Ahmed Elrefaey | Swansea University (original) (raw)

Papers by Ahmed Elrefaey

Engineering Failure Analysis, 2021

Thousands of lead anodes are currently used in the electro-winning of copper across the globe. Th... more Thousands of lead anodes are currently used in the electro-winning of copper across the globe. The corrosion and the electrochemical performance of these anodes significantly affect the economy of the process. Premature failure of anodes is often a problem for the commercial operators of tank houses. Recently, the authors were asked to advise on an unusual case where a lead alloy anode split at almost the centreline of the cross section. Different characterization techniques were employed to detect the cause of failure. The fractured samples were metallographically examined with an optical microscope and a Scanning Electron Microscope (SEM) equipped with Energy-Dispersive X-ray Spectroscopy (EDS) analysis. Different phase at the fracture surface were also identified by X-Ray Diffraction technique. The failure mechanism of this anode appears to be manganese contaminated electrolyte attacking the anode perimeter, leading to initial corrosion sites and compounded by subsequent exfoliation corrosion through inter-granular attack and further formation of manganese dioxide. The established practice of producing lead alloy anodes via rolling confers beneficial properties to the finished anodes. However, the resulting elongated grains can in some cases, where the electrolyte is contaminated with elements that are prejudicial to stable oxide layer formation, cause susceptibility to exfoliation corrosion.

Acta Metallurgica Sinica (English Letters), 2015

Integrating structures made from aluminum alloys in automotive industry requires a large amount o... more Integrating structures made from aluminum alloys in automotive industry requires a large amount of joining. As a consequence, the properties of the joints have a significant influence on the overall performance of the whole structure. Robot cold metal transfer welding is a relatively new joining technique and has been used in this work to join 6082-T4 and 5182-O aluminum alloy sheets by using ER5356 and ER4043 filler metals. Microstructure characterization was performed by optical microscopy and energy dispersive X-ray spectroscopy, and the mechanical properties were measured by tensile and hardness tests. A correlation is made between welding variables, mechanical properties and the microstructure of welded joints. Results indicate that robot cold metal transfer welding provides good joint efficiency with high welding speed, good tensile strength, and ductility. Owing to the low heat input of robot cold metal transfer welding process, the heat affected zone microstructure was quite...

Transactions of JWRI, 2000

Journal of Materials Science

Acta Metallurgica Sinica (English Letters), 2015

Journal of Materials Processing Technology, 2014

Anodically bonded glass/titanium and glass/steel were investigated for applications in a variety ... more Anodically bonded glass/titanium and glass/steel were investigated for applications in a variety of industrial sectors. Residual stresses that build up during the bonding or cooling down of a joint to room temperature represent the main challenge to the joining process since they drastically weaken the mechanical strength of the joint. A layer of liquid tin-based solder in between the glass and metal part of the joint is used to reduce the internal stresses and improve the contact between the surfaces. The microstructural characterization of glass/solder/titanium and glass/solder/steel joints formed from Ni coated metal substrates indicated that Ni 3 Sn 4 was formed for both types of joint but with a different morphology and location depending on the type of metal substrate. The average shear strength of the joints was 24 MPa for glass-titanium and 21 MPa for glass-steel joints. For both types of joint, the fracture crack propagated along the glass-solder interface.

Materialwissenschaft und Werkstofftechnik, 2010

ABSTRACT The joining technology of dissimilar lightweight materials between metals and polymer is... more ABSTRACT The joining technology of dissimilar lightweight materials between metals and polymer is essential for realizing cars with hybrid structures and for other engineering applications. These types of joints are still difficult to generate and their behaviour is not fully understood. Laser welding offers specific process advantages over conventional technologies, such as short process times, while providing optically and qualitatively valuable weld seams and imposing minimal thermal stress. Furthermore, the process is compatible with automation. This paper summarizes the efforts to attain suitable joint strengths with the stainless steel plate type S30400 and a Polyethylene Terephtalate Glycol (PETG) plastic sheet. The study considers the optimization of two important process parameters, namely laser power, and welding speed. Microstructure features, test of tensile shear strength, investigation of the fracture location, and morphology were used to evaluate the joint performance. The result indicates that there is an optimum value for laser power, which achieves a sufficient melting and heat transfer to the joint without decomposing the plastic sheet and hence, enables to obtain high joint strength. Moreover, a low welding speed is preferable in most combinations of welding parameters since it achieves an adequate melting and wetting of the polymer to the steel surface.Das Fügen der artungleichen Leichtbauwerkstoffe Metall und Kunststoff ist im hybriden Automobilbau wie auch anderen Ingenieursanwendungen essentiell. Derartige Fügeverbunde sind immer noch schwierig umsetzbar und ihr Verhalten ist noch nicht vollständig erforscht. Laserstrahlschweißen bietet gegenüber konventionellen Verfahren prozessspezifische Vorteile wie kurze Taktzeiten bei gleichzeitig optisch wie qualitativ hochwertigen Schweißnähten und geringen thermisch induzierten Eigenspannungen. Weiterhin ist der Prozess leicht automatisierbar. In den vorliegenden Untersuchungen wurden der Stahl S30400 und Polyethylene Terephtalate Glycol (PETG) erfolgreich gefügt und moderate Festigkeiten wurden erzielt. Innerhalb der Untersuchungen wurde der Einfluss der beiden wichtigsten Prozessparameter, die Laserleistung und die Verfahrgeschwindigkeit, analysiert. Die Mikrostruktur, Scherzugfestigkeit, Bruchfläche und Morphologie wurden untersucht, um die Verbundperformance zu bewerten. Die Ergebnisse zeigen, dass es ein Optimum für die Laserleistung gibt, die eine ausreichende Aufschmelzung und Wärmeleitung in der Fügezone sicher stellt, ohne den Kunststoff zu zersetzen und führt somit zu einer hohen Festigkeit. Darüber hinaus ist eine geringe Schweißgeschwindigkeit vorzuziehen, da sie ein adäquates Aufschmelzen und Benetzen des Polymers auf der Stahloberfläche erlaubt.

Materials Science and Engineering: A, 2013

ABSTRACT In this study, the evolution of the interfacial microstructure, hardness distribution, a... more ABSTRACT In this study, the evolution of the interfacial microstructure, hardness distribution, and the joint strength of vacuum brazed commercially pure titanium were evaluated. A thin nickel layer, with different thicknesses, was deposited by PVD technique to serve as the brazing filler metal. Test joints were processed at temperatures of 910 °C and 960 °C using a soaking time of 15 and 90 min. The experimental results showed that sound joints with a good wetting quality as well as lack of pores and cracks can be achieved at a brazing temperature of 960 °C. A Ti2Ni intermetallic compound was formed at the interfacial area at a soaking time of 15 min and with a deposition rate of 90 AH which was detrimental to the joint mechanical properties. Meanwhile, at a soaking time of 90 min, intermetallic compound was not detected and the diffusion of nickel was completed at all deposition rates which improve the shear strength of the joints.

Journal of Materials Processing Technology, 2009

Dissimilar titanium/steel metals were successfully joined by diffusion bonding process with the h... more Dissimilar titanium/steel metals were successfully joined by diffusion bonding process with the help of a copper-based interlayer. The appropriate processing parameters have been investigated and the joints were analyzed by means of scanning electron microscopy (SEM), microhardness measurement, shear strength test, and X-ray diffractometry (XRD). The results show that the joint could not be bonded at a temperature lower than

Journal of Materials Engineering and Performance, 2005

The welding of a lap joint of a commercially pure aluminum plate to a low carbon steel plate (i.e... more The welding of a lap joint of a commercially pure aluminum plate to a low carbon steel plate (i.e., Al plate top, and steel plate bottom) was produced by friction stir welding using various rotations and traveling speeds of the tool to investigate the effects of the welding parameters on the joint strength. The joint strength depended strongly on the

International Journal of Pressure Vessels and Piping

Dissimilar metal welds are necessary in high-pressure subsea systems and in cases where forged co... more Dissimilar metal welds are necessary in high-pressure subsea systems and in cases where forged components must be welded to pipelines. F22 (2.25Cr-1Mo) steel is often used in such forged steel components and, since this steel cannot enter service without undergoing post-weld heat treatment (PWHT), the components are usually prepared for field welds through the application of a buttering layer. Furthermore, a weld overlay is deposited for the purpose of mitigating corrosion. This combination of multiple welding tasks and dissimilar materials leads to the possibility of developing substantial residual stresses. This study aims to provide insights to the evolution of residual stresses at each stage of the welding operation. The assessment has been undertaken on laboratory-scale weld mock-ups using the contour method for residual stress measurement, and incremental centre hole drilling. It was found that both buttering and cladding introduce near-yield levels of tensile residual stresses, but that these stresses are successfully relieved upon PWHT.

Metallurgical and Materials Transactions A, 2007

The lap joint of a commercially pure titanium plate (CP Ti) to a low-carbon steel plate was produ... more The lap joint of a commercially pure titanium plate (CP Ti) to a low-carbon steel plate was produced with a vacuum-brazed furnace using a silver-based filler alloy at different temperatures and lap widths in order to investigate the effects of such brazing parameters on the joint strength and structure. It was found that the shear strength of brazed joints depends

Materialwissenschaft und …, 2010

... Bild 6. Gefügeausprägungen von Titan/Stahl-Verbunden nach Poten-ziodynamischen Polarisationsv... more ... Bild 6. Gefügeausprägungen von Titan/Stahl-Verbunden nach Poten-ziodynamischen Polarisationsversuchen: (a) Bei 8508C für 15 min gelöteter Verbund, (b) Bei 8808C für 15 min gelöteter Verbund, (c) Bei 9308C für 15 min gelöteter ... [3] S. Kundu, M. Ghosh, S. Chatterjee ...

International Journal of Pressure Vessels and Piping

In oil and gas and other industries, valve bodies are often manufactured using a 2.25Cr-1Mo steel... more In oil and gas and other industries, valve bodies are often manufactured using a 2.25Cr-1Mo steel which, if welded, requires post-weld heat treatment (PWHT) in order to restore toughness. The safe operation and long-term integrity of such welds is critically dependent on achieving adequate toughness across the welded joint. In this work, mock-ups were manufactured for the purpose of assessing the effects of the weld heat input on toughness. The assessment was made by carrying out crack tip opening displacement (CTOD) and Charpy-impact tests in different metallurgical regions and, after testing, by examining the fracture surfaces using optical-and scanning-electron microscopy, and energy-dispersive spectroscopy. There did not appear to be an effect of weld heat input on toughness at a test temperature of +20°C. However, for the case where a high weld heat input was employed, the toughness of the weld metal dropped by close to 50% when the temperature was decreased to -20°C. These results suggest that inadequate control of the welding process may lead to significant variability in weld toughness, and that high weld heat inputs should be avoided when welding or buttering 2.25Cr-1Mo steel components.

Transactions of Jwri, Dec 1, 2000

Journal of Materials Processing Technology, 2009

... Low temperature aluminium-based filler metals could be a good choice in this regard. ... at t... more ... Low temperature aluminium-based filler metals could be a good choice in this regard. ... at the interfacial layer resulting in isothermal solidification as in the case of transient liquid phasebonding. ... except at the interface with titanium substrate which supports its partial melting at the ...

5th International Brazing and Soldering Conference, 2012

ABSTRACT Aluminum and steel are the most frequently applied construction materials. They feature ... more ABSTRACT Aluminum and steel are the most frequently applied construction materials. They feature well known and complementary material properties and are increasingly used in dissimilar material structures. Hence, it is major importance to provide appropriate joining techniques in order to exploit the full potential of these hybrid structures. An auspicious approach for the manufacturing of aluminum-steel joints is TLP brazing. Due to moderate process temperatures and controlled diffusion within the joint area, the formation of brittle intermetallics such as Fe2Al5 can be prevented to the lowest possible extent. Within these investigations copper layers has been applied by means of PVD coating on both joining partners, which form a liquid phase with aluminum at 548°C and therefore allow brazements at 580°C. Additionally, diffusion barriers consisting of nickel or titanium were deposited onto the steel in order to decrease the generation of iron aluminides, which initiate cracks due to their immanent brittleness and thus force a premature fracture of the joints. In this regard, nickel as a diffusion barrier shows no significant improvement regarding the joint microstructure compared to copper single layers, whereas joints containing titanium interlayers feature very thin layers of intermetallic precipitates (less than 3 µm) even at high dwell times.

Engineering Failure Analysis, 2021

Thousands of lead anodes are currently used in the electro-winning of copper across the globe. Th... more Thousands of lead anodes are currently used in the electro-winning of copper across the globe. The corrosion and the electrochemical performance of these anodes significantly affect the economy of the process. Premature failure of anodes is often a problem for the commercial operators of tank houses. Recently, the authors were asked to advise on an unusual case where a lead alloy anode split at almost the centreline of the cross section. Different characterization techniques were employed to detect the cause of failure. The fractured samples were metallographically examined with an optical microscope and a Scanning Electron Microscope (SEM) equipped with Energy-Dispersive X-ray Spectroscopy (EDS) analysis. Different phase at the fracture surface were also identified by X-Ray Diffraction technique. The failure mechanism of this anode appears to be manganese contaminated electrolyte attacking the anode perimeter, leading to initial corrosion sites and compounded by subsequent exfoliation corrosion through inter-granular attack and further formation of manganese dioxide. The established practice of producing lead alloy anodes via rolling confers beneficial properties to the finished anodes. However, the resulting elongated grains can in some cases, where the electrolyte is contaminated with elements that are prejudicial to stable oxide layer formation, cause susceptibility to exfoliation corrosion.

Acta Metallurgica Sinica (English Letters), 2015

Integrating structures made from aluminum alloys in automotive industry requires a large amount o... more Integrating structures made from aluminum alloys in automotive industry requires a large amount of joining. As a consequence, the properties of the joints have a significant influence on the overall performance of the whole structure. Robot cold metal transfer welding is a relatively new joining technique and has been used in this work to join 6082-T4 and 5182-O aluminum alloy sheets by using ER5356 and ER4043 filler metals. Microstructure characterization was performed by optical microscopy and energy dispersive X-ray spectroscopy, and the mechanical properties were measured by tensile and hardness tests. A correlation is made between welding variables, mechanical properties and the microstructure of welded joints. Results indicate that robot cold metal transfer welding provides good joint efficiency with high welding speed, good tensile strength, and ductility. Owing to the low heat input of robot cold metal transfer welding process, the heat affected zone microstructure was quite...

Transactions of JWRI, 2000

Journal of Materials Science

Acta Metallurgica Sinica (English Letters), 2015

Journal of Materials Processing Technology, 2014

Anodically bonded glass/titanium and glass/steel were investigated for applications in a variety ... more Anodically bonded glass/titanium and glass/steel were investigated for applications in a variety of industrial sectors. Residual stresses that build up during the bonding or cooling down of a joint to room temperature represent the main challenge to the joining process since they drastically weaken the mechanical strength of the joint. A layer of liquid tin-based solder in between the glass and metal part of the joint is used to reduce the internal stresses and improve the contact between the surfaces. The microstructural characterization of glass/solder/titanium and glass/solder/steel joints formed from Ni coated metal substrates indicated that Ni 3 Sn 4 was formed for both types of joint but with a different morphology and location depending on the type of metal substrate. The average shear strength of the joints was 24 MPa for glass-titanium and 21 MPa for glass-steel joints. For both types of joint, the fracture crack propagated along the glass-solder interface.

Materialwissenschaft und Werkstofftechnik, 2010

ABSTRACT The joining technology of dissimilar lightweight materials between metals and polymer is... more ABSTRACT The joining technology of dissimilar lightweight materials between metals and polymer is essential for realizing cars with hybrid structures and for other engineering applications. These types of joints are still difficult to generate and their behaviour is not fully understood. Laser welding offers specific process advantages over conventional technologies, such as short process times, while providing optically and qualitatively valuable weld seams and imposing minimal thermal stress. Furthermore, the process is compatible with automation. This paper summarizes the efforts to attain suitable joint strengths with the stainless steel plate type S30400 and a Polyethylene Terephtalate Glycol (PETG) plastic sheet. The study considers the optimization of two important process parameters, namely laser power, and welding speed. Microstructure features, test of tensile shear strength, investigation of the fracture location, and morphology were used to evaluate the joint performance. The result indicates that there is an optimum value for laser power, which achieves a sufficient melting and heat transfer to the joint without decomposing the plastic sheet and hence, enables to obtain high joint strength. Moreover, a low welding speed is preferable in most combinations of welding parameters since it achieves an adequate melting and wetting of the polymer to the steel surface.Das Fügen der artungleichen Leichtbauwerkstoffe Metall und Kunststoff ist im hybriden Automobilbau wie auch anderen Ingenieursanwendungen essentiell. Derartige Fügeverbunde sind immer noch schwierig umsetzbar und ihr Verhalten ist noch nicht vollständig erforscht. Laserstrahlschweißen bietet gegenüber konventionellen Verfahren prozessspezifische Vorteile wie kurze Taktzeiten bei gleichzeitig optisch wie qualitativ hochwertigen Schweißnähten und geringen thermisch induzierten Eigenspannungen. Weiterhin ist der Prozess leicht automatisierbar. In den vorliegenden Untersuchungen wurden der Stahl S30400 und Polyethylene Terephtalate Glycol (PETG) erfolgreich gefügt und moderate Festigkeiten wurden erzielt. Innerhalb der Untersuchungen wurde der Einfluss der beiden wichtigsten Prozessparameter, die Laserleistung und die Verfahrgeschwindigkeit, analysiert. Die Mikrostruktur, Scherzugfestigkeit, Bruchfläche und Morphologie wurden untersucht, um die Verbundperformance zu bewerten. Die Ergebnisse zeigen, dass es ein Optimum für die Laserleistung gibt, die eine ausreichende Aufschmelzung und Wärmeleitung in der Fügezone sicher stellt, ohne den Kunststoff zu zersetzen und führt somit zu einer hohen Festigkeit. Darüber hinaus ist eine geringe Schweißgeschwindigkeit vorzuziehen, da sie ein adäquates Aufschmelzen und Benetzen des Polymers auf der Stahloberfläche erlaubt.

Materials Science and Engineering: A, 2013

ABSTRACT In this study, the evolution of the interfacial microstructure, hardness distribution, a... more ABSTRACT In this study, the evolution of the interfacial microstructure, hardness distribution, and the joint strength of vacuum brazed commercially pure titanium were evaluated. A thin nickel layer, with different thicknesses, was deposited by PVD technique to serve as the brazing filler metal. Test joints were processed at temperatures of 910 °C and 960 °C using a soaking time of 15 and 90 min. The experimental results showed that sound joints with a good wetting quality as well as lack of pores and cracks can be achieved at a brazing temperature of 960 °C. A Ti2Ni intermetallic compound was formed at the interfacial area at a soaking time of 15 min and with a deposition rate of 90 AH which was detrimental to the joint mechanical properties. Meanwhile, at a soaking time of 90 min, intermetallic compound was not detected and the diffusion of nickel was completed at all deposition rates which improve the shear strength of the joints.

Journal of Materials Processing Technology, 2009

Dissimilar titanium/steel metals were successfully joined by diffusion bonding process with the h... more Dissimilar titanium/steel metals were successfully joined by diffusion bonding process with the help of a copper-based interlayer. The appropriate processing parameters have been investigated and the joints were analyzed by means of scanning electron microscopy (SEM), microhardness measurement, shear strength test, and X-ray diffractometry (XRD). The results show that the joint could not be bonded at a temperature lower than

Journal of Materials Engineering and Performance, 2005

The welding of a lap joint of a commercially pure aluminum plate to a low carbon steel plate (i.e... more The welding of a lap joint of a commercially pure aluminum plate to a low carbon steel plate (i.e., Al plate top, and steel plate bottom) was produced by friction stir welding using various rotations and traveling speeds of the tool to investigate the effects of the welding parameters on the joint strength. The joint strength depended strongly on the

International Journal of Pressure Vessels and Piping

Dissimilar metal welds are necessary in high-pressure subsea systems and in cases where forged co... more Dissimilar metal welds are necessary in high-pressure subsea systems and in cases where forged components must be welded to pipelines. F22 (2.25Cr-1Mo) steel is often used in such forged steel components and, since this steel cannot enter service without undergoing post-weld heat treatment (PWHT), the components are usually prepared for field welds through the application of a buttering layer. Furthermore, a weld overlay is deposited for the purpose of mitigating corrosion. This combination of multiple welding tasks and dissimilar materials leads to the possibility of developing substantial residual stresses. This study aims to provide insights to the evolution of residual stresses at each stage of the welding operation. The assessment has been undertaken on laboratory-scale weld mock-ups using the contour method for residual stress measurement, and incremental centre hole drilling. It was found that both buttering and cladding introduce near-yield levels of tensile residual stresses, but that these stresses are successfully relieved upon PWHT.

Metallurgical and Materials Transactions A, 2007

The lap joint of a commercially pure titanium plate (CP Ti) to a low-carbon steel plate was produ... more The lap joint of a commercially pure titanium plate (CP Ti) to a low-carbon steel plate was produced with a vacuum-brazed furnace using a silver-based filler alloy at different temperatures and lap widths in order to investigate the effects of such brazing parameters on the joint strength and structure. It was found that the shear strength of brazed joints depends

Materialwissenschaft und …, 2010

... Bild 6. Gefügeausprägungen von Titan/Stahl-Verbunden nach Poten-ziodynamischen Polarisationsv... more ... Bild 6. Gefügeausprägungen von Titan/Stahl-Verbunden nach Poten-ziodynamischen Polarisationsversuchen: (a) Bei 8508C für 15 min gelöteter Verbund, (b) Bei 8808C für 15 min gelöteter Verbund, (c) Bei 9308C für 15 min gelöteter ... [3] S. Kundu, M. Ghosh, S. Chatterjee ...

International Journal of Pressure Vessels and Piping

In oil and gas and other industries, valve bodies are often manufactured using a 2.25Cr-1Mo steel... more In oil and gas and other industries, valve bodies are often manufactured using a 2.25Cr-1Mo steel which, if welded, requires post-weld heat treatment (PWHT) in order to restore toughness. The safe operation and long-term integrity of such welds is critically dependent on achieving adequate toughness across the welded joint. In this work, mock-ups were manufactured for the purpose of assessing the effects of the weld heat input on toughness. The assessment was made by carrying out crack tip opening displacement (CTOD) and Charpy-impact tests in different metallurgical regions and, after testing, by examining the fracture surfaces using optical-and scanning-electron microscopy, and energy-dispersive spectroscopy. There did not appear to be an effect of weld heat input on toughness at a test temperature of +20°C. However, for the case where a high weld heat input was employed, the toughness of the weld metal dropped by close to 50% when the temperature was decreased to -20°C. These results suggest that inadequate control of the welding process may lead to significant variability in weld toughness, and that high weld heat inputs should be avoided when welding or buttering 2.25Cr-1Mo steel components.

Transactions of Jwri, Dec 1, 2000

Journal of Materials Processing Technology, 2009

... Low temperature aluminium-based filler metals could be a good choice in this regard. ... at t... more ... Low temperature aluminium-based filler metals could be a good choice in this regard. ... at the interfacial layer resulting in isothermal solidification as in the case of transient liquid phasebonding. ... except at the interface with titanium substrate which supports its partial melting at the ...

5th International Brazing and Soldering Conference, 2012

ABSTRACT Aluminum and steel are the most frequently applied construction materials. They feature ... more ABSTRACT Aluminum and steel are the most frequently applied construction materials. They feature well known and complementary material properties and are increasingly used in dissimilar material structures. Hence, it is major importance to provide appropriate joining techniques in order to exploit the full potential of these hybrid structures. An auspicious approach for the manufacturing of aluminum-steel joints is TLP brazing. Due to moderate process temperatures and controlled diffusion within the joint area, the formation of brittle intermetallics such as Fe2Al5 can be prevented to the lowest possible extent. Within these investigations copper layers has been applied by means of PVD coating on both joining partners, which form a liquid phase with aluminum at 548°C and therefore allow brazements at 580°C. Additionally, diffusion barriers consisting of nickel or titanium were deposited onto the steel in order to decrease the generation of iron aluminides, which initiate cracks due to their immanent brittleness and thus force a premature fracture of the joints. In this regard, nickel as a diffusion barrier shows no significant improvement regarding the joint microstructure compared to copper single layers, whereas joints containing titanium interlayers feature very thin layers of intermetallic precipitates (less than 3 µm) even at high dwell times.