Papers by Author: Thierry Baudin

Abstract: An investigation has been done to study the effect of heat treatment at low temperature on the development of mechanical and electrical properties of the industrially cold drawn aluminum alloy wires (6101). This aluminum alloy is used by the national company of electric cables of Biskra (ENICAB) for the transmission lines of electrical energy. The mechanical and electrical properties of the Al-Mg-Si alloys can be changed by heat treatment. Different technical procedures have been used In order to understand the complicated effect of aging on 6101 aluminum alloy; we have used the optical microscopy, hardness measurements and the electrical resistivity measurement. It was noted that the cold drawing of this aluminum alloy increase the microhardness which is produced by a high strain hardening of the material accompanied by a development of a fibrous texture. We notice also that the electrical resistivity of the alloy increase with an increase of the deformation level and decrease of this properties with the increasing aging time at 170 ° C.

Abstract: The influence of High-Pressure Torsion (HPT) on texture and superplasticity in an Al-7075 was studied using X-ray diffraction and tensile testing. The alloy was processed by HPT at room temperature under a pressure of 6.0 GPA up to a maximum of 20 turns. The pole figures were measured at mid-radius of the disks after 1, 5, 10 and 20 turns. The results show the presence of a typical torsion texture during HPT, in particular, the C{001}<110> component was found to develop preferentially. With increasing deformation, the A {111}<110> and the C components are reinforced after 5 turns and the texture tends to be random with the presence of a fibre texture near the center. Moreover, the fraction of C components tends to gradually decrease and a fairly isotropic microtexture is apparent after 20 turns. Tensile testing showed the development of excellent superplastic properties in this alloy with elongations up to ~700% when testing at a temperature of 623 K.

Abstract: In this study, a monotonous mechanical test is performed on a sample in Al-alloy containing about twenty-five grains. During this test, both the total and elastic intragranular strain fields are measured at the same time. The former field is observed by digital image correlation technique while the latter one is measured by X-ray diffraction. The strain fields obtained are then dedicated to identify the parameters of a crystalline constitutive model, using finite element simulation.

Abstract: In this investigation, grain orientation has been studied in an industrial aluminium Al99.5 which has been welded by TIG process. The optical microscopy and EBSD (Electron Back Scattered Diffraction) were the main techniques used to illustrate the effect of welding on grain orientation in fusion zone and in heat affected zone. Epitaxial growth has been observed in weld joint and texture of each zone has been determined. On the other hand, the effect of isothermal heat treatment at 400 °C on homogenization of welded joint has been also studied. It was shown that the cube orientation {001}<100> is the dominant texture component in welded joint before or after heat treatments.

Abstract: The change in crystallographic orientation distribution during deformation by deep drawing in mild steel has been investigated in order to understand their role in initiation and propagation of crack. The results show that the change of grain orientation from the initial recrystallization texture component of {111}<112> to deformation orientation {111}<110> incites the initiation and propagation of transgranular cracking in the region of {111}<112> small grains. Moreover, the transgranular misorientation and local orientation are analyzed in detail to discuss the change from {111}<112> to {111}<110>. The SEM-EBSD technique was used to reveal that change of orientationm, XRD was performed for the characterization of the global evolution of texture for deformed samples.

Abstract: The evolution of the recrystallization microstructure at different temperatures and the related change in the microhardness were studied in an Al-6061 alloy after 2 turns of high-pressure torsion (HPT) by means of Vickers microhardness and EBSD analysis. The corresponding results show that HPT processing introduces a significant grain size refinement for the deformed state by comparison with the 150 µm grain size in the initial material. The microstructure after annealing at 200°C is relatively close to the as-processed one and the distribution of misorientation angles remains essentially unchanged. However, significant microstructural changes are produced with increasing annealing temperature and at the highest temperature (400°C) there is an abnormal grain growth. The variation of Vickers microhardness (Hv) after the different annealing treatments show a gradual decrease when the temperature increases.

Abstract: The objective of this study was to determine the effect of ECAP-processing on the texture and the microstructure development of the deformed and recrystallized material. The commercial purity AA4343 aluminium alloy, containing very large second phase particles (SPP) of pure silicon, was deformed via route C up to 10 passes and then annealed. The samples were characterized by TEM and SEM equipped with high resolution EBSD. It was found that the microstructure of the deformed state in areas far from coarse SPP was very similar to that observed in pure aluminium. The orientations of the new grains were scattered but not random and only specific groups of orientations were observed.

Abstract: The objective of this study was to determine the effect of deformation mode on recrystallization behavior of severely deformed material. Commercial purity AA3104 aluminum alloy was deformed via high pressure torsion and equal channel angular pressing to different strains and then annealed to obtain the state of partial recrystallization. The microstructure and the crystallographic texture were analysed using scanning and transmission electron microscopes equipped with orientation measurement facilities. The nucleation of new grains was observed in bulk recrystallized samples and during in-situ recrystallization in the transmission microscope. Irrespective of the applied deformation mode, a large non-deformable second phase particles strongly influenced strengthening of the matrix through deformation zones around them. It is known that relatively high stored energy stimulates the nucleation of new grains during the recrystalization. In most of the observed cases, the growth of recrystallized grains occurred by the coalescence of neighboring subcells. This process usually led to nearly homogeneous equiaxed grains of similar size. The diameter of grains in the vicinity of large second phase particles was only occasionally significantly larger than the average grain size. Large grains were most often observed in places far from the particles. TEM orientation mapping from highly deformed zones around particles showed that orientations of new grains were not random and only strictly defined groups of orientations were observed.

Abstract: Dynamic recrystallization mechanisms have been studied after 5182 aluminum Friction Stir Spot Welding (FSSW) and dissimilar friction stir spot welding of 6016 aluminum alloy to IF-steel using EBSD measurements. Moreover, welds have been ice quenched after welding to state on the post-dynamic microstructure evolution after the tool removal. For the Al/Al welds, fine recrystallized grains of the stir zone result from a continuous dynamically recrystallization mechanism followed by a post-dynamic recovery that reduces the low angle boundary fraction in the periphery of the pin. As far as the dissimilar Al/Fe welds are concerned, steel grains of the base metal were fragmented into sub-grains in the thermomechanically affected zone. Nevertheless, recrystallized grains of the stirred zone were about three times larger than these sub-grains. In this case, the continuously recrystallized grains undergo a post-dynamic grain-growth during friction stir welding cooling. In the upper aluminum sheet, the recrystallization mechanisms are the same as in the Al/Al welds.

Abstract: The objective of this study was to determine the effect of ECAP-processing on the texture and the microstructure development of the deformed and recrystallized states. The commercial purity AA3104 aluminum alloy was deformed via route A up to 7 passes and then annealed to obtain the state of partial recrystallization. The shear bands formation and the texture transformation in annealing were investigated with the use of high resolution transmission and scanning electron microscopes equipped with the facilitates for the local orientation measurements. It was found that the instability of the layered structure of the flat grains within some narrow areas led to the formation of the kink-type bands, which were precursors of the shear bands. The orientations of the new grains occurring in the recrystallized samples were not random, i.e. only specific groups of orientations were observed. In most of the observed cases, the growth of the recrystallized grains led to nearly homogeneous equiaxed grains of a similar size.