I t is with deep sadness that we share the news that our dear friend and colleague, Professor Geo... more I t is with deep sadness that we share the news that our dear friend and colleague, Professor George Edward Thompson, passed away after a long illness on the December 9, 2020. George was a towering presence in the light metal corrosion and protection field over his long career almost entirely based at UMIST and then at the University of Manchester. His exceptional talents were widely recognized throughout the worldwide corrosion community. His tireless commitment over more than 40 years was key to the success of the UMIST Corrosion and Protection Centre, and underpinned its reputation for excellence, both in the United Kingdom and internationally. The major financial support he gained from the U.K. research councils, the European Union, and industry was critical to its longevity. Of all his achievements, perhaps his greatest, was the opportunity he gave to the many MSc and Ph.D. students and postdoctoral workers, to study with him at the Centre, and afterwards to establish themselves in careers in academia, industry, and elsewhere. He was generous with his time and support. There are many cherished memories that will remain forever in the hearts of everyone he worked with and these are reflected in the many deeply moving messages of condolence received by his family.
Industrial interest in wrought heat-treatable aluminium-lithium (Al–Li) based alloys dates back t... more Industrial interest in wrought heat-treatable aluminium-lithium (Al–Li) based alloys dates back to around 1919 in Germany. However the exploitation of these alloys has historically been limited by their mechanical property anisotropy and concerns over their localized corrosion resistance and temperature stability. Recently, in the last ten years, alloy and process development has resulted in alloy compositions and thermomechanical treatments that potentially can overcome these issues. To put these developments in perspective we have reviewed the corrosion characteristics of first, second and third generation alloys with an emphasis on localized corrosion (intergranular and exfoliation) and stress corrosion cracking (SCC). Intergranular corrosion susceptibility of Al–Li–Cu and Al–Li–Cu–Mg alloys increases with copper content, and the depth of attack increases with ageing, i.e. UA PA<OA. SCC initiation from smooth surfaces is rare for copper-free Al–Li alloys irrespective of temper or whether exposure is under continuous or alternate immersion conditions. For copper-containing alloys, initiation remains difficult for smooth specimens under continuous immersion conditions, but occurs readily under conditions of alternate immersion. It is likely that crack initiation is controlled by an anodic dissolution dominated process, but crack propagation may be controlled by either anodic dissolution or a hydrogen related process. Test results reviewed to date on thin plate samples show that the lower lithium content third generation Al–Li alloys, with suitable zinc and/or silver additions and thermomechanical processing can provide an acceptable resistance to localized corrosion (IGC and Exfoliation) and SCC in near to peak aged tempers. For this conclusion to apply to thicker products (>~30 mm) further analysis of corrosion test results is required.
It has been found that a high purity AI-6.%Zn-3 ~oMg becomes embrittled if pre-exposed to moist g... more It has been found that a high purity AI-6.%Zn-3 ~oMg becomes embrittled if pre-exposed to moist gases prior to tensile testing. The degree of embrittlement increases with the time of preexposure and with the temperature and relative humidity of the pre-exposure environment. The alloy is most sensitive to embrittlement when solution treated at 475°C but this sensitivity can be reduced considerably if the surface film formed at 475°C is removed by electropolishing. The embrittlement is not strain-rate sensitive and the ductility of the pre-exposed alloy cannot be recovered by storing unstressed in dry air or in vacuo. However, the ductility of embrittled specimens can be fully restored if tensile testing is carried out under vacuum. If 1.7.%o copper or 0.14~ chromium are added to the high purity alloy the rate of embrittlement is reduced and is even more reduced in the commercial 7075 alloy. Also, both the chromium containing alloy and the commercial alloy recover their ductilities during storage in laboratory aii" at room temperature-the rate of recovery being much higher than the rate of embrittlement. It is proposed that embrittlement is due to the deep penetration of an agent such as atomic hydrogen which reduces the grain boundary cohesion. It is also proposed that a similar effect must occur during the intergranular stress corrosion failure of AI-Zn-Mg alloys.
High voltage electron metallographic studies of stress corrosion cracks nucleated on miniature U-... more High voltage electron metallographic studies of stress corrosion cracks nucleated on miniature U-bend specimens of austenitic stainless steels support an anodie dissolution mechanism of cracking. For all the alloys examined crack nucleation occurs at slip traces and a characteristic slotted dissolution morphology is observed in crack tip regions. The crystallography of this attack as determined by stereo-microscopy and trace analysis, reveals the slots to be bounded by {110) planes whilst growing in < 111 > directions. Cracking occurs through the network of corrosion slots at the crack tip and the well known features of stress corrosion fracture surfaces can be interpreted by this mechanism.
Intensive melt shearing was achieved using a twin-screw machine to condition an aluminium alloy p... more Intensive melt shearing was achieved using a twin-screw machine to condition an aluminium alloy prior to solidification. The results show that intensive melt shearing has a significant grain-refining effect. In addition, the intensive melt shearing reduces both the volume fraction and the size of porosity. It can reduce the density index from 10.50% to 2.87% and the average size of porosity in the samples solidified under partial vacuum from around 1 mm to 100 μm.
International Journal of Cast Metals Research, 2009
Intensive shearing was applied to alloy melts at temperatures above their liquidus by using a twi... more Intensive shearing was applied to alloy melts at temperatures above their liquidus by using a twinscrew mechanism. The sheared melt was then cast into a TP1 mould for microstructural examination. Alloy melts with or without shearing were also filtered using the Prefil technique developed by N-Tech Ltd in order to analyse oxides and other second phase particles. The experimental results showed a significant grain refinement through enhancement of heterogeneous nucleation. The intensive melt shearing converted oxide films and agglomerates into well dispersed fine particles with a narrow size distribution. It was confirmed that the fine oxide particles can act as potent sites for nucleation during the solidification of the sheared melt. This paper presents the experimental results and theoretical analysis of shear enhanced heterogeneous nucleation during solidification of Mg-and Al-alloys. A multi-step heterogeneous nucleation mechanism has been proposed and discussed.
The brief expression of corrosion of aluminum and its alloys was given in this review with partic... more The brief expression of corrosion of aluminum and its alloys was given in this review with particular emphasis on the pertinent application of those materials to various environments. The corrosion characteristics of alloys and the methods of corrosion controle were also presented.
The thermomechanical processing involved in aluminium sheet production induces significant micros... more The thermomechanical processing involved in aluminium sheet production induces significant microstructural changes to the outermost surface layers of the metal substrate relative to the bulk material. The microstructural state of this modified surface layer has been shown to play a determining role in the final corrosion and electrochemical properties of the sheet. The current work explores the role of surface grinding and subsequent thermal treatment on the microstructural and corrosion properties of the near-surface region of alloy AA3005 commonly used for architectural applications. The study includes detailed microstructural and corrosion resistance characterisation combining ultramicrotomy / TEM, glow discharge optical emission spectroscopy (GD-OES) and high resolution FEG-SEM with filiform corrosion testing. The results show a clear correlation between the amount of surface deformation induced by various grinding practices, the resulting near-surface microstructure and the cor...
My background is more than 30 years of industrial experience working in R&D in the aluminium indu... more My background is more than 30 years of industrial experience working in R&D in the aluminium industry from a UK base mainly for Alcan and for the past four years for Innoval Technology. My role during most of that time has been to identify and bring new technology into the aluminium industry, with the emphasis on step change or socalled disruptive technology. To use an analogy: my work has all been about laying new track, rather than following the railroad.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Scanning Kelvin Probe (SKP) potentiometry is used to systematically investigate the effect of sur... more Scanning Kelvin Probe (SKP) potentiometry is used to systematically investigate the effect of surface abrasion and subsequent heat-treatment on the open-circuit potential in humid air of the AA6016 surface. SKP is also used to follow the kinetics of filiform corrosion and to determine characteristic potentials associated with the electrolyte-filled filiform head and dry filiform tail. It is shown that simply abrading with 180 grit SiC produces a surface potential up to 0.5V lower than the bulk. When the abraded sample is overcoated with a 30 micron layer of PVB (polyvinyl butyral) and exposed to HCl a fast, superficial filiform corrosion (FFC) is observed in which metal loss is limited to the thickness of the surface layer. Filiform head OCP values are similar to that of the surface layer, whereas filiform tail OCP values are similar to the bulk. A mechanism is proposed in which the ultra-fine grain structure of the surface layer produces an anodic activation and the potential diffe...
The filiform corrosion behaviour of hot-rolled AA3104 aluminium alloy was investigated in the pre... more The filiform corrosion behaviour of hot-rolled AA3104 aluminium alloy was investigated in the presence of a near-surface deformed layer produced by hot rolling. Through detailed examination of microstructure of the near-surface deformed layer and observation of the propagation behaviour of filiform corrosion, it was found that lateral development of surface-active filiform corrosion in the deformed layer was promoted by magnesium oxide in bands and manganese-containing dispersoids. Further, successive-pitting filiform corrosion was observed along the underlying grain boundaries of the bulk alloy, which develops into crystallographic corrosion of the grain interiors.
ABSTRACT The performance and characteristics of a no rinse, titanium based conversion coating on ... more ABSTRACT The performance and characteristics of a no rinse, titanium based conversion coating on an aluminium alloy have been studied using electrochemical techniques and transmission electron microscopy. Coatings were prepared from an aqueous H2 TiF6 solution, spin coated onto aluminium alloy 3003. The electrochemical behaviour evolves with time during exposure to 0·5% and 3·5%NaCl. Polarisation curves and impedance data correspond well and indicate that the anodic inhibition and polarisation resistance increase dramatically with time. However, no cathodic inhibition is found. Metastable pitting was observed at potentials below the pitting potential. TEM micrographs taken from cross-sections of coated material show that the coating thickness is of the order of 30 nm and that with immersion a mixed metal oxide layer appears at the substrate/coating interface.
ABSTRACT A nano-structured, near-surface layer has been generated by mechanically grinding an AA6... more ABSTRACT A nano-structured, near-surface layer has been generated by mechanically grinding an AA6111 alloy. After heat treatment at 180°C for 30 minutes, Q phase particles, ~20 nm diameter, were precipitated preferentially at grain boundaries within the nano-structured nearsurface layer. No such precipitates were observed in the bulk alloy after this heat treatment. This preferential precipitation results in the near-surface layers having increased corrosion susceptibility than the bulk microstructure, due to the micro-galvanic coupling between the precipitates at grain boundary and the grain matrix. The localized attack is predominately intergranular.
I t is with deep sadness that we share the news that our dear friend and colleague, Professor Geo... more I t is with deep sadness that we share the news that our dear friend and colleague, Professor George Edward Thompson, passed away after a long illness on the December 9, 2020. George was a towering presence in the light metal corrosion and protection field over his long career almost entirely based at UMIST and then at the University of Manchester. His exceptional talents were widely recognized throughout the worldwide corrosion community. His tireless commitment over more than 40 years was key to the success of the UMIST Corrosion and Protection Centre, and underpinned its reputation for excellence, both in the United Kingdom and internationally. The major financial support he gained from the U.K. research councils, the European Union, and industry was critical to its longevity. Of all his achievements, perhaps his greatest, was the opportunity he gave to the many MSc and Ph.D. students and postdoctoral workers, to study with him at the Centre, and afterwards to establish themselves in careers in academia, industry, and elsewhere. He was generous with his time and support. There are many cherished memories that will remain forever in the hearts of everyone he worked with and these are reflected in the many deeply moving messages of condolence received by his family.
Industrial interest in wrought heat-treatable aluminium-lithium (Al–Li) based alloys dates back t... more Industrial interest in wrought heat-treatable aluminium-lithium (Al–Li) based alloys dates back to around 1919 in Germany. However the exploitation of these alloys has historically been limited by their mechanical property anisotropy and concerns over their localized corrosion resistance and temperature stability. Recently, in the last ten years, alloy and process development has resulted in alloy compositions and thermomechanical treatments that potentially can overcome these issues. To put these developments in perspective we have reviewed the corrosion characteristics of first, second and third generation alloys with an emphasis on localized corrosion (intergranular and exfoliation) and stress corrosion cracking (SCC). Intergranular corrosion susceptibility of Al–Li–Cu and Al–Li–Cu–Mg alloys increases with copper content, and the depth of attack increases with ageing, i.e. UA PA<OA. SCC initiation from smooth surfaces is rare for copper-free Al–Li alloys irrespective of temper or whether exposure is under continuous or alternate immersion conditions. For copper-containing alloys, initiation remains difficult for smooth specimens under continuous immersion conditions, but occurs readily under conditions of alternate immersion. It is likely that crack initiation is controlled by an anodic dissolution dominated process, but crack propagation may be controlled by either anodic dissolution or a hydrogen related process. Test results reviewed to date on thin plate samples show that the lower lithium content third generation Al–Li alloys, with suitable zinc and/or silver additions and thermomechanical processing can provide an acceptable resistance to localized corrosion (IGC and Exfoliation) and SCC in near to peak aged tempers. For this conclusion to apply to thicker products (>~30 mm) further analysis of corrosion test results is required.
It has been found that a high purity AI-6.%Zn-3 ~oMg becomes embrittled if pre-exposed to moist g... more It has been found that a high purity AI-6.%Zn-3 ~oMg becomes embrittled if pre-exposed to moist gases prior to tensile testing. The degree of embrittlement increases with the time of preexposure and with the temperature and relative humidity of the pre-exposure environment. The alloy is most sensitive to embrittlement when solution treated at 475°C but this sensitivity can be reduced considerably if the surface film formed at 475°C is removed by electropolishing. The embrittlement is not strain-rate sensitive and the ductility of the pre-exposed alloy cannot be recovered by storing unstressed in dry air or in vacuo. However, the ductility of embrittled specimens can be fully restored if tensile testing is carried out under vacuum. If 1.7.%o copper or 0.14~ chromium are added to the high purity alloy the rate of embrittlement is reduced and is even more reduced in the commercial 7075 alloy. Also, both the chromium containing alloy and the commercial alloy recover their ductilities during storage in laboratory aii" at room temperature-the rate of recovery being much higher than the rate of embrittlement. It is proposed that embrittlement is due to the deep penetration of an agent such as atomic hydrogen which reduces the grain boundary cohesion. It is also proposed that a similar effect must occur during the intergranular stress corrosion failure of AI-Zn-Mg alloys.
High voltage electron metallographic studies of stress corrosion cracks nucleated on miniature U-... more High voltage electron metallographic studies of stress corrosion cracks nucleated on miniature U-bend specimens of austenitic stainless steels support an anodie dissolution mechanism of cracking. For all the alloys examined crack nucleation occurs at slip traces and a characteristic slotted dissolution morphology is observed in crack tip regions. The crystallography of this attack as determined by stereo-microscopy and trace analysis, reveals the slots to be bounded by {110) planes whilst growing in < 111 > directions. Cracking occurs through the network of corrosion slots at the crack tip and the well known features of stress corrosion fracture surfaces can be interpreted by this mechanism.
Intensive melt shearing was achieved using a twin-screw machine to condition an aluminium alloy p... more Intensive melt shearing was achieved using a twin-screw machine to condition an aluminium alloy prior to solidification. The results show that intensive melt shearing has a significant grain-refining effect. In addition, the intensive melt shearing reduces both the volume fraction and the size of porosity. It can reduce the density index from 10.50% to 2.87% and the average size of porosity in the samples solidified under partial vacuum from around 1 mm to 100 μm.
International Journal of Cast Metals Research, 2009
Intensive shearing was applied to alloy melts at temperatures above their liquidus by using a twi... more Intensive shearing was applied to alloy melts at temperatures above their liquidus by using a twinscrew mechanism. The sheared melt was then cast into a TP1 mould for microstructural examination. Alloy melts with or without shearing were also filtered using the Prefil technique developed by N-Tech Ltd in order to analyse oxides and other second phase particles. The experimental results showed a significant grain refinement through enhancement of heterogeneous nucleation. The intensive melt shearing converted oxide films and agglomerates into well dispersed fine particles with a narrow size distribution. It was confirmed that the fine oxide particles can act as potent sites for nucleation during the solidification of the sheared melt. This paper presents the experimental results and theoretical analysis of shear enhanced heterogeneous nucleation during solidification of Mg-and Al-alloys. A multi-step heterogeneous nucleation mechanism has been proposed and discussed.
The brief expression of corrosion of aluminum and its alloys was given in this review with partic... more The brief expression of corrosion of aluminum and its alloys was given in this review with particular emphasis on the pertinent application of those materials to various environments. The corrosion characteristics of alloys and the methods of corrosion controle were also presented.
The thermomechanical processing involved in aluminium sheet production induces significant micros... more The thermomechanical processing involved in aluminium sheet production induces significant microstructural changes to the outermost surface layers of the metal substrate relative to the bulk material. The microstructural state of this modified surface layer has been shown to play a determining role in the final corrosion and electrochemical properties of the sheet. The current work explores the role of surface grinding and subsequent thermal treatment on the microstructural and corrosion properties of the near-surface region of alloy AA3005 commonly used for architectural applications. The study includes detailed microstructural and corrosion resistance characterisation combining ultramicrotomy / TEM, glow discharge optical emission spectroscopy (GD-OES) and high resolution FEG-SEM with filiform corrosion testing. The results show a clear correlation between the amount of surface deformation induced by various grinding practices, the resulting near-surface microstructure and the cor...
My background is more than 30 years of industrial experience working in R&D in the aluminium indu... more My background is more than 30 years of industrial experience working in R&D in the aluminium industry from a UK base mainly for Alcan and for the past four years for Innoval Technology. My role during most of that time has been to identify and bring new technology into the aluminium industry, with the emphasis on step change or socalled disruptive technology. To use an analogy: my work has all been about laying new track, rather than following the railroad.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Scanning Kelvin Probe (SKP) potentiometry is used to systematically investigate the effect of sur... more Scanning Kelvin Probe (SKP) potentiometry is used to systematically investigate the effect of surface abrasion and subsequent heat-treatment on the open-circuit potential in humid air of the AA6016 surface. SKP is also used to follow the kinetics of filiform corrosion and to determine characteristic potentials associated with the electrolyte-filled filiform head and dry filiform tail. It is shown that simply abrading with 180 grit SiC produces a surface potential up to 0.5V lower than the bulk. When the abraded sample is overcoated with a 30 micron layer of PVB (polyvinyl butyral) and exposed to HCl a fast, superficial filiform corrosion (FFC) is observed in which metal loss is limited to the thickness of the surface layer. Filiform head OCP values are similar to that of the surface layer, whereas filiform tail OCP values are similar to the bulk. A mechanism is proposed in which the ultra-fine grain structure of the surface layer produces an anodic activation and the potential diffe...
The filiform corrosion behaviour of hot-rolled AA3104 aluminium alloy was investigated in the pre... more The filiform corrosion behaviour of hot-rolled AA3104 aluminium alloy was investigated in the presence of a near-surface deformed layer produced by hot rolling. Through detailed examination of microstructure of the near-surface deformed layer and observation of the propagation behaviour of filiform corrosion, it was found that lateral development of surface-active filiform corrosion in the deformed layer was promoted by magnesium oxide in bands and manganese-containing dispersoids. Further, successive-pitting filiform corrosion was observed along the underlying grain boundaries of the bulk alloy, which develops into crystallographic corrosion of the grain interiors.
ABSTRACT The performance and characteristics of a no rinse, titanium based conversion coating on ... more ABSTRACT The performance and characteristics of a no rinse, titanium based conversion coating on an aluminium alloy have been studied using electrochemical techniques and transmission electron microscopy. Coatings were prepared from an aqueous H2 TiF6 solution, spin coated onto aluminium alloy 3003. The electrochemical behaviour evolves with time during exposure to 0·5% and 3·5%NaCl. Polarisation curves and impedance data correspond well and indicate that the anodic inhibition and polarisation resistance increase dramatically with time. However, no cathodic inhibition is found. Metastable pitting was observed at potentials below the pitting potential. TEM micrographs taken from cross-sections of coated material show that the coating thickness is of the order of 30 nm and that with immersion a mixed metal oxide layer appears at the substrate/coating interface.
ABSTRACT A nano-structured, near-surface layer has been generated by mechanically grinding an AA6... more ABSTRACT A nano-structured, near-surface layer has been generated by mechanically grinding an AA6111 alloy. After heat treatment at 180°C for 30 minutes, Q phase particles, ~20 nm diameter, were precipitated preferentially at grain boundaries within the nano-structured nearsurface layer. No such precipitates were observed in the bulk alloy after this heat treatment. This preferential precipitation results in the near-surface layers having increased corrosion susceptibility than the bulk microstructure, due to the micro-galvanic coupling between the precipitates at grain boundary and the grain matrix. The localized attack is predominately intergranular.
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