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- Influence of Tool Geometry and Process Parameters on Torque, Temperature, and Quality of Friction Stir Welds in Dissimilar Al AlloysPublication . Manuel, Neves; Beltrão, Daniel; Galvão, Ivan; Leal, Rui M.; Costa, José D.; Loureiro, AltinoIn the current investigation, the influence of the tool geometry, the position of the materials in the joint, the welding speed on the temperature and torque developed, and on the quality of the welds in dissimilar and tri-dissimilar T joints were analysed. The aluminium alloys used were AA2017-T4, AA6082-T6, and AA5083-H111 and the friction stir welds were performed with identical shoulder tools, but with either a pin with simple geometry or a pin with progressive geometry. Progressive pin tools proved to be a viable alternative in the production of dissimilar and tri-dissimilar welds, as they provide a larger tool/material friction area and a larger volume of dragged material, which promotes an increase in the heat generated and a good mixing of the materials in the stir zone, although they require a higher torque. Placing a stronger material on the advancing side also results in a higher temperature in the stir zone but requires higher torque too. The combination of these factors showed that tools with a progressive pin provide sound dissimilar and tri-dissimilar welds, unlike single-pin tools. The increase in the welding speed causes the formation of defects in the stir zone, even in tri-dissimilar welds carried out with a tool with a progressive pin, which impairs the fatigue strength of the welds.
- Effect of shoulder cavity and welding parameters on friction stir welding of thin copper sheetsPublication . Leal, R. M.; Sakharova, N.; Vilaça, P.; Rodrigues, D. M.; Loureiro, A.The aim of this investigation was to study the influence of shoulder cavity and welding parameters on torque, defect formation, microstructure and mechanical properties of friction stir welds in very thin sheets of deoxidised copper. Three types of tools were used: a flat shoulder tool and two tools with conical shoulder cavities of 3 and 6° respectively. The welding parameters analysed were tool rotation and traverse speeds. It was observed that the torque, the microstructure and hardness and the formation of defects in the welds are influenced mainly by tool rotation speed and, to a lesser extent, by the traverse speed and shoulder cavity. The tensile properties of welds carried out at high rotation speeds are little affected by the shoulder cavity.
- The Fourth “R” - The Reversion of Objects as a Way of Reducing WastePublication . S. GonçalvesGiven the evident inefficiency of the policies and mechanisms established to deal with environmental degradation, it is essential to understand the reasons for their failures and to try alternative ways to mitigate the environmental problems associated with the replacement of objects. The ideas behind the so-called “3 R’s” policy, born of a sequence of two defining moments in the definition of environmental policies in Europe, - Agenda XXI in 1992 [1] and the 5th European Environment and Development Program of 1993 - have produced encouraging results since their creation, but failed to halt the increasing degradation of the environment on a planetary level. One of the problems derives from the fact that any of r's is strongly dependent on the environmental conscience, or even ethics, of the citizens responsible for the decisions regarding the products in their different moments of existence - from their design and production to their use and subsequent destination. This dependence leads to a high fallibility of environmental policies, insofar as western society suggests, in the way it behaves, a direction opposite to that which they advocate. It is thus important to reflect on ways of designing and producing things whose environmental performance is less dependent on the environmental consciousness of the end user, so that this awareness is not so decisive in the impact resulting from the disposal of objects. The present work tries to analyse the response of a group of students of design to the introduction of a “4thR”, that we call Reversion, and that is to think products of daily use whose form is conditioned by the necessity of its components can be, when dismantled of the system, seen as raw material directly usable for another purpose, easily determined by the user, and not as a technical component of an obsolete system. Functional prototypes will be realized in order to evaluate and validate the products regarding their effective performance in terms of production and use, as well as the possibility of reuse of their components in contexts other than those for which the objects were designed.
- Weldability of aluminium-copper in explosive weldingPublication . Carvalho, G. H. S. F. L.; Galvão, I.; Mendes, R.; Loureiro, A.; Leal, RuiA large number of aluminium-copper explosive welds were produced under different welding conditions to perform a broad analysis of the weldability of this combination. The influence of the explosive mixture and the relative positioning of the plates on the welding results were analysed. When the aluminium alloy is positioned as the flyer plate, continuous interfacial melting occurred under the low values of energy lost by the collision, and collision point velocity. This proved that the weldability of the aluminium-copper combination is higher when the copper is positioned as the flyer. A mismatch between the experimental results and the existing theories that define the requirements for achieving consistent welds was noticed. Especially for welds produced using the aluminium alloy as the flyer, the experiments proved to be more restrictive than the theories. These theories, despite being widely applied in dissimilar welding literature, present several limitations concerning aluminium-copper welding. New approaches considering the formation of intermetallic phases at the interface, the properties of both welded metals, and/or the difference in their properties should be developed
- Effect of explosive ratio on explosive welding quality of copper to aluminiumPublication . Loureiro, A.; Mendes, R.; Ribeiro, J. B.; Leal, R. M.The goal of this research is to study the influence of the ratio of an explosive composed of 80% ANFO and 20% matrix on the quality of dissimilar explosive welds of Cu-DHP copper to aluminium alloy 5083-H11, in flat configuration. It is analysed the influence of four explosive ratios (1.4, 1.8, 2.3 and 2.6) on the microstructure and mechanical properties of welds. It was observed that the increase in the explosive ratio gives rise to an increase of the collision point velocity (Vc) and the impact velocity (Vp) and consequently reduces the thickness of the flying plate after welding as well as produces wavy interfaces of greater amplitude. Microstructural analysis showed the formation of hard and brittle intermetallic compounds in the interface region, more obvious in welds made with higher ratio of explosive.
- Influence of base material properties on copper and aluminium–copper explosive weldsPublication . Carvalho, G. H. S. F. L.; Galvão, I.; Mendes, R.; Leal, Rui; Loureiro, A.The influence of base material properties on the interfacial phenomena in copper and aluminium–copper explosive welds was studied. Two explosive mixtures with different detonation velocities were tested. Sound aluminium–copper joints with effective bonding were achieved by using an explosive mixture with a lower detonation velocity. High energy explosives led to extensive interfacial melting, preventing the production of consistent dissimilar welds. Unlike to the similar copper joints, the aluminium–copper welds presented very asymmetrical interfacial waves, rich in intermetallic phases and displaying a curled morphology. The interaction of the materials in dissimilar welding was found to be completely different depending on the positioning of each alloy in the joint, i.e. positioned as the flyer or as the baseplate.
- Aluminum-to-Steel Cladding by Explosive WeldingPublication . Carvalho, Gustavo H. S. F. L.; Galvão, Ivan; Mendes, Ricardo; Leal, Rui M.; Loureiro, AltinoThe production of aluminum-carbon steel and aluminum-stainless steel clads is challenging, and explosive welding is one of the most suitable processes to achieve them. The present work aims to investigate the coupled effect of two strategies for optimizing the production of these clads by explosive welding: the use of a low-density interlayer and the use of a low-density and low-detonation velocity explosive mixture. A broad range of techniques was used to characterize the microstructural and the mechanical properties of the welds, specifically, optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, electron backscatter diffraction, microhardness and tensile-shear testing with digital image correlation analysis. Although aluminum-carbon steel and aluminum-stainless steel have different weldabilities, clads with sound microstructure and good mechanical behavior were achieved for both combinations. These results were associated with the low values of collision point and impact velocities provided by the tested explosive mixture, which made the weldability difference between these combinations less significant. The successful testing of this explosive mixture indicates that it is suitable to be used for welding very thin flyers and/or dissimilar materials that easily form intermetallic phases.
- Explosive welding of aluminium to stainless steel using carbon steel and niobium interlayersPublication . Carvalho, G.H.S.F.L.; Galvão, I.; Mendes, R.; Leal, R. M.; Loureiro, A.This work aimed to study aluminium to stainless steel explosive welds produced using two different interlayers: carbon steel and niobium. The use of each interlayer was analysed and compared microstructurally and mechanically using many characterisation techniques. The final joints using both interlayers presented favourable interfacial microstructure: waves on both interfaces. However, the joint using the carbon steel interlayer showed the best mechanical properties compared to the joints using the niobium interlayer. All interfaces found on both welds were wavy. However, depending on the metallic alloy combination, the shape of the wave is completely different. The results suggest that the shape of the waves is influenced by the shock impedance mismatch of the materials being welded. The impedance mismatch parameter (IMP) developed for explosive welding in this work proved to be a compelling method to order metallic combinations in a single axis to estimate the tendency to form typical or curled waves. Typical symmetrical waves tend to develop less quantity of IMCs than curled waves. However, the mechanical tests performed did not detect differences that could have been caused by this difference.
- Effect of the flyer material on the interface phenomena in aluminium and copper explosive weldsPublication . Carvalho, G.H.S.F.L.; Mendes, R.; Leal, R. M.; Galvão, I.; Loureiro, A.The effect of physical and mechanical properties of three different flyers on the interface phenomena of partially overlapped explosive welds, using the same base plate material, was studied. Flyers of Copper Cu-DHP and aluminium alloy 6082 (tempers T6 and O) were welded to AA6082-T6 base plates. The morphology of the weld interface is strongly influenced by the physical and mechanical properties of the flyer. In the interface of the aluminiumwelds, the use of a flyer of lower hardness and yield strength than the base plate results in asymmetrical waves, with bigger amplitude and smaller wavelength than the weld series of similar temper, and higher mechanical properties. The copper-aluminium welds presented flat interfaces, mainly because of the significant differences inmelting temperature and density between the copper flyer and the aluminiumbase plate. Considering these results and analysing several dissimilar welds carried out by other authors itwas found thatwhen the product of density and melting temperature ratios between the flyer and the base plate exceeds a certain value, there is no formation of waves at the interface of the metals. Furthermore, for the Cu-Al welds, the CuAl2 (θ) intermetallic phase was formed on the bond zone.
- Effect of friction stir processing parameters on the microstructural and electrical properties of copperPublication . Leal, Rui; Galvão, I.; Loureiro, A.; Rodrigues, D. M.Friction stir processing (FSP) is an innovative technology, based on friction stir welding (FSW) operative principles, which can be used for changing locally the microstructure and the mechanical properties of conventional materials. In this work, the copper alloy C12200 was friction stir processed using two distinct tools, i.e. a scrolled and a conical shoulder tool, in order to promote different thermomechanical conditions inside the stirred volume, and consequently, varied post-processed microstructures. The influence of the tool geometry and tool rotation and traverse speeds on the microstructural and electrical properties of the processed copper alloy was analysed. The processing conditions were found to have an important influence on the electrical conductivity of the processed material. The differences in electrical conductivity were explained based on dislocations density effects. The effect of the dislocations density on electrical conductivity of the processed material was found to prevail over the effect of the grain boundaries.
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