Rui Leal - Academia.edu (original) (raw)

Papers by Rui Leal

Science and Technology of Welding and Joining, Jul 1, 2011

Friction stir welds in 1 mm thick plates of AA 5182-H111 and AA 5083-H111 aluminium alloys are an... more Friction stir welds in 1 mm thick plates of AA 5182-H111 and AA 5083-H111 aluminium alloys are analysed in this paper. The welds were produced using a large range of welding conditions, namely, different process control modes (position and load control), tool parameters (different geometries and dimensions) and process parameters (rotation speed, advancing speed and axial load). Visual inspection and metallographic and mechanical analysis demonstrate that it is possible to obtain consistently good quality welds in very thin plates under a large range of welding conditions. Important relations between base material properties, tool geometry and the final properties of the welds were established.

Microscopy and Microanalysis, Aug 1, 2013

Materials Science Forum, 2010

... 0 50 100 150 200 250 300 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 e (mm/mm) S tre s s (M P a ) Cu1 C... more ... 0 50 100 150 200 250 300 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 e (mm/mm) S tre s s (M P a ) Cu1 Cu2 PC5 Fig. ... [5] Zhang Y, Sato YS, Kokawa H, SHC Park, S. Hirano, Mater. Sci. And Eng. A (2008) 485(1-2), 448-455. [6] T. Saeid, A. Abdollah-zadeh, H. Assadi, F. Ghaini, Mater. Sci. ...

Materials & Design, Apr 1, 2016

The aim of this research is to investigate the influence of explosive ratio and type of sensitize... more The 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 CuAl 2 phase, the Cu-richer phases CuAl and Cu 9 Al 4 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.

Materials in engineering, Jun 1, 2009

In present work friction stir welds produced in 1 mm thick plates of AA 6016-T4 aluminium alloy, ... more In present work friction stir welds produced in 1 mm thick plates of AA 6016-T4 aluminium alloy, with two different tools, were analysed and compared concerning the microstructure and mechanical properties. For each tool, the welding parameters were optimized in order to achieve non-defective welds. Assuming a relation between the welding parameters and the energy input per unit of length of the weld [Seidel TU, Reynolds AP. Visualization of the material flow in AA2195 friction stir welds using a marker insert technique.

Science and Technology of Welding and Joining, Nov 1, 2010

The aim of this investigation was to study the influence of tool geometry on material flow during... more The aim of this investigation was to study the influence of tool geometry on material flow during heterogeneous friction stir welding in 1 mm thick plates of AA 5182-H111 and AA 6016-T4 aluminium alloys. Two types of tool shoulders were used: a shoulder with a conical cavity and a scrolled shoulder. Pin-driven flow was predominant in welds produced with the conical cavity shoulder, which are characterized by an onion ring structure. The interaction between pin-driven and shoulder-driven flow is restricted to the crown of the weld, at the trailing side of the tool, and extends throughout the weld thickness, at the leading side. Although no onion ring structure was formed in welds done with the scrolled shoulder, extensive mixing of the base materials occurred in a plasticized layer flowing through the thickness around the rotating pin. Shoulder-driven flow is intense and continuous around the tool.

Defence Technology, Apr 1, 2023

Materials Characterization, Sep 1, 2019

The influence of an interlayer on the microstructure and the mechanical behaviour of aluminium-ca... more 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.info:eu-repo/semantics/publishedVersio

Ciência & Tecnologia dos Materiais, 2017

Journal of Materials Processing Technology, Sep 1, 2020

Explosive welds of stainless steel and aluminium could only be achieved with the steel positioned... more 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 2 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 timevelocity diagram proved to be a reliable tool to analyse the weldability, especially when used in conjunction with the weldability window.

Design & Narrativas Criativas nos Processos de Prototipagem

Doutor e mestre em ciência e engenharia dos materiais e engenheiro de cerâmica e vidro. Tem exper... more Doutor e mestre em ciência e engenharia dos materiais e engenheiro de cerâmica e vidro. Tem experiência profissional em empresas dos setores químico, matérias primas na área dos minerais não metálicos e industria vidreira. Tem experiência docente de mais de 20 anos em cursos de design industrial, design de produto-cerâmica e vidro e engenharia de produção industrial nomeadamente em unidades curriculares de materiais, processos industriais, inovação de produto e eco-design e design e desenvolvimento sustentável. Tem vários artigos científicos publicados nestas áreas e os seus interesses ao nível da investigação são os materiais e os processos industriais, engenharia de produto, tecnologia vidreira, eco-design e sustentabilidade a inovação de produtos e processos.

Materials

The objective of the current study was to butt-weld 6 mm-thick polyethylene (PE) plates by fricti... more The objective of the current study was to butt-weld 6 mm-thick polyethylene (PE) plates by friction stir welding (FSW) using a non-conventional stationary shoulder tool. The welds were performed with an unheated shoulder and with a shoulder temperature of 85 °C. Additionally, rotational speeds of 870, 1140 and 1500 rpm; welding speeds of 60 and 120 mm/min; and plunge depths of 5.5 and 5.7 mm were used. The influence of these parameters on morphology, hardness, ultimate tensile strength, elongation at break and fracture modes was evaluated. Shoulder heating proved to be crucial for the optimization of PE joints by FSW, as it clearly improved joint efficiency. Furthermore, shoulder heating promoted the reduction in internal and external defects, such as porosity and surface burning. Defect-free weld seams were obtained with higher rotational speeds and a lower welding speed. A maximum joint efficiency of about 97% was achieved with a shoulder temperature of 85 °C, a rotational speed o...

Materials, 2021

Welding is one of the technological fields with the greatest impact in many industries, such as a... more Welding is one of the technological fields with the greatest impact in many industries, such as automotive, aerospace, energy production, electronics, the health sector, etc. [...]

Science and Technology of Welding and Joining, 2017

ABSTRACT The influence of base material properties on the interfacial phenomena in copper and alu... more ABSTRACT The influence of base material properties on the interfacial phenomena in copper and aluminium–copper explosive welds was studied. Two explosive mixtures with different detonation velocities were tested. Sound aluminium–copper joints with effective bonding were achieved by using an explosive mixture with a lower detonation velocity. High energy explosives led to extensive interfacial melting, preventing the production of consistent dissimilar welds. Unlike to the similar copper joints, the aluminium–copper welds presented very asymmetrical interfacial waves, rich in intermetallic phases and displaying a curled morphology. The interaction of the materials in dissimilar welding was found to be completely different depending on the positioning of each alloy in the joint, i.e. positioned as the flyer or as the baseplate.

Materials and Manufacturing Processes, 2019

The 6082 aluminum alloy was welded to copper-DHP by friction stir welding and explosive welding. ... more The 6082 aluminum alloy was welded to copper-DHP by friction stir welding and explosive welding. The effect of each welding process on the microstructural evolution, the intermetallic phases distribution, and the mechanical behavior of both types of welds was analyzed and compared. The microstructural changes proved to be much more expressive in friction stir welding due to the larger area under plastic deformation, the stirring and mixing of the alloys, the longer time under high temperature, and the longer interaction times between the base materials during welding. As explosive welding process is much faster, it avoids extensive microstructural changes and significant interaction of the materials, reducing the intermetallic volumes and their distribution along the interface. The friction stir welds presented Cu-rich intermetallics while the explosive welds presented Al-rich intermetallics. For alloys that can easily form brittle intermetallic phases, excessive interaction during the welding process leads to a very poor mechanical behavior of the joints.

The International Journal of Advanced Manufacturing Technology, 2019

A large number of aluminium-copper explosive welds were produced under different welding conditio... more A large number of aluminium-copper explosive welds were produced under different welding conditions to perform a broad analysis of the weldability of this combination. The influence of the explosive mixture and the relative positioning of the plates on the welding results were analysed. When the aluminium alloy is positioned as the flyer plate, continuous interfacial melting occurred under the low values of energy lost by the collision, and collision point velocity. This proved that the weldability of the aluminium-copper combination is higher when the copper is positioned as the flyer. A mismatch between the experimental results and the existing theories that define the requirements for achieving consistent welds was noticed. Especially for welds produced using the aluminium alloy as the flyer, the experiments proved to be more restrictive than the theories. These theories, despite being widely applied in dissimilar welding literature, present several limitations concerning aluminium-copper welding. New approaches considering the formation of intermetallic phases at the interface, the properties of both welded metals, and/or the difference in their properties should be developed.

Journal of Materials Processing Technology, 2018