is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. AbstractThe 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.

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is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. a b s t r a c tFriction stir welding induces a microstructural evolution and residual stresses that will influence the resulting mechanical properties. Friction stir welds produced from magnesium alloy hot rolled plates were studied. Electron back scattered diffraction was used to determine the texture evolution, residual stresses were analysed using X ray diffraction and tensile tests coupled with speckle interferometry were performed. The residual stresses induced during friction stir welding present a major influence on the final mechanical properties.

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is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. a b s t r a c tA laser surface melting treatment (LSMT) was performed on a ZE41 Mg-alloy using an excimer KrF laser. The laser-melted layer depth depends on the laser scan speed. The morphology and the microstructure of the laser-melted surface were characterized, thanks to the scanning electron microscopy (SEM). The melted Mg-alloy presented a homogenous distribution of the alloying elements in the magnesium matrix. The laser surface melting treatment increased the microhardness of the ZE41 Mg-alloy and improved its corrosion resistance.

Magnesium alloys have interesting specific characteristics [1] including the best strength/weight ratio of all commercial alloys. Their high thermal conductivity facilitates heat transfer. A high damping capacity means good impact resistance and noise reduction. They are also recyclable. The need to reduce the fuel consumption of vehicles or planes, and thus the weight, encourages manufacturers to use magnesium alloys because of their low density and important properties.In the automotive industry magnesium alloys are used for welded structures in different vehicle parts like seat frames and dashboard parts (Fig. 1). In aerospace, magnesium alloys are used for gearbox casings, oil sumps, helicopter turbines, aircraft wheels, seat structures etc.The machining of magnesium alloys requires processes with high energy density and shielding gases that effectively protect the metal from the action of oxygen. Therefore, we favor the laser beam as a machining tool for this material. There has been little research into laser welding of magnesium alloys, and this field is still under development. [2,3] In this communication, we present experimental results for CO 2 laser welding of AZ91 (2 mm thickness) for the automotive industry and WE43 (4 mm thickness) for the aerospace industry.The process parameters were varied in the following ranges: laser power, 1±5 kW; welding speed, 1±7 m/min; focal position, ±3 mm to +3 mm relative to the metal surface; shielding gas for welding, helium or argon with a flow of 10±60 L/min at 4 bar. Laser power, welding speed, focal position, and shielding gas flow are considered as the base laser welding parameters and have been optimized for high welding quality. Metallurgical analysis and mechanical testing were performed (macroscopic structure, microscopic structure, phase analysis, chemical composition, hardness, tensile strength etc.) to understand the influence of the welding parameters. For a given laser power, we find that the welding speed and the focal position strongly influence the macroscopic and microscopic characteristics, whereas the effect of the shielding gas flow is weak. Microscopic examinations show that the grain size is clearly reduced without formation of porosity, neither cracks nor inclusions. Indeed, the measured Vickers microhardness of the weld bead is slightly higher than that of the bulk metal. Experiments allowed us to obtain adequate parameters for high welding quality without using filler material. A numerical simulation is in progress to calculate the temperature field in the keyhole and the shape of the weld.Experiments were carried out using a 5 kW CO 2 laser having the following properties: mode, TEM 01 ; divergence, < 1.5 mrad; beam diameter on focusing optic, 38 mm; focused diameter is 0.25 mm. A parabolic mirror with a focal length of 150 mm was used for focusing the beam. Alloys AZ91 and WE43 were used in the form of plates of different thicknesses. Helium was selected as the shielding gas during these welding tests (for its properties of great thermal c...

is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. b s t r a c tIn this paper, a three-dimensional finite element model is developed to simulate thermal history magnesium-based alloys during laser beam welding. Space-time temperature distributions in weldments are predicted from the beginning of welding to the final cooling. The finite element calculations were performed using Cast3M code with which the heat equation is solved considering a non-linear transient behaviour. The applied loading is a moving heat source that depends on process parameters such as power density, laser beam dimensions and welding speed, and it is associated to moving boundary conditions. Experiments were carried out to determine temperature evolution during welding and to measure the laser weld width. By comparing the thermal model answers with the measurements, it is found that numerical simulations results are in a good agreement with the experimental data.

Metallic alloys with a low mass density can be considered to be basic materials in aeronautic and automotive industry. Magnesium alloys have better properties than aluminium alloys in respect of their low density and high resistance to traction. The main problems of magnesium alloy welding are the inflammability, the crack formation and the appearance of porosity during the solidification. The laser tool is efficient to overcome the difficulties of manufacturing by conventional processing. Besides, the laser processing mainly using shielding gases allows an effective protection of the metal against the action of oxygen and a small heat affected zone.