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- Influence of softening mechanisms on base materials plastic behaviour and defects formation in friction stir lap weldingPublication . S, SREE; Galvão, Ivan; Leitao, Carlos; Rodrigues, DulceThe AA6082-T6 and AA5754-H22 aluminium alloys were selected as the base materials to fabricate similar and dissimilar friction stir lap welds. Three lap configurations, AA6082/AA5754, AA5754/AA6082 and AA6082/AA6082, were produced using three pin profiles and tested to analyse the role of the plastic behaviours of the base materials on the welding conditions. The macrostructural characterisation was carried out to understand the material flow response and hook defect formation. The mechanical characterisation of the joints was done by microhardness and lap tensile shear testing. The finite element analysis and phase simulation were conducted to predict the phase dissolution temperatures and the softening kinetics. The welding torque and axial forces registered were analysed to quantify differences in the alloy’s flowability during welding. The analysis of the welding machine outputs enabled to conclude that higher axial forces were registered when the AA5754 alloy was placed at the top of the dissimilar lap joint, showing that the non-heat-treatable alloy has lower flowability than the heat-treatable alloy. These results were associated with the flow-softening of the AA6082 alloy in plastic deformation at high temperatures. The coupled experimental and numerical analysis revealed that the plastic behaviour of the base materials strongly influenced the material flow and, in this way, the hook defect formation and the shear tensile properties of the welds.
- Influence of the structure and phase composition of the bond interface on aluminium-copper lap welds strengthPublication . Andrade, David; Galvão, Ivan; Verdera, David; Leitao, Carlos; Rodrigues, DulceThe 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.
- 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.