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- 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.
- 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.