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Formation of intermetallic structures at the interface of steel-to-aluminium explosive welds

Publication . Carvalho, Gustavo; Galvão, Ivan; Mendes, R.; Leal, Rui; Loureiro, A.

The formation of intermetallic structures at the interface of carbon steel to 6082 aluminium alloy explosive welds and their influence on the weldability of these two materials were studied. The morphology, the microstructure, the chemical and phase compositions of the welds were characterised by several types of microscopy techniques. The interface characterisation proved that explosive mixtures with a lower detonation velocity were revealed as being more suitable for achieving consistent welds since jet entrapment was prevented and continuous molten layers were not formed at the weld interface. It was also found that the physical properties of the intermetallic phases generated at the weld interface have a strong influence on the weldability of steel-to-aluminium explosive welds. Specifically, it was shown that the formation of aluminium-rich intermetallic phases at the weld interface increases the solidification time of the interfacial molten material, decreasing the weldability of these two materials. The formation of these intermetallic compounds should be avoided by reducing the interaction between the flyer and the baseplate as well as by avoiding excessive molten layers.

2018-08Journal article

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Influence of the structure and phase composition of the bond interface on aluminium-copper lap welds strength

Publication . Andrade, David; Galvão, Ivan; Verdera, David; Leitao, Carlos; Rodrigues, Dulce

The structure and phase composition of the bond interface of aluminium-copper lap welds produced by friction stir welding and tool-assisted friction welding were analysed. Microstructural analysis proved that no through-interface material flow took place in tool-assisted friction welding and that aluminium-copper joining resulted from the formation of a thin and continuous intermetallic layer at the lap interface. For the welds produced by friction stir welding, evidences of through-interface material flow were found, promoting mechanical interlocking of both base materials, at the lap interface, and formation of discontinuous intermetallic layers. Mechanical testing showed that the tool-assisted friction welds, with excellent surface finishing, had low strength, contrary to the friction stir welds, which displayed excellent bond strength. The comparison of the mechanical and microstructural results, for both weld types, pointed to the ineffectiveness of the continuous intermetallic layer in providing high strength bonding.

2018Journal article

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Influence of base material properties on copper and aluminium-copper explosive welds

Publication . Carvalho, Gustavo; Galvão, Ivan; Mendes, R.; Leal, Rui; Loureiro, Altino

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.

2018Journal article

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Effect of the flyer material on the interface phenomena in aluminium and copper explosive welds

Publication . Carvalho, Gustavo; Mendes, R.; Leal, Rui; Galvão, Ivan; Loureiro, Altino

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 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.

2017-05-15Journal article

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Weldability of aluminium-copper in explosive welding

Publication . Carvalho, G. H. S. F. L.; Galvão, Ivan; Mendes, R.; Leal, Rui; Loureiro, Altino

A 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.

2019-08Journal article

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