Browsing by Author "Loureiro, A."
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- Critical review on friction stir welding of aluminium to copperPublication . Galvão, Ivan; Loureiro, A.; Rodrigues, D. M.The status quo of aluminium-to-copper joining by friction stir welding (FSW) drastically changed in recent years, as a result of the increased interest of the scientific community on this subject. Actually, since 2006 a large increase in the number of research groups addressing Al–Cu FSW has been witnessed all over the world, together with a significant increase in the amount of published studies. A chronological perspective on the evolution in Al–Cu FSW research is provided in this work, highlighting the pioneer and original contribution of several researchers to the current knowledge on the subject. Detailed and comprehensive investigations on the material flow mechanisms, the phenomena governing the formation and distribution of intermetallic phases during Al–Cu FSW, their relations with the welding parameters and their impact on the morphological, structural and mechanical properties of the welds are thoroughly discussed. The main findings reported in the literature are summarised in thematic tables.
- Crustal structure across the São Miguel Island (Azores, North Atlantic) and tectonic implicationsPublication . Batista, L.; Hübscher, C.; Terrinha, P.; Matias, L.; Afilhado, Alexandra; Loureiro, A.; Weiß, B.The crustal and uppermost lithospheric mantle of the São Miguel Island in the Azores Plateau was investigated using one 160 km long refraction and wide angle refection seismic profle across the island and the Terceira Rift along with multichan nel seismic refection profles on the top of it. P-wave velocity model shows that São Miguel Island is made up of 5 crustal layers. The sedimentary sequence varies between 150 and 1500 m of thickness and the upper and lower crusts vary from 6 km to maximum thickness of >10 km altogether. The Moho discontinuity lies at 15 km of depth underneath the island and at 11 km outside the island and rift. A 125 km-long layer with a maximum thickness of 2.5 km and Vp of 7.6 km/s is defned at the base of the crust. We speculate that this lens-shaped layer consists of gabbro cumulates formed by magmatic underplating. Extensional southwards directed simple shear across the whole crust and the Moho discontinuity – São Miguel Deep Ductile Deformation Zone – causes uplift, northwards tilting of the island and landslides. Decoupling between ductile deformation in depth and brittle deformation in the shallow levels caused the formation of a rift half-graben flled in with 1500 m of sediments and various mass transport deposits. The São Miguel Deep Ductile Deformation Zone is considered as a difuse plate boundary where deformation is accommodated by brittle mechanisms (seismicity) and plastic fow (lateral thickness variation of the lower crust).
- Deep structure of the Santos basin-São Paulo plateau system, SE BrazilPublication . Evain, M.; Afilhado, Alexandra; Rigoti, C.; Loureiro, A.; Alves, D.; Klingelhoefer, Frauke; Schnurle, Philippe; Feld, Aurelie; Fuck, R; Soares, J.; Lima, M. Vinicius de; Corela, C.; Matias, Luís; Benabdellouahed, M.; Baltzer, A.; Rabineau, Marina; Viana, A.; Moulin, Maryline; Aslanian, DanielThe structure and nature of the crust underlying the Santos Basin-São Paulo Plateau System (SSPS), in the SE Brazilian margin, are discussed based on five wide-angle seismic profiles acquired during the Santos Basin (SanBa) experiment in 2011. Velocity models allow us to precisely divide the SSPS in six domains from unthinned continental crust (Domain CC) to normal oceanic crust (Domain OC). A seventh domain (Domain D), a triangular shape region in the SE of the SSPS, is discussed by Klingelhoefer et al. (2014). Beneath the continental shelf, a similar to 100km wide necking zone (Domain N) is imaged where the continental crust thins abruptly from similar to 40km to less than 15km. Toward the ocean, most of the SSPS (Domains A and C) shows velocity ranges, velocity gradients, and a Moho interface characteristic of the thinned continental crust. The central domain (Domain B) has, however, a very heterogeneous structure. While its southwestern part still exhibits extremely thinned (7km) continental crust, its northeastern part depicts a 2-4km thick upper layer (6.0-6.5km/s) overlying an anomalous velocity layer (7.0-7.8km/s) and no evidence of a Moho interface. This structure is interpreted as atypical oceanic crust, exhumed lower crust, or upper continental crust intruded by mafic material, overlying either altered mantle in the first two cases or intruded lower continental crust in the last case. The deep structure and v-shaped segmentation of the SSPS confirm that an initial episode of rifting occurred there obliquely to the general opening direction of the South Atlantic Central Segment.
- Effect of explosive mixture on quality of explosive welds of copper to aluminiumPublication . Loureiro, A.; Mendes, R.; Ribeiro, J. B.; Leal, R. M.; Galvão, IvanThe aim of this research is to investigate the influence of explosive ratio and type of sensitizer on the quality of explosive welds between copper and aluminium alloy plates. The welds were performed on a partially overlapping joint configuration using an emulsion explosive (EE) with two different sensitizers, hollow glass microspheres (HGMS) and expanded polystyrene spheres (EPS). Welds with an improved surface were achieved by using the HGMS sensitizer. A higher wave amplitude was registered in welds produced with the EPS sensitizer. In turn, the dimension of the molten pockets was influenced by the explosive ratio, increasing in size with increases in the values of this parameter. The intermetallic content of these zones varied according to the sensitizer type. Unlike the CuAl2 phase, the Cu-richer phases CuAl and Cu9Al4 were only identified in welds performed using the EPS sensitizer. An increase in hardness was observed at the interface of all welds, which resulted from both the presence of intermetallic phases and the plastic deformation of the materials promoted by the impact. This effect was most evident on the aluminium alloy side. All the welds had a greater strength than copper, i.e. the weakest material of the joint. (C) 2016 Elsevier Ltd. All rights reserved.
- 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.
- 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.
- 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.