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- Explosive welding of aluminium to stainless steel using carbon steel and niobium interlayersPublication . Carvalho, Gustavo; Galvão, Ivan; Mendes, R.; Leal, R. M.; Loureiro, AltinoThis 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.
- Formation of intermetallic structures at the interface of steel-to-aluminium explosive weldsPublication . 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.
- 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.
- Explosive welding of aluminium to stainless steelPublication . Carvalho, Gustavo; Galvão, Ivan; Mendes, R.; Leal, Rui; Loureiro, A.Explosive welds of stainless steel and aluminium could only be achieved with the steel positioned as the baseplate. Using stainless steel as the flyer plate, the tensile stresses arrive at the interface before the complete solidification of the localised melting and no bonding is achieved. The poor weldability in this configuration is mainly related to the very low thermal conductivity of the flyer compared to the baseplate. The position of the materials significantly influences the weldability, and the ideal material for the flyer should have a higher melting temperature, specific heat and thermal conductivity, and a lower density compared to the baseplate. Some intermetallic formation is inevitable in dissimilar welds of combinations that can easily form intermetallic phases. The time-velocity diagram proved to be a reliable tool to analyse the weldability, especially when used in conjunction with the weldability window.
- Microstructure and mechanical behaviour of aluminium-carbon steel and aluminium-stainless steel clads produced with an aluminium interlayerPublication . Carvalho, G. H. S. F. L.; Galvão, Ivan; Mendes, R.; Leal, Rui; Loureiro, A.The influence of an interlayer on the microstructure and the mechanical behaviour of aluminium-carbon steel and aluminium-stainless steel clads produced by explosive welding was studied. Different series of welds were produced both with and without an aluminium interlayer, testing different welding parameters. The combination of aluminium to carbon steel presented a better weldability than aluminium to stainless steel. For both couples, low-velocity welds presented the best microstructure and mechanical strength. The mechanical tests showed that the aluminium to carbon steel joining did not benefit from the use of the interlayer. A joint with good interfacial morphology and excellent tensile-shear properties was achieved by low-velocity direct welding, with the fracture occurring outside the joining region. For the aluminium to stainless steel couple, the use of the interlayer increased its weldability. However, the mechanical strength of the joint is restricted by the low strength of the interlayer. The presence of intermetallic compounds at the weld interface, does not, by itself, promote the poor-quality of the explosive weld. The way the interface accommodates and distributes these intermetallics dictates the weld's quality.