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- Friction stir welding and explosive welding of aluminum/copper: process analysisPublication . Carvalho, G. H. S. F. L.; Galvão, Ivan; Mendes, R.; Leal, Rui; Loureiro, AltinoThe 6082 aluminum alloy was welded to copper-DHP by friction stir welding and explosive welding. The effect of each welding process on the microstructural evolution, the intermetallic phases distribution, and the mechanical behavior of both types of welds was analyzed and compared. The microstructural changes proved to be much more expressive in friction stir welding due to the larger area under plastic deformation, the stirring and mixing of the alloys, the longer time under high temperature, and the longer interaction times between the base materials during welding. As explosive welding process is much faster, it avoids extensive microstructural changes and significant interaction of the materials, reducing the intermetallic volumes and their distribution along the interface. The friction stir welds presented Cu-rich intermetallics while the explosive welds presented Al-rich intermetallics. For alloys that can easily form brittle intermetallic phases, excessive interaction during the welding process leads to a very poor mechanical behavior of the joints.
- Influence of base material properties on copper and aluminium-copper explosive weldsPublication . Carvalho, Gustavo; Galvão, Ivan; Mendes, R.; Leal, Rui; Loureiro, AltinoThe 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.
- Weldability of aluminium-copper in explosive weldingPublication . Carvalho, G. H. S. F. L.; Galvão, Ivan; Mendes, R.; Leal, Rui; Loureiro, AltinoA 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 the flyer material on the interface phenomena in aluminium and copper explosive weldsPublication . Carvalho, Gustavo; Mendes, R.; Leal, Rui; Galvão, Ivan; Loureiro, AltinoThe 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 aluminium welds, 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 in melting temperature and density between the copper flyer and the aluminium base plate. Considering these results and analysing several dissimilar welds carried out by other authors it was found that when 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 (theta) intermetallic phase was formed on the bond zone.
- 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; 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.
- Nugget formation and mechanical behaviour of friction stir welds of three dissimilar aluminum alloysPublication . Manuel, Neves; Galvão, Ivan; Leal, Rui; Costa, José D.; Loureiro, AltinoThe aim of this research was to investigate the influence of the properties of the base materials and welding speed on the morphology and mechanical behavior of the friction stir welds of three dissimilar aluminum alloys in a T-joint configuration. The base materials were the AA2017-T4, AA5083-H111, and AA6082-T6 alloys in 3 mm-thick sheets. The AA6082-T6 alloy was the stringer, and the other alloys were located either on the advancing or retreating sides of the skin. All the T-joint welds were produced with a constant tool rotation speed but with different welding speeds. The microstructures of the welds were analyzed using optical microscopy, scanning electron microscopy with energy dispersive spectroscopy, and the electron backscatter diffraction technique. The mechanical properties were assessed according to micro-hardness, tensile, and fatigue testing. Good quality welds of the three dissimilar aluminum alloys could be achieved with friction stir welding, but a high ratio between the tool’s rotational and traverse speeds was required. The welding speed influenced the weld morphology and fatigue strength. The positioning of the skin materials influenced the nugget morphology and the mechanical behavior of the joints. The joints in which the AA2017 alloy was positioned on the advancing side presented the best tensile properties and fatigue strength.
- Nugget formation and mechanical behaviour of friction stir welds of three dissimilar aluminum alloysPublication . Neves, Manuel; Galvão, Ivan; Leal, Rui; Costa, José D.; Loureiro, AltinoThe aim of this research was to investigate the influence of the properties of the base materials and welding speed on the morphology and mechanical behavior of the friction stir welds of three dissimilar aluminum alloys in a T-joint configuration. The base materials were the AA2017-T4, AA5083-H111, and AA6082-T6 alloys in 3 mm-thick sheets. The AA6082-T6 alloy was the stringer, and the other alloys were located either on the advancing or retreating sides of the skin. All the T-joint welds were produced with a constant tool rotation speed but with different welding speeds. The microstructures of the welds were analyzed using optical microscopy, scanning electron microscopy with energy dispersive spectroscopy, and the electron backscatter diffraction technique. The mechanical properties were assessed according to micro-hardness, tensile, and fatigue testing. Good quality welds of the three dissimilar aluminum alloys could be achieved with friction stir welding, but a high ratio between the tool's rotational and traverse speeds was required. The welding speed influenced the weld morphology and fatigue strength. The positioning of the skin materials influenced the nugget morphology and the mechanical behavior of the joints. The joints in which the AA2017 alloy was positioned on the advancing side presented the best tensile properties and fatigue strength.
- Aluminum-to-steel cladding by explosive weldingPublication . Carvalho, Gustavo; Galvão, Ivan; Mendes, Ricardo; Leal, Rui; 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 e_ect 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 di_raction, microhardness and tensile-shear testing with digital image correlation analysis. Although aluminum-carbon steel and aluminum-stainless steel have di_erent 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 di_erence 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.