Geoff Scamans - Academia.edu (original) (raw)

Papers by Geoff Scamans

Corrosion

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.

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...

Shear deformation during rolling leads to the formation of a highly deformed layer at the surface... more Shear deformation during rolling leads to the formation of a highly deformed layer at the surface of rolled sheet. Subsequent annealing leads to enhanced precipitation of fine intermetallic particles in the surface layers. These layers have high electrochemical reactivity, in particular, a strong susceptibility to filiform corrosion. The electrochemical behaviour and microstructure of the active deformed layer at the surface of a rolled commercial AA3005 alloy and an analogue model alloy (Al-0.4Fe-o03Si-1.0Mn) was investigated by sputtering the surface to different depths. The active layer was found to be of the order of 1 mm in thickness. The increased number of intermetallic particles in the surface was found to cause an increase in the cathodic reactivity relative to the bulk. The high number ofpit nucleation sites and matrix Mn-depletion resulting from precipitation was found to increase the pitting susceptibility of the surface. The relationship between Mn-depletion and anodic ...

Treatise on Materials Science & Technology, 1989

Aluminum-lithium Alloys, 2014

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.

Scripta Metallurgica, 1979

Scripta Metallurgica, 1985

Shreir's Corrosion, 2010

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.

Scripta Materialia, 2011

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.

New Scientist, 1986

... Corporate Authors: IPC Magazine Limited. King's Reach Tower, Stamford Street London SE1 ... more ... Corporate Authors: IPC Magazine Limited. King's Reach Tower, Stamford Street London SE1 9LS England. Availability: IPC Magazine Limited. King's Reach Tower, Stamford Street London SE1 9LS England. Find a library where document is available. ...

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.

Corrosion Science, 1978

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.

Corrosion Science, 1976

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.

Corrosion

The European Aviation Safety Agency’s recent safety information bulletin (SIB 2018-04R2) describe... more The European Aviation Safety Agency’s recent safety information bulletin (SIB 2018-04R2) describes a brittle intergranular cracking phenomenon in 7xxx aluminum alloys and recommends testing conditions. These testing conditions are severe compared with expectations regarding, temperature, humidity, and stress in aerostructures. In this study, strong increases in time to failure of smooth specimens tested in humid air were observed when reducing either temperature or stress to levels closer to what is representative of in-service conditions. The cracking morphologies after testing in hot, humid air were identical to those described in the literature for in-service occurrences of stress corrosion cracking (SCC), including the observation of crack arrest markings consistent with a mechanism of alternate local corrosion and crack propagation by hydrogen embrittlement. The differences between such fracture surfaces and those observed in the industry standard SCC screening test, which uses...

Journal of Physics: Conference Series, 2006

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.

For the manufacture of these products, Heat Trace has installed a continuous metal extrusion deve... more For the manufacture of these products, Heat Trace has installed a continuous metal extrusion development line. Aluminium can be fed in a number of forms, including rod and granules. Solid sections can be produced using the radial process, operating in the tangential mode, which enables articles to be sheathed with a patent-protected continuous coating. Although the replacement of copper conductors and stainless steel jackets with aluminium has resulted in major cost savings, the major advantage is that aluminium enabled different design geometries and concepts to be used. This work has produced a range of novel aluminium-based heating products, which have major technical benefits and include the following applications: 1) Trace heating cables used for freeze protection and temperature control (oil refineries, chemical plants) 2) Automotive heated products for underseat heating, heated fluid pipes (AdBlue, windscreen washer liquid), tank heaters and heated washer nozzles 3) Rail heat...

The effect of the metal substrate microstructure on FFC susceptibility was investigated for super... more The effect of the metal substrate microstructure on FFC susceptibility was investigated for super purity based AA 6111 model alloys. For cold rolled and laboratory simulated continuously annealed materials, the FFC susceptibility of the surface substrate was found to decrease with increasing Cu content, while the iron content, at the levels investigated, did not strongly affect FFC properties. Subsequent paint baking was found to reduce the FFC susceptibility further. Alkaline etching and desmutting before coating resulted in a significant reduction of the FFC susceptibility for all alloys and substrate conditions investigated.

Corrosion

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.

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...

Shear deformation during rolling leads to the formation of a highly deformed layer at the surface... more Shear deformation during rolling leads to the formation of a highly deformed layer at the surface of rolled sheet. Subsequent annealing leads to enhanced precipitation of fine intermetallic particles in the surface layers. These layers have high electrochemical reactivity, in particular, a strong susceptibility to filiform corrosion. The electrochemical behaviour and microstructure of the active deformed layer at the surface of a rolled commercial AA3005 alloy and an analogue model alloy (Al-0.4Fe-o03Si-1.0Mn) was investigated by sputtering the surface to different depths. The active layer was found to be of the order of 1 mm in thickness. The increased number of intermetallic particles in the surface was found to cause an increase in the cathodic reactivity relative to the bulk. The high number ofpit nucleation sites and matrix Mn-depletion resulting from precipitation was found to increase the pitting susceptibility of the surface. The relationship between Mn-depletion and anodic ...

Treatise on Materials Science & Technology, 1989

Aluminum-lithium Alloys, 2014

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.

Scripta Metallurgica, 1979

Scripta Metallurgica, 1985

Shreir's Corrosion, 2010

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.

Scripta Materialia, 2011

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.

New Scientist, 1986

... Corporate Authors: IPC Magazine Limited. King's Reach Tower, Stamford Street London SE1 ... more ... Corporate Authors: IPC Magazine Limited. King's Reach Tower, Stamford Street London SE1 9LS England. Availability: IPC Magazine Limited. King's Reach Tower, Stamford Street London SE1 9LS England. Find a library where document is available. ...

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.

Corrosion Science, 1978

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.

Corrosion Science, 1976

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.

Corrosion

The European Aviation Safety Agency’s recent safety information bulletin (SIB 2018-04R2) describe... more The European Aviation Safety Agency’s recent safety information bulletin (SIB 2018-04R2) describes a brittle intergranular cracking phenomenon in 7xxx aluminum alloys and recommends testing conditions. These testing conditions are severe compared with expectations regarding, temperature, humidity, and stress in aerostructures. In this study, strong increases in time to failure of smooth specimens tested in humid air were observed when reducing either temperature or stress to levels closer to what is representative of in-service conditions. The cracking morphologies after testing in hot, humid air were identical to those described in the literature for in-service occurrences of stress corrosion cracking (SCC), including the observation of crack arrest markings consistent with a mechanism of alternate local corrosion and crack propagation by hydrogen embrittlement. The differences between such fracture surfaces and those observed in the industry standard SCC screening test, which uses...

Journal of Physics: Conference Series, 2006

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.

For the manufacture of these products, Heat Trace has installed a continuous metal extrusion deve... more For the manufacture of these products, Heat Trace has installed a continuous metal extrusion development line. Aluminium can be fed in a number of forms, including rod and granules. Solid sections can be produced using the radial process, operating in the tangential mode, which enables articles to be sheathed with a patent-protected continuous coating. Although the replacement of copper conductors and stainless steel jackets with aluminium has resulted in major cost savings, the major advantage is that aluminium enabled different design geometries and concepts to be used. This work has produced a range of novel aluminium-based heating products, which have major technical benefits and include the following applications: 1) Trace heating cables used for freeze protection and temperature control (oil refineries, chemical plants) 2) Automotive heated products for underseat heating, heated fluid pipes (AdBlue, windscreen washer liquid), tank heaters and heated washer nozzles 3) Rail heat...

The effect of the metal substrate microstructure on FFC susceptibility was investigated for super... more The effect of the metal substrate microstructure on FFC susceptibility was investigated for super purity based AA 6111 model alloys. For cold rolled and laboratory simulated continuously annealed materials, the FFC susceptibility of the surface substrate was found to decrease with increasing Cu content, while the iron content, at the levels investigated, did not strongly affect FFC properties. Subsequent paint baking was found to reduce the FFC susceptibility further. Alkaline etching and desmutting before coating resulted in a significant reduction of the FFC susceptibility for all alloys and substrate conditions investigated.