrides but also coarsening and dissolution of carbides resulting in diffusion of carbon. However the chemical composition of nano-scaled precipitates remains controversial, in particular regarding the iron content in nano-nitrides that may substitute alloying elements. In this framework, anomalous small-angle X-ray scattering was used to bring quantitative data on the distribution and composition of the nano-scaled phases in a Fe-3Cr-0.3C steel as a function of depth

Texture evolution in Nd:YAG-laser welds of AZ31 magnesium alloy hot rolled sheets and its influence on mechanical properties

International audienceAZ31 hot rolled magnesium alloy presents a strong basal texture. Using laser beam welding (LBW) as a joining process induces high temperature gradients leading to major texture changes. EBSD was used to study the texture evolution, and tensile tests coupled with speckle interferometry were performed to understand its influence on mechanical properties. The random texture obtained in the LBW fusion zone is mainly responsible for the yield strength reduction

Determination of the volume fraction of precipitates in a nitrided Fe- 0.354 wt% C-2.93 wt% Cr model alloy by anomalous small angle X-ray scattering

Anomalous small angle scattering (ASAXS) is a powerful non-destructive technique that can provide char- acteristic features of nanoscale precipitates such as the volume fraction, and chemical composition. In this paper, the technique is used for the first time to explore nanoscale MN nitrides (M = Cr,Fe) after nitriding of a model iron alloy (Fe-0.354 wt% C-2.93 wt% Cr)

Ferrite recrystallization and austenite formation during annealing of cold-rolled advanced high-strength steels: In situ synchrotron X-ray diffraction and modeling

Ferrite recrystallization and austenite formation occurring during annealing of cold-rolled advanced high-strength steels are key mechanisms as they largely determine the final microstructure and mechanical properties. However, the influence of processing parameters on these mechanisms and their interactions is still not fully understood. This is particularly the case for Dual-Phase steels having an initial cold-rolled microstructure con-sisting of ferrite and martensite before annealing, which were scarcely investigated compared to ferrite-pearlite initial microstructures. In situ synchrotron X-ray diffraction experiments together with post-mortem metallo-graphic analysis allowed clarifying both ferrite recrystallization and austenite formation during annealing of a ferrite-martensite initial microstructure depending on the process parameters of the annealing cycle. Results showed a major influence of recrystallization state on austenite formation, leading to an unexpected effect of heating rate on austenite formation kinetics. A modeling approach was undertaken to rationalize the influence of heating rate on austenite formation by taking into account the bi-phased ferrite-martensite initial microstructure and the effect of ferrite recrystallization state

Potential of multi-species livestock farming to improve the sustainability of livestock farms: A review.

Diversified farming systems are proposed as a major mechanism to address the many sustainability issues of today's agriculture. Multi-species livestock farming, i.e. keeping two or more animal species simultaneously on the same farm, is an option that has received little attention to date. Moreover, most studies of multi-species livestock farming are limited, usually focusing on selected dimensions of farm sustainability and addressing lower organizational levels (i.e. within the farm) and rather limited time horizons (e.g. a few weeks in a grazing season). Thus, a comprehensive assessment of multi-species livestock farming in terms of farm sustainability is lacking. In this context, we outline and discuss potential benefits and limitations of multi-species livestock farming for livestock farm sustainability from existing literature and list issues on multi-species livestock farming requiring further research. We show that multi-species livestock farming has the potential to improve the three dimensions of sustainability reviewed - economic viability for farmers, environmental soundness and social acceptability by being respectful of animals and humans - as long as locally relevant farming practices are implemented, especially an appropriate stocking rate during grazing. If relevant practices are not observed, multi-species livestock farming may produce undesirable effects, such as competition for resource acquisition during grazing, parasitic cross-infection and more intense work peaks. Therefore, we identify four focal research areas for multi-species livestock farming. First, characterizing the management of multi-species livestock farms. To do this, we suggest considering the integration of production enterprises (e.g. cattle and sheep enterprises) within the farm from three perspectives: farming practices (e.g. grazing management), work organization and sales. Second, exploring the complementarity of livestock species on multi-species livestock farms. This is especially true for species combinations that have been largely ignored (e.g. ruminants and monogastrics), even though they may have potential due to complementary diet compositions and resource-acquisition strategies. Third, assessing the sustainability of multi-species livestock farm scenarios (current or alternative) according to the management practices and production conditions, which requires adapting existing methods/models or developing new ones. Fourth, characterizing conditions for success and obstacles for multi-species livestock farming along the value chain from production to consumption, considering stakeholders' objectives, work habits and constraints. Increasing understanding should help prioritize actions and organize them to scale up multi-species livestock farming