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Andrade D.G.,University of Coimbra | Galvao I.,University of Coimbra | Galvao I.,Polytechnic Institute of Lisbon | Verdera D.,AIMEN | And 2 more authors.
Science and Technology of Welding and Joining | Year: 2017

The 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. © 2017 Institute of Materials, Minerals and Mining. Published by Taylor & Francis on behalf of the Institute.

Garcia-Diaz A.,AIMEN | Mendez-Rial R.,AIMEN | Preciado M.,University of Glasgow | Souto A.,AIMEN | Harvey A.,University of Glasgow
Optics InfoBase Conference Papers | Year: 2017

We present recent advances on the development of a IR multi aperture imaging system for safety and security surveillance in the context of SEERS project. Besides the development of multi sensor imaging modules using uncooled technology, the research efforts entail embedded algorithms for image reconstruction of multi spectral and super resolution images and image-based measurements as the basis for video analytics. Different use cases are targeted, with a s pecial focus on surveillance of confined traffic and seaports. © 2016 OSA.

Mosquera A.,CSIC - Institute of Materials Science | Mera L.,AIMEN | Fox-Rabinovich G.S.,McMaster University | Azkona I.,Metal Estalki | Endrino J.L.,CSIC - Institute of Materials Science
Nanoscience and Nanotechnology Letters | Year: 2010

Characterization studies involving the fracture behavior of coatings can play an important role in the mechanical analysis of coatings employed in machining applications. In this study, glow discharge optical emission spectroscopy was used to determine the profile composition of various single layer CrAl(Si)N coatings.Nanoimpact tests using a cube corner indenter were compared against standard nanoindentation tests in order to characterize the fracture behavior of the coatings.Micromechanical properties like ductile fracture, brittle fracture, micro hardness, elastic modulus and micro hardness dissipation parameter (MDP) were measured showing that silicon addition in the coatings results in a decrease in ductility. © 2010 American Scientific Publishers.

Rodrigues D.M.,CEMUC | Galvao I.,CEMUC | Gesto D.,AIMEN | Verdera D.,AIMEN
ASM Proceedings of the International Conference: Trends in Welding Research | Year: 2013

The aim of present work was to study the structure and morphology of dissimilar friction stir welds of 1 mm-thick copper-DHP plates to 6 mm-thick AA 5083-H111 aluminum alloy plates. Important relations between the metallurgical and material flow phenomena taking place during Al/Cu welding and the final properties of the welds were established. The base materials interaction revealed to be dependent of the pin length and tool's rotational speed, becoming stronger by increasing these parameters. Nevertheless, although strong base materials interaction has been locally achieved for some welding conditions, sound microstructures were not obtained. Copyright © 2013 ASM International® All rights reserved.

Galvao I.,University of Coimbra | Verdera D.,AIMEN | Gesto D.,AIMEN | Loureiro A.,University of Coimbra | Rodrigues D.M.,University of Coimbra
Journal of Materials Processing Technology | Year: 2013

A heat-treatable (AA 6082) and a non-heat treatable (AA 5083) aluminium alloys were friction stir lap welded to copper using the same welding parameters. Macro and microscopic analysis of the welds enabled to detect important differences in welding results, according to the aluminium alloy type. Whereas important internal defects, resulting from ineffective materials mixing, were detected for the AA 5083/copper welds, a relatively uniform material mixing was detected in the AA 6082/copper welds. Micro-hardness testing and XRD analysis also showed important differences in microstructural evolution for both types of welds. TEM and EBSD-based study of the AA 5083/copper welds revealed the formation of submicron-sized microstructures in the stirred aluminium region, for which untypically high hardness values were registered. © 2013 Elsevier B.V. All rights reserved.

Mira-Aguiar T.,University of Coimbra | Verdera D.,AIMEN | Leitao C.,University of Coimbra | Rodrigues D.M.,University of Coimbra
Journal of Materials Processing Technology | Year: 2016

A Friction Stir Welding (FSW) related technique, which will be labelled Tool Assisted Friction Welding (TAFW), is presented in the current paper. Using this technique, linear lap welding of very thin steel plates is obtained by using a non-consumable columnar tool, with a featureless shoulder, to generate heat by friction with the components to be welded, as in FSW, and also to promote the joining of the plates, under pressure, as in Friction Welding (FW). The joining mechanisms, as well as the thermomechanical conditions developed during welding, will be discussed based on the metallurgical analysis of similar welds produced in two steels: a galvanised low carbon steel (DX51D) and a mild steel (DC01). Mechanical testing, using Digital Image Correlation (DIC) for strain data acquisition, enabled to assess welds strength and plastic properties. The results obtained prove that the TAFW technique enables to obtain very good quality welds, for both base materials, at a very high welding speed and low tool wear/damage. An important influence of the galvanised coating of the DX51D steel on the welding conditions and weld microstructure was also observed. © 2016 Elsevier B.V.

Galvao I.,University of Coimbra | Loureiro A.,University of Coimbra | Verdera D.,AIMEN | Gesto D.,AIMEN | Rodrigues D.M.,University of Coimbra
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science | Year: 2012

In this work, a systematic analysis of the effect of tool offsetting on the morphological, structural, and mechanical properties of 6082-T6 aluminum to copper-DHP friction-stir welds was performed, enabling full understanding of Al-Cu bonding structure and failure mechanisms. Important relations between tool positioning and the thermomechanical phenomena taking place during welding were established. Tool offsetting was revealed to be an effective way of solving one of the most important concerns in Al/Cu friction-stir welding, i.e., the formation of large amounts of intermetallic-rich structures, which deeply influence the final strength and surface morphology of the welds. Actually, for welds produced without tool offsetting, it was found that the formation of fluidized intermetallic-rich structures promote the formation of internal decohesion areas inside the nugget, which have a detrimental effect on weld strength. For welds carried out with tool offsetting, intermetallic formation is almost suppressed, but important metallurgical discontinuities in the vicinity of large copper fragments, dispersed over the nugget, and at the nugget/copper interface were also found to have a detrimental effect on weld strength. © 2012 The Minerals, Metals & Materials Society and ASM International.

Costa M.I.,University of Coimbra | Verdera D.,AIMEN | Costa J.D.,University of Coimbra | Leitao C.,University of Coimbra | Rodrigues D.M.,University of Coimbra
Journal of Materials Processing Technology | Year: 2015

The influence of pin geometry and process parameters on the morphology and strength of friction stir lap welds, in very thin sheets, is analysed. The base material is the AA5754-H22 work hardened aluminium alloy. Three different pin geometries were tested, one cylindrical and two conical, with different taper angles. For each pin geometry, varying welding speeds, ranging from 350 to 1000 mm/min, were tested in order to simultaneously weld properties and process productivity. Weld defects assessment was performed using metallographic analyses. strength was by performing mechanical tests both monotonic and cyclic loading conditions. Monotonic tests included performing transverse and lap tensile-shear tests. Strain data acquisition using Digital Image Correlation (DIC) enabled to determine local weld properties as the joints failure mode monotonic loading. The results show that the use of unthreaded conical pin tools, with a low shoulder/pin diameter relation, is the more suitable solution for the production of good quality welds. Irrespective of the pin geometry, very high joint strength efficiencies (close to 90%) were obtained when loading the retreating side of the welds. It is also shown that good quality welds may be produced at very high welding speeds. © 2015 Elsevier B.V. All rights reserved.

Costa M.I.,University of Coimbra | Verdera D.,AIMEN | Leitao C.,University of Coimbra | Rodrigues D.M.,University of Coimbra
Materials and Design | Year: 2015

Dissimilar friction stir welding (FSW) of heat (AA 6082-T6) and non-heat (AA 5754-H22) treatable aluminium alloys, in lap joint configuration, was performed in this work. The base material plates were 1. mm thick. Welds were performed combining different plates positioning, relative to the tool shoulder, in order to assess the influence of base materials properties on welds strength. Three different tools were tested, one cylindrical and two conical, with different taper angles. Welds strength was characterized by performing transverse and tensile-shear tests. Strain data acquisition by Digital Image Correlation (DIC) was used to determine local weld properties. The results obtained enabled to conclude that the dissimilar welds strength is strongly dependent on the presence of the well-known hooking defect and that the hooking characteristics are strongly conditioned by base materials properties/positioning. By placing the AA 6082-T6 alloy, as top plate, in contact with the tool shoulder, superior weld properties are achieved independently of the tool geometry. It is also concluded that the use of unthreaded conical pin tools, with a low shoulder/pin diameter relation, is the most suitable solution for the production of welds with similar strengths for advancing and retreating sides. © 2015 Elsevier Ltd.

Casal J.M.,University of Vigo | Porteiro J.,University of Vigo | Miguez J.L.,University of Vigo | Vazquez A.,AIMEN
Applied Thermal Engineering | Year: 2015

Abstract This study presents a new modelling methodology for three-dimensional simulation of a reheating furnace of steel billets with natural gas burners. The movement of the billets inside the furnace is a periodically transient phenomenon. A modification in the energy transport equation is introduced through source terms in the billet region to convert the transient movements of the billets into a steady-state simulation, which significantly reduces the computational time without any loss of information. The combustion simulation inside the burners is performed using a global combustion mechanism that takes into account the combustion of the main gaseous species present in natural gas following a kinetic and turbulent control of the reaction through the Eddy Dissipation Concept (EDC). The results are contrasted and validated with the data obtained in a real facility though the SCADA of the plant. Some parameters, such as the surface temperatures of billets at the outlet and the distribution of power supplied by the fuel inside the furnace are reasonably close to the real case data obtained in temperature fields of both billets and the gas phase as well as the energy balance, leading to the conclusion that the proposed methodology is adequate for the purpose of simulating this system. © 2015 Elsevier Ltd.

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