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- 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.
- Copper/stainless steel friction stir spot welds: feasibility and microstructural analysisPublication . Taborda, Diogo; Leal, Rui; Morgado, Teresa; Leitao, Carlos; Galvão, IvanThe possibility of using solid-state joining technologies, such as friction stir welding (FSW) and its variants, to perform dissimilar joints is one of the well know advantages of this class of processes, namely because they are impossible to be produced by other conventional welding processes due to the evident differences in physical and chemical properties of both materials. Relevant advances have been made over the last 20 years in this field. The material pairs that are mostly addressed in the literature are based on systems involving aluminum alloys and other metallic and non-metallic materials. Indeed, with the upgraded interest in this technology concerning specific engineering applications, some specific material combinations such as aluminum-to-copper (Al-Cu) and aluminumto-ferrous alloys (Al-Fe) have become relevant. However, the research about some material pairs is still scarce or inexistent.