Alexander Galloway

University of Strathclyde · Department of Mechanical and Aerospace Engineering

Inconel 625 is a nickel-based superalloy widely used in industries such as energy, space, and defence, due to its strength and corrosion resistance. It is traditionally time- and resource-intensive to machine, leading to increased environmental impact and material waste. Using additive manufacturing (AM) technology enables a reduction in resource c...

Precipitation hardening (PH) stainless steels, such as 15-5PH, have a high strength combined with excellent corrosion resistance. These properties make them valuable in critical industries such as defence, construction, aerospace, energy and maritime. Recent advancements in additive manufacturing (AM) technology enable the rapid and cost-effective...

This work investigates refill friction stir spot welded joints of AA2024-T3 aluminium alloy, produced with short welding times between 3 s and 0.75 s. A novel tool geometry that incorporates a chamfer on the inner edge of the shoulder tip is investigated as a means of improving joint quality at short welding times by easing material flow during the...

Refill friction stir spot welding is a solid-state spot-welding technique suited to lap joining of thin aluminium sheets, including difficult-to-weld 2xxx series alloys that are prone to hot cracking during fusion welding processes. Long welding time is an ongoing challenge that hinders industrial adoption of the process. To address this, the prese...

Additive manufacturing (AM) offers advantages in many aspects over conventional manufacturing techniques. These include reduced lead times and material waste. A recent topic of interest is the environmental impact of manufacturing techniques. However, there is a lack of literature detailing the impact of titanium manufacturing processes. In additio...

In this study, refill friction stir spot welding (RFSSW) was used to join AlSi10Mg, produced by laser powder bed fusion (LPBF), to high-strength wrought AA7075-T6 alloy. The investigation showed the best mechanical properties and integrity of the joint are achieved with medium heat input, where the optimal balance between hook height and integrity...

There is increasing research interest in joining lightweight metals, such as aluminium to magnesium, for potential applications in the transportation sector. The friction stir welding (FSW) technique may inhibit grain coarsening and the evolution of intermetallic compounds (IMCs) that evolve when using conventional fusion welding methods to join...

This work reports on the impact of process parameters on the intermetallic compound formation and the resultant mechanical properties of aluminium grade AA5083 to copper joints created by friction stir welding. The effect of welding speed (hence cooling rate), tool rotational speed, material placement, and tool design are considered in this analysi...

A novel approach for predicting the intermetallic compound (IMC) formation during friction stir welding (FSW) of AA6061 to commercially pure copper has been developed, in addition to their effect on mechanical properties. The temperature distribution of the aluminium to copper weld nugget determined by a finite element model, the use of an Al–Cu ph...

The main objective of this study was to assess the influence of salt concentration on the corrosion behaviour, including the role of hydrodynamic conditions, of two broad classes of ferrous engineering materials. These are comprised of alloys, typified by a low-alloy steel (UNS G43400) that corrodes actively in aqueous conditions and a range of pas...

The present study investigates the tribological properties of G350 grey cast iron in various conditions. Quench and temper heat treatments were conducted at four tempering temperatures, from 400 °C to 700 °C, to produce a range of tempered martensitic disc samples. Pins were slow furnace-cool annealed to produce a coarse pearlitic microstructure w...

The present study investigates the sliding wear properties of G350 grey cast iron following various spheroidizing annealing durations. The annealed samples were used as pins in sliding wear tests against AISI 4330 discs. Most testing combinations resulted in mild wear with little matrix damage to the cast iron pin or AISI 4330 disc. A transition to...

Environmental conditions, testing variables, and material properties significantly influence the sliding wear behaviour of all tribosystems. Such parameters affect the mechanism of wear occurring, govern how the wear scar will be categorised, and control whether transitions occur throughout the test. The present study investigated this through slid...

This study utilises a recently developed, enhanced approach to assess detailed aspects of the corrosive wear behaviour of different steel grades in aqueous slurries containing three NaCl concentrations (0.05%NaCl, 3.5%NaCl and 10%NaCl). Erosion-corrosion testing was conducted using a slurry impingement test rig and damage was quantified using volum...

In some industrial situations, components are subject to repetitive impact in the presence of a slurry. A novel repetitive impact-with-slurry test rig was developed to evaluate the behaviour of a wide range of engineering materials in such conditions. The test materials could be categorised into five main groups-heat treated steels, stainless steel...

Erosion-corrosion can be a significant issue for engineering components used in the geothermal industry. This study assesses the erosion-corrosion behaviour of a wide range of engineering alloys which are used in various parts of geothermal power plants. The evaluated materials comprised a carbon steel, low-alloy steel, three grades of stainless st...

Chromium cast irons (CCI) comprise versatile materials that encompass a range of compositions and microstructures often chosen to promote good wear resistance. There are, however, issues that arise when the cast iron is required to operate in conditions where corrosion, as well as, wear is a factor. This scenario usually results in adapting the com...

Isogrid is a highly efficient stiffened plate structure which was developed in the aerospace industry for use in rocketry and space structures. Its current form is unviable outwith these applications, as the available production methods are expensive due to excessive machining time in addition to considerable material wastage. The method detailed i...

In mining industry, various parts of pumps such as liners and impellers are deteriorated severely due to erosion-corrosion mechanisms reducing the productivity of mining process and the transportation of extracted ores. It has been found that some mines consist of chlorides, very low pH and abrasive erodent particles which enhance the materials deg...

Welding of copper and aluminium has been problematic with tradition fusion method. The friction stir welding (FSW) was employed to butt weld the T2 copper and 1061 aluminium alloy plates. The welding parameters were planned by the orthogonal experiment design method. The samples obtained in experiments were investigated in the aspects of microstruc...

The effect of salinity is assessed on the corrosive wear behaviour of a low-alloy steel (UNS G43400) and three stainless steels (UNS S15500, UNS S31600 and UNS S32760). Erosion-corrosion testing was conducted using a submerged impingement slurry jet test-rig. Three salinities were evaluated; 0.05%NaCl, 3.5%NaCl and 10%NaCl. Total volume losses (TVL...

This work aims to study the influence of the tool rotational speed and tool traverse speed on dissimilar friction stir butt welds on 3 mm thick AA5083 to commercially pure copper plates. Complex microstructures were formed in the thermo-mechanically affected zone, in which a vortex-like pattern and lamellar structures were found. Several intermetal...

Cathodic protection prolongs the service life of fluid transport and offshore engineering components by suppressing corrosion. This study assesses the effect of two cathodic protection methods, such as impressed current cathodic protection (ICCP) and sacrificial anode cathodic protection (SACP), on three ferrous-based materials under laboratory-con...

In this work, friction surfacing (FS) of AA5083 on a DH36 steel substrate was experimentally studied. The process parameters such as rotation speed, travel speed and feed rate are of great significance to the success of the FS process. Seven friction surfaced plates with different combinations of parameters were examined. Optical microscopy, SEM an...

Significant progress has been made on the implementation of friction stir welding (FSW) in the industry for aluminium alloys. However, steel FSW and other high-temperature alloys is still the subject of considerable research, mainly because of the short life and high cost of the FSW tool. Different auxiliary energies have been considered as a means...

Corrosive wear is a form of material degradation that is known to occur on equipment and components that handle suspended solids in aqueous solutions. This surface deterioration process is generally enhanced when the fluids contain chlorides that are acidic in nature. Such environments are encountered in many applications, one such example being th...

Enhancing the heat transfer to the material being welded, instead of the tool, will improve the welding thermal efficiency. Friction stir welding of 5 mm thick 6061-T6 aluminium alloy plates was carried out with the newly produced tools. It was found that the thermal efficiency increased by 4.2% using a tool with all the new design features (i.e. h...

The development of advanced joining processes such as friction stir welding (FSW) is necessary to maintain manufacturing competitiveness in any industrial nation. Substantial research that has been carried out on FSW of aluminium alloys has demonstrated considerable benefits; this has led to greater interest in FSW of steel and other high melting t...

This study compares Hot Wire Tungsten Inert Gas Stellite 6 weld cladding on a low carbon steel substrate with a lost wax cast Stellite 6 in impingement erosion-corrosion conditions. Austenitic stainless steel samples were used as a reference material. Tests were conducted in a closed loop impinged slurry vessel with a jet velocity of 18 m/s with 3....

This study investigates the corrosive wear behaviour of single and double layer Stellite 6 (UNS R30006) weld claddings and the effectiveness of nitriding on their erosion-corrosion resistance. Tests were conducted by utilising an impinging slurry jet. The slurry consisted of 3.5% NaCl aqueous solution which contained 500 µm spherical silica sand wi...

The present study reports on the erosion properties of a novel surface engineering process combining cold spray and friction stir processing. Tungsten carbide (WC-CoCr) and aluminium oxide (Al2O3) powders were cold spray co-deposited with AISI316 using a twin powder feed system. The deposited coatings were subsequently friction stir processed to re...

The efficiency of a machining process can be measured by evaluating the quality of the machined surface and the tool wear rate. The research reported herein is mainly focused on the effect of cutting parameters and tool wear on the machined surface defects, surface roughness, deformation layer and residual stresses when dry milling Stellite 6, depo...

This study forms an initial investigation into the development of SprayStir, an innovative processing technique for generating erosion resistant surface layers on a chosen substrate material. Tungsten carbide – cobalt chromium, chromium carbide – nickel chromium and aluminium oxide coatings were successfully cold spray deposited on AA5083 grade alu...

This work reports on the erosion performance of three particle reinforced metal matrix composite coatings, co-deposited with an aluminium binder via cold-gas dynamic spraying. The deposition of ceramic particles is difficult to achieve with typical cold spray techniques due to the absence of particle deformation. This issue has been overcome in the...

Understanding the residual stress state in brazed joints is crucial for the operational design and lifetime performance of the part in service. High-magnitude residual stresses are expected in the joined materials following cooling from brazing temperatures (≈950 °C) due to large mismatches in the thermal and mechanical properties. This paper aims...

This study has comprised an investigation the corrosive wear behaviour of UNS S31600, a low hardness (280Hv) UNS S42000, a high hardness (480Hv) UNS S42000 and a single layer Stellite 6 (UNS R30006) weld cladding on a low alloy carbon steel (UNS G43400). Erosion-corrosion testing was conducted using a submerged jet of 3.5% NaCl aqueous solution wit...

Friction stir welding presents many advantages over conventional welding techniques; however, there is limited published data with regard to the fatigue and bending performance of friction stir welded steels. Hence, this investigation aims to evaluate friction stir welded DH36 steel subjected to these loading conditions. A comprehensive fatigue and...

The present work reports on the examination of three High Velocity Oxy Fuel deposited coatings, Tungsten Carbide, Chromium Carbide and Aluminium Oxide, under slurry erosion and dry erosion conditions. The density and hardness of coatings produced in this manner are typically superior to other thermal spray processes, and are therefore suitable for...

The present study examines three High Velocity Oxy Fuel deposited coatings, Tungsten Carbide, Chromium Carbide and Aluminium Oxide, under slurry erosion-corrosion conditions. Coatings produced in this manner typically exhibit superior density and hardness over alternative thermal spray technologies, therefore are suitable for use in corrosive and h...

Erosion-corrosion is one of the most challenging material degradation processes that occur in engineering components that handle slurries. Materials that can withstand a combination of corrosive fluid with suspended particles are required to extend the service life of hydraulic equipment. High chromium cast irons are favorable for these application...

Engineering components, such as those which are employed in fluid sealing systems, experience abrasive wear deterioration, which is often significantly enhanced by corrosion processes and the interaction of corrosion with the mechanical damage. Broader understanding and quantification of the corrosive abrasion is appropriate to combat this complex...

Fillet welds are one of the most commonly used weld joints but one of the most difficult to weld consistently. This paper presents a technique using Artificial Neural Networks (ANN) to identify the key Gas Metal Arc Welding (GMAW) fillet weld parameters and interactions that impact on the resultant geometry, when using a metal cored wire. The input...

An extensive study on the fatigue performance of friction stir welded DH36 steel was carried out. The main focus of this experimental testing programme was fatigue testing accompanied by tensile tests, geometry measurements, hardness and residual stress measurements, and fracture surface examination. The S–N curve for friction stir butt welded join...

Friction stir welding of steel is in the early stages of development. The aim to commercialise this process creates a trade-off between welding time, cost and quality of the joint produced. Therefore, it becomes critical to analyse the lower quality bound of steel friction stir welds in conventional square edge butt welding configuration. Work has...

The alternating shielding gas technique is a method of achieving transient arc characteristics during arc welding; however the complex flow that occurs through its use has not been investigated previously. A schlieren system was used to image density gradients that arise when alternating argon and helium shield gases, under varying flow parameters,...

Erosion-corrosion is a form of material degradation that occurs in components that handle slurries in a wide range of engineering equipment. Whilst many erosion-corrosion situations (e.g. marine) involve fluids of around neutral pH, the environment is acidic in other circumstances. This paper describes the first phase of an investigation of erosion...

Friction stir welding of steel presents an array of advantages across many industrial sectors compared to conventional fusion welding techniques. Preliminary studies have identified many positive effects on the properties of welded steel components. However, the fundamental knowledge of the process in relation to structural steel remains relatively...

The corrosive wear behavior of three gas nitriding treatments (72h, 90h and 120h) on nitrided steel (BS 970-905M39) was investigated under erosion-corrosion conditions at two angles of submerged jet impingement i.e. 90o and 20o. The test solution was 3.5% NaCl. Experiments were conducted with and without the presence of a burden of suspended silica...

A comprehensive fatigue performance assessment of friction stir welded DH36 steel has been undertaken to address the relevant knowledge gap for this process on low alloy steel. A detailed set of experimental procedures specific to friction stir welding has been put forward, and the consequent study extensively examined the weld microstructure and h...

In the present study, 6 mm nominal thickness dissimilar steel plates were joined using friction stir welding. The materials used were duplex stainless steel and low alloy structural steel. The weld was assessed by metallographic examination and mechanical testing (transverse tensile and fatigue). Microstructural examination identified four distinct...

Current proposals for the divertor component of a thermonuclear fusion reactor include tungsten and copper as potentially suitable materials. This paper presents the procedures developed for the successful brazing of tungsten to oxygen free high conductivity (OFHC) copper using a fusion appropriate gold based brazing alloy, Orobraze 890 (Au80Cu20)....

This study compared the mechanical and microstructural properties produced during friction stir welding of S275 structural steel in air and underwater. Post-weld tests assessed the tensile strength, microhardness, distortion, Charpy impact toughness and fatigue performance in each case. The study showed that there was no significant difference in t...

Understanding the residual stress state in brazed joints is crucial for operational design and life time performance of the part in service. High magnitude residual stresses are expected in the joined materials following cooling from brazing temperatures (≈950C) due to large mismatches in material properties such as coefficient of thermal expansion...

In friction stir welding, assemblies are joined by means of plasticising, shearing and stirring non-molten material. The heat generation is directly related to the viscous behaviour of plasticised material, through coupled Navier-Stokes thermo-fluid flow stress equations. A significant amount of research has been conducted on aluminium friction sti...

This study considered the effect of shielding gas parameters (composition, supply method and flow rate) on the post-weld thermal properties (thermal expansion, specific heat capacity, thermal diffusivity and thermal conductivity) of the weld metal in gas metal arc welding. This is of importance as the thermal properties influence the temperature di...

A fatigue performance assessment of 6 mm thick friction stir welded DH36 steel has been undertaken, filling a significant knowledge gap in the process for steel. A comprehensive set of experimental procedures has been proposed; the consequent study extensively examined the weld microstructure, hardness, geometry and misalignments of the samples in...

A fatigue performance assessment of 6 mm thick friction stir welded DH36 steel has been undertaken, filling a significant knowledge gap in the process for steel. A comprehensive set of experimental procedures has been proposed; the consequent study extensively examined the weld mierostructure, hardness, geometry and misalignments of the samples in...

Friction Stir Processing (FSP) has been shown to improve the strength, ductility and toughness of both aluminium and steel materials through grain refinement and the even distribution of precipitates within the substrate matrix. This article presents the application of FSP of Cold Spray deposited Tungsten Carbide - Cobalt (WC-Co) of two distinct ty...

This paper presents a study on the effects of thermal autofrettage on the residual stresses in a Titanium-Copper brazed joint. It is shown that cryogenic thermal autofrettage has the potential to alter the residual stress field due to joining, in a manner that should result in an improvement in the subsequent operational fatigue performance of diss...

Friction stir welding of steel has gone through recent tool and optimisation developments allowing the process to be considered as a technically superior alternative to fusion welding. This study expanded the scientific foundation of friction stir welding of DH36 steel to analyse the effect on weld quality when the rotating tool increasingly deviat...

A fatigue performance assessment of 6 mm thick friction stir welded DH36 steel has been undertaken, filling a significant knowledge gap in the process for steel. A comprehensive set of experimental procedures has been proposed; the consequent study extensively examined the weld microstructure, hardness, geometry and misalignments of the samples in...

Friction Stir Processing (FSP) has been shown to improve the strength, ductility and toughness of both aluminium and steel materials through grain refinement and the even distribution of precipitates within the substrate matrix. This article presents the application of FSP of Cold Spray deposited Tungsten Carbide — Cobalt (WC-Co) of two distinct ty...

This study is an investigation of the effect of impingement angle on slurry erosion-corrosion of Stellite 6 manufactured by sand casting, lost wax casting and SS316. The tests were performed using an impingement rig in which a slurry with 3.5% NaCl and 1.177 g/l suspended angular sand particles at 19 m/s were recirculated for 1 h. The results were...

Stationary shoulder friction stir welding is a newly developed technique currently used for joining plates of relatively soft metals at different angular planes. The process is not currently applicable to steel, hence the present study was developed to investigate the theoretical and technical viability of stationary shoulder technology in DH36 ste...

Friction stir welding is a solid state thermomechanical deformation process from which the plasticisation behaviour of the stirred material can be evaluated through the study of flow stress evolution. Flow stress data also supporting the development of a local microstructural numerical model have been generated. Hot compression testing of DH36 stee...

In the developing DEMO divertor, the design of joints between tungsten to other fusion related materials is a significant challenge as a result of the dissimilar physical metallurgy of the materials to be joined. This paper focuses on the design and fabrication of dissimilar brazed joints between tungsten and fusion relevant materials such as EUROF...

Friction stir welding of steel presents an array of advantages across many industrial sectors compared to conventional fusion welding techniques. However, the fundamental knowledge of the friction stir welding process in relation to steel remains relatively limited. A microstructure and property evaluation of friction stir welded low alloy steel gr...

Gas tungsten arc welding requires a gas shield to be present in order to protect the arc area from contamination by atmospheric gases. As a result of each gas having its own unique thermophysical properties, the shielding gas selected can have a major influence on the arc stability, welding speed, weld appearance and geometry, mechanical properties...

This study compared the mechanical and microstructural properties produced during friction stir welding (FSW) of S275 structural steel in air and underwater. Post weld tests assessed the tensile strength, micro-hardness, distortion, Charpy impact toughness and fatigue performance in each case. The study showed that there was no significant differen...

Weld cladding was investigated using a nickel alloy clad on a high strength low alloy carbon steel substrate. The effects of pre-heat temperature, clad material and post-weld heat-treatment are examined, along with the potential for thinner clad layers using laser cladding. Experimental residual stress measurements show good correlation with the si...

Microstructural evolution of Inconel 625 and Inconel 686CPT filler metals, used for the fusion welding of clad carbon steel linepipe, has been investigated and compared. The effects of iron dilution from the linepipe parent material on the elemental segregation potential of the filler metal chemistry have been considered. The results obtained provi...

Friction stir welding of steel presents an array of advantages across many industrial sectors such as shipbuilding when compared to conventional fusion welding techniques. However, there seems to be very limited techno-economic assessment studies on its potential introduction in industry, and particularly in shipbuilding. A microstructure and prope...

For any welded component, the weld geometry is a determinative criterion that has a strong influence on the mechanical integrity of the joint. It is therefore important that the weld geometry is adequately considered when establishing the design of the component being welded. Based on the tandem submerged arc welding process, this study reports on...

This study implemented an iterative experimental approach in order to determine the shielding gas flow required to produce high-quality welds in the gas metal arc welding process with alternating shielding gases when subjected to varying velocities of cross drafts, thus determining the transitional zone where the weld quality deteriorates as a func...

Friction stir welding (FSW) of steel is an advanced joining process which is expected to deliver considerable technical and commercial benefits to the European waterborne manufacturing sector. A microstructure and property evaluation of friction stir welded DH36 6mm plate has been undertaken. The study examined a wide range of process parameters an...

A shield gas flowrate of 15–20 L min-1 is typically specified in metal inert gas welding, but is often adjusted to as high as 36 L min21 by welders in practice. Not only is this overuse of shield gas wasteful, but uncontrolled high gas flows can lead to significant turbulence induced porosity in the final weld. There is therefore a need to understa...

The transient variation of the shielding gas present in the alternating shielding gas process produces a dynamic action within the liquid weld metal. Flow vectors opposite in direction have been reported due to the various forces acting on the weld metal when argon and helium are present; however, no data have been provided to substantiate this cla...

As part of an ongoing process to fully evaluate the effects of an alternating shielding gas supply on gas shielded welding processes, a comparison between the arc pressures generated using argon, helium, alternating shielding gases and pulsed gas tungsten arc welding (GTAW) has been conducted. Arc pressure variation and peaking are two of the funda...

Three geometry changes to the inner bore of a welding nozzle and their effects on weld quality during gas metal arc welding (GMAW) were investigated through the use of computational fluid dynamic (CFD) models and experimental trials. It was shown that an increased shielding gas exit velocity increased the gas column's stability, and therefore its r...

An experimental investigation has been carried out to determine the applicability of an induction heating process with a travelling induction coil for the rectification of angular welding distortion. The results obtained from experimentation have been used to create artificial neural network (ANN) models with the ability to predict the weld-induced...

The nature and distribution of residual stresses are invariably critical for fatigue life with dis- similar material joints often inducing high tensile residual stresses. A fatigue-resistant concept of weld clad- ding process pipelines, producing compressive residual stresses, is under investigation to examine how these stresses may be influenced....

As part of an ongoing process to fully evaluate the effects of an alternating shielding gas supply on the gas tungsten arc and gas metal arc welding processes, a comparison between arc pressures produced using argon, helium, alternating gases and GTAW-P has been conducted. The alternating shielding gas process is reported to create a dynamic stirri...

With an ongoing demand to improve the efficiency of the gas metal arc welding process, steps are being taken to reduce the shielding gas consumption. However, sufficient shielding gas coverage of the weld region is essential for the generation of high quality welds, and drafts can be detrimental to its efficiency. In industry, the general practise...

A series of 4, 6 and 8 mm DH36 steel welds were produced using optimum conditions for friction stir welding (FSW). Comparator welds in the same thickness from the same plates were produced using a single sided single pass process submerged arc welds (SAW). This work was carried out to evaluate the mechanical properties of FSW material with a view t...