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Marie-georges Olivier - One of the best experts on this subject based on the ideXlab platform.
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Investigation by electrochemical impedance spectroscopy of Filiform Corrosion of electrocoated steel substrates
Progress in Organic Coatings, 2015Co-Authors: Anne-pascale Romano, Marie-georges OlivierAbstract:Abstract This work aims at studying by electrochemical impedance spectroscopy (EIS) the susceptibility to Filiform Corrosion of low carbon steel covered by cataphoretic coating. The determination of the exposed metallic area variations of scratched samples during ageing test is an estimation of the disbonding of the coating and/or the Filiform Corrosion. This area can be evaluated by electrochemical impedance spectroscopy (EIS). A simplified electrical equivalent model used to estimate the exposed metallic area is valid if the Corrosion products are correctly dissolved before characterization. Furthermore the steel is a very complex substrate and thus many parameters must be optimized in order to remove the Corrosion products before EIS measurements.
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Filiform Corrosion of electrocoated aluminium alloy: Role of surface pretreatment
Corrosion Science, 2012Co-Authors: Andrej Nazarov, Dominique Thierry, Flavio Deflorian, Michele Fedel, Anne-pascale Romano, Marie-georges OlivierAbstract:Abstract Commercial Oxsilan, 3-aminopropyltriethoxysilane and sol–gel siloxane coatings were applied on AA6016 aluminium alloy before electrocoating. Standard Filiform Corrosion test demonstrated the pre-treatment role on the under-paint Corrosion rate. All pre-treatments increase the coating adhesion in water electrolyte (EIS). Anodic undermining is the mechanism of the coatings de-adhesion (SKP). Electromotive force (difference in potentials of defect-surrounding interface) and interface ability to promote the chloride migration are rate-determining factors of the Filiform Corrosion. Contrary to other pre-treatments, the aminosiloxane decreases the interfacial potential, facilitates the chlorides migration and leads to anodic de-adhesion of large coated areas (Tof-SIMS and EDXS).
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silane sol gel film as pretreatment for improvement of barrier properties and Filiform Corrosion resistance of 6016 aluminium alloy covered by cataphoretic coating
Progress in Organic Coatings, 2011Co-Authors: Anne-pascale Romano, M Fedel, F Deflorian, Marie-georges OlivierAbstract:Abstract The aim of this study is to develop a newly silane sol–gel pretreatment on the barrier properties and Filiform Corrosion resistance of 6016 aluminium alloy covered by cataphoretic coating. The sol–gel coatings are used as coupling agent between aluminium substrate and cataphoretic paint. The pretreatment is an aqueous solution of three different silane compounds (glycidyloxypropyltrimethoxysilane (GPS), tetraethoxysilane (TEOS) and methyltriethoxysilane (MTES)) hydrolysed at two different pH (2 and 3.5). A system without pretreatment was studied as reference. The electrocoatings were cured between 155 °C and 195 °C in order to modify their mechanical properties. Polarisation curves, EIS and FT-IR measurements were used in order to characterize the silane layers. EIS measurements were used to follow the barrier properties and the water uptake evolution on intact coatings. The Filiform Corrosion protection of the coating was also evaluated by a normalized Filiform Corrosion test.
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Silane sol–gel film as pretreatment for improvement of barrier properties and Filiform Corrosion resistance of 6016 aluminium alloy covered by cataphoretic coating
Progress in Organic Coatings, 2011Co-Authors: Anne-pascale Romano, Flavio Deflorian, Michele Fedel, Marie-georges OlivierAbstract:Abstract The aim of this study is to develop a newly silane sol–gel pretreatment on the barrier properties and Filiform Corrosion resistance of 6016 aluminium alloy covered by cataphoretic coating. The sol–gel coatings are used as coupling agent between aluminium substrate and cataphoretic paint. The pretreatment is an aqueous solution of three different silane compounds (glycidyloxypropyltrimethoxysilane (GPS), tetraethoxysilane (TEOS) and methyltriethoxysilane (MTES)) hydrolysed at two different pH (2 and 3.5). A system without pretreatment was studied as reference. The electrocoatings were cured between 155 °C and 195 °C in order to modify their mechanical properties. Polarisation curves, EIS and FT-IR measurements were used in order to characterize the silane layers. EIS measurements were used to follow the barrier properties and the water uptake evolution on intact coatings. The Filiform Corrosion protection of the coating was also evaluated by a normalized Filiform Corrosion test.
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influence of crosslinking density of a cataphoretic coating on initiation and propagation of Filiform Corrosion of aa6016
Progress in Organic Coatings, 2009Co-Authors: Anne-pascale Romano, Andrej Nazarov, Marie-georges Olivier, Dominique ThierryAbstract:The effect of curing temperature on initiation and propagation of Filiform Corrosion of an epoxy cataphoretic electrocoating deposited on aluminum alloy substrate was studied. EIS measurements were used to follow the evolution of the water uptake of the intact coatings. In addition, EIS was applied to determine the performances of the systems as a result of exposure to HCl vapours. Cantilever method (stressmeter) was used to determine the stresses generated in an organic coating during a humidity cycle. Scanning Kelvin Probe (SKP) was applied in order to investigate the initiation and propagation of Filiform Corrosion of painted aluminum alloy. The mechanism of Filiform Corrosion is discussed according to the paint properties.
Geraint Williams - One of the best experts on this subject based on the ideXlab platform.
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the effect of composition and thickness on the mechanism and kinetics of Filiform Corrosion occurring on zinc aluminium magnesium coated steel
Corrosion Science, 2020Co-Authors: N. Wint, Geraint Williams, D. Eaves, H. N. McmurrayAbstract:Abstract The effect of coating thickness and composition on the kinetics of acetic acid-induced Filiform Corrosion (FFC) on Zinc-Aluminium-Magnesium (ZAM) coated steel is investigated. Scribe defects are created in organic coatings applied to ∼10 µm coatings of varying composition (1-6 wt.%. Al, 1-3 wt. % Mg), and fixed composition (Zn-1.5 wt. % Al- 1.5 wt.% Mg) but varying thickness (5-27 µm). FCC decreases with increasing Al (at fixed wt. % Mg) and thickness. A linear trend exists between thickness and iron exposure time. Findings are consistent with FFC advancing via a penetrative coating mechanism whereby exposed iron couples to the coating.
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The Kinetics and Mechanism of Filiform Corrosion occurring on Zinc-Aluminium-Magnesium coated steel
Corrosion Science, 2019Co-Authors: N. Wint, Geraint Williams, Emmanouela Michailidou, D. Eaves, A. Bennett, Justin Searle, Hamilton Neil McmurrayAbstract:Abstract This paper describes a systematic study into the initiation and propagation of Filiform Corrosion (FFC) on industrially important Zinc-Aluminium-Magnesium (ZAM) alloy coatings for steels. An artificial scribe defect is created in model organic coatings applied to ZAM. Corrosion is initiated using HCl, NaCl, FeCl2 and acetic acid. Only acetic acid is able to reproducibly initiate FFC. The FFC (area) rate is shown to be proportional to the amount of acetic acid introduced. The FFC mechanism is explained in terms of the relative susceptibility of alloy phases to anodic dissolution, determined using scanning electron microscopy and scanning Kelvin probe force microscopy.
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Inhibition of Filiform Corrosion on Organic-Coated Magnesium-Containing Galvanized Steel by Smart-Release Ion Exchange Pigments
ECS Transactions, 2017Co-Authors: Emmanouela Michailidou, Hamilton Neil Mcmurray, Geraint WilliamsAbstract:This paper describes a systematic kinetic study on the inhibitory effect of anion exchange Hydrotalcite-based pigments on Filiform corroding hot dipped Zn-(1-2 w%)Mg-(1-2 w%)Al galvanized steel. Filiform Corrosion was initiated via scribing the organic-coated samples and introducing a corrosive electrolyte in the defect. Following Filiform Corrosion initiation, the time-dependent extent of coating delamination was determined photographically over a period of six weeks. It is positively demonstrated that the addition of smart-release pigments in the organic coating greatly suppresses the rate of Filiform Corrosion. The inhibitor efficiency is shown to increase in the order: carbonate < benzotriazole < benzotriazolate. The release of carbonates leads to Filiform Corrosion increase.
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Inhibition of Corrosion-driven organic coating delamination and Filiform Corrosion on iron by phenyl phosphonic acid
Progress in Organic Coatings, 2017Co-Authors: Carol Glover, Geraint WilliamsAbstract:In-coating phenyl phosphonic acid (H2PP) additions are investigated as inhibitors of Corrosion-driven organic coating disbondment and anodic Filiform Corrosion (FFC) on iron surfaces. In-situ scanning Kelvin probe (SKP) experiments under atmospheric Corrosion conditions are used to study the influence of the quantity of dissolved H2PP in the organic coating on the kinetics of cathodic delamination. It is demonstrated that, in a standard delamination investigation, increasing levels of H2PP progressively decrease the delamination rate up to 55%. In-coating H2PP additions are shown to be much more effective in a realistic scenario where electrolyte additions are made to a scribed defect and rates of cathodic disbondment are slowed by up to 99%. From the observed delamination kinetics, an inhibition mechanism is proposed whereby H2PP additions interact with the underlying iron to form an interfacial salt layer that blocks underfilm oxygen reduction. In terms of FFC inhibition, a threshold has been established whereby, with additions of 10% or below H2PP is shown to enhance the filament propagation rate due Cl− attack via an insufficient blocking layer. However, above 10% H2PP additions, propagation is slowed by up to 76%.
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The Kinetics and Mechanism of Atmospheric Corrosion Occurring on Tin and Iron-Tin Intermetallic Coated Steels II. Filiform Corrosion
Journal of The Electrochemical Society, 2015Co-Authors: N. Wint, Geraint Williams, Hamilton Neil Mcmurray, A.c.a. De VooysAbstract:This paper describes a systematic study into the initiation and propagation of Filiform Corrosion (FFC) on pure iron, pure tin and industrially important tin and iron-tin intermetallic (FeSn and FeSn2) coatings for packaging steels, as a function of coating weight. The time-dependent extent of FFC was determined optically. FFC was not observed on pure tin or tin coatings but was found to propagate at significantly reduced rates on the FeSn and FeSn2 intermetallic coatings, when compared to pure iron. An explanation of the findings is given, firstly, in terms of the open circuit potential (OCP) and the extent to which polarity of the galvanic Corrosion cell formed between relevant phases permits FFC propagation, and secondly in terms of the relative susceptibility of the various phases to anodic dissolution. It is concluded that even when FFC is feasible thermodynamically, propagation rates may be negligible due to the low activity for anodic dissolution of tin and iron-tin intermetallics. © The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any
Hamilton Neil Mcmurray - One of the best experts on this subject based on the ideXlab platform.
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The Kinetics and Mechanism of Filiform Corrosion occurring on Zinc-Aluminium-Magnesium coated steel
Corrosion Science, 2019Co-Authors: N. Wint, Geraint Williams, Emmanouela Michailidou, D. Eaves, A. Bennett, Justin Searle, Hamilton Neil McmurrayAbstract:Abstract This paper describes a systematic study into the initiation and propagation of Filiform Corrosion (FFC) on industrially important Zinc-Aluminium-Magnesium (ZAM) alloy coatings for steels. An artificial scribe defect is created in model organic coatings applied to ZAM. Corrosion is initiated using HCl, NaCl, FeCl2 and acetic acid. Only acetic acid is able to reproducibly initiate FFC. The FFC (area) rate is shown to be proportional to the amount of acetic acid introduced. The FFC mechanism is explained in terms of the relative susceptibility of alloy phases to anodic dissolution, determined using scanning electron microscopy and scanning Kelvin probe force microscopy.
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Inhibition of Filiform Corrosion on Organic-Coated Magnesium-Containing Galvanized Steel by Smart-Release Ion Exchange Pigments
ECS Transactions, 2017Co-Authors: Emmanouela Michailidou, Hamilton Neil Mcmurray, Geraint WilliamsAbstract:This paper describes a systematic kinetic study on the inhibitory effect of anion exchange Hydrotalcite-based pigments on Filiform corroding hot dipped Zn-(1-2 w%)Mg-(1-2 w%)Al galvanized steel. Filiform Corrosion was initiated via scribing the organic-coated samples and introducing a corrosive electrolyte in the defect. Following Filiform Corrosion initiation, the time-dependent extent of coating delamination was determined photographically over a period of six weeks. It is positively demonstrated that the addition of smart-release pigments in the organic coating greatly suppresses the rate of Filiform Corrosion. The inhibitor efficiency is shown to increase in the order: carbonate < benzotriazole < benzotriazolate. The release of carbonates leads to Filiform Corrosion increase.
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The Kinetics and Mechanism of Atmospheric Corrosion Occurring on Tin and Iron-Tin Intermetallic Coated Steels II. Filiform Corrosion
Journal of The Electrochemical Society, 2015Co-Authors: N. Wint, Geraint Williams, Hamilton Neil Mcmurray, A.c.a. De VooysAbstract:This paper describes a systematic study into the initiation and propagation of Filiform Corrosion (FFC) on pure iron, pure tin and industrially important tin and iron-tin intermetallic (FeSn and FeSn2) coatings for packaging steels, as a function of coating weight. The time-dependent extent of FFC was determined optically. FFC was not observed on pure tin or tin coatings but was found to propagate at significantly reduced rates on the FeSn and FeSn2 intermetallic coatings, when compared to pure iron. An explanation of the findings is given, firstly, in terms of the open circuit potential (OCP) and the extent to which polarity of the galvanic Corrosion cell formed between relevant phases permits FFC propagation, and secondly in terms of the relative susceptibility of the various phases to anodic dissolution. It is concluded that even when FFC is feasible thermodynamically, propagation rates may be negligible due to the low activity for anodic dissolution of tin and iron-tin intermetallics. © The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any
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The effect of oxygen partial pressure on the Filiform Corrosion of organic coated iron
Corrosion Science, 2014Co-Authors: Trystan Watson, Geraint Williams, A.j. Coleman, Hamilton Neil McmurrayAbstract:An in-situ time-lapse optical microscopy study, using a novel dual-compartment cell is used to gain mechanistic understanding of Filiform Corrosion (FFC) affecting an organic-coated iron surface. The apparatus allows independent control of environments surrounding the filament head and tail regions. When oxygen-containing environments surround the filament head, an anterior cathodic arc is formed, constraining the filament head electrolyte. When oxygen is removed from the vicinity of the head, FFC propagation rates remain unchanged, although the constraining arc is not present. Maximum propagation is observed when oxygen is available for transport through the filament tail to the rear of the head.
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Inhibition of Filiform Corrosion on organic-coated AA2024-T3 by smart-release cation and anion-exchange pigments
Electrochimica Acta, 2012Co-Authors: Geraint Williams, Hamilton Neil McmurrayAbstract:Abstract In-coating cation and anion exchange pigments are studied with respect to their ability to inhibit chloride-induced Filiform Corrosion (FFC) on organic-coated AA2024-T3 aluminium alloy substrates. In-situ scanning Kelvin probe potentiometry is used to quantify both underfilm potentials associated with populations of propagating Corrosion filaments and the kinetics of coating disbondment. Smart-release bentonite pigments containing exchangeable cerium (III) and yttrium (III) cations are shown to be largely ineffective in reducing rates of FFC propagation. The reasons for this are discussed in terms of the chemistry of the electrolyte-filled Corrosion filament head. In contrast, anion-exchange hydrotalcite (HT) based pigments are highly effective inhibitors of FFC. A comparison of the extent of FFC observed for various inorganic exchangeable anions is made with as-received HT comprising carbonate anions. Of the anions evaluated, exchangeable chromate unsurprisingly provides the highest FFC inhibition efficiency. It is also demonstrated that exchanging the native carbonate ions for certain organic species which act as complexing agents for copper ions, gives rise to an equivalent level of FFC inhibition. The implication of these findings with respect to the mechanism of FFC on copper containing aluminium alloys is considered.
Anne-pascale Romano - One of the best experts on this subject based on the ideXlab platform.
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Investigation by electrochemical impedance spectroscopy of Filiform Corrosion of electrocoated steel substrates
Progress in Organic Coatings, 2015Co-Authors: Anne-pascale Romano, Marie-georges OlivierAbstract:Abstract This work aims at studying by electrochemical impedance spectroscopy (EIS) the susceptibility to Filiform Corrosion of low carbon steel covered by cataphoretic coating. The determination of the exposed metallic area variations of scratched samples during ageing test is an estimation of the disbonding of the coating and/or the Filiform Corrosion. This area can be evaluated by electrochemical impedance spectroscopy (EIS). A simplified electrical equivalent model used to estimate the exposed metallic area is valid if the Corrosion products are correctly dissolved before characterization. Furthermore the steel is a very complex substrate and thus many parameters must be optimized in order to remove the Corrosion products before EIS measurements.
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Filiform Corrosion of electrocoated aluminium alloy: Role of surface pretreatment
Corrosion Science, 2012Co-Authors: Andrej Nazarov, Dominique Thierry, Flavio Deflorian, Michele Fedel, Anne-pascale Romano, Marie-georges OlivierAbstract:Abstract Commercial Oxsilan, 3-aminopropyltriethoxysilane and sol–gel siloxane coatings were applied on AA6016 aluminium alloy before electrocoating. Standard Filiform Corrosion test demonstrated the pre-treatment role on the under-paint Corrosion rate. All pre-treatments increase the coating adhesion in water electrolyte (EIS). Anodic undermining is the mechanism of the coatings de-adhesion (SKP). Electromotive force (difference in potentials of defect-surrounding interface) and interface ability to promote the chloride migration are rate-determining factors of the Filiform Corrosion. Contrary to other pre-treatments, the aminosiloxane decreases the interfacial potential, facilitates the chlorides migration and leads to anodic de-adhesion of large coated areas (Tof-SIMS and EDXS).
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silane sol gel film as pretreatment for improvement of barrier properties and Filiform Corrosion resistance of 6016 aluminium alloy covered by cataphoretic coating
Progress in Organic Coatings, 2011Co-Authors: Anne-pascale Romano, M Fedel, F Deflorian, Marie-georges OlivierAbstract:Abstract The aim of this study is to develop a newly silane sol–gel pretreatment on the barrier properties and Filiform Corrosion resistance of 6016 aluminium alloy covered by cataphoretic coating. The sol–gel coatings are used as coupling agent between aluminium substrate and cataphoretic paint. The pretreatment is an aqueous solution of three different silane compounds (glycidyloxypropyltrimethoxysilane (GPS), tetraethoxysilane (TEOS) and methyltriethoxysilane (MTES)) hydrolysed at two different pH (2 and 3.5). A system without pretreatment was studied as reference. The electrocoatings were cured between 155 °C and 195 °C in order to modify their mechanical properties. Polarisation curves, EIS and FT-IR measurements were used in order to characterize the silane layers. EIS measurements were used to follow the barrier properties and the water uptake evolution on intact coatings. The Filiform Corrosion protection of the coating was also evaluated by a normalized Filiform Corrosion test.
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Silane sol–gel film as pretreatment for improvement of barrier properties and Filiform Corrosion resistance of 6016 aluminium alloy covered by cataphoretic coating
Progress in Organic Coatings, 2011Co-Authors: Anne-pascale Romano, Flavio Deflorian, Michele Fedel, Marie-georges OlivierAbstract:Abstract The aim of this study is to develop a newly silane sol–gel pretreatment on the barrier properties and Filiform Corrosion resistance of 6016 aluminium alloy covered by cataphoretic coating. The sol–gel coatings are used as coupling agent between aluminium substrate and cataphoretic paint. The pretreatment is an aqueous solution of three different silane compounds (glycidyloxypropyltrimethoxysilane (GPS), tetraethoxysilane (TEOS) and methyltriethoxysilane (MTES)) hydrolysed at two different pH (2 and 3.5). A system without pretreatment was studied as reference. The electrocoatings were cured between 155 °C and 195 °C in order to modify their mechanical properties. Polarisation curves, EIS and FT-IR measurements were used in order to characterize the silane layers. EIS measurements were used to follow the barrier properties and the water uptake evolution on intact coatings. The Filiform Corrosion protection of the coating was also evaluated by a normalized Filiform Corrosion test.
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influence of crosslinking density of a cataphoretic coating on initiation and propagation of Filiform Corrosion of aa6016
Progress in Organic Coatings, 2009Co-Authors: Anne-pascale Romano, Andrej Nazarov, Marie-georges Olivier, Dominique ThierryAbstract:The effect of curing temperature on initiation and propagation of Filiform Corrosion of an epoxy cataphoretic electrocoating deposited on aluminum alloy substrate was studied. EIS measurements were used to follow the evolution of the water uptake of the intact coatings. In addition, EIS was applied to determine the performances of the systems as a result of exposure to HCl vapours. Cantilever method (stressmeter) was used to determine the stresses generated in an organic coating during a humidity cycle. Scanning Kelvin Probe (SKP) was applied in order to investigate the initiation and propagation of Filiform Corrosion of painted aluminum alloy. The mechanism of Filiform Corrosion is discussed according to the paint properties.
Kemal Nisancioglu - One of the best experts on this subject based on the ideXlab platform.
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Formation 01 Nanocrystalline Surtace Layers by Annealing and Their Role in Filiform Corrosion of Aluminum Sheet
2016Co-Authors: Hâkon Lethoisen, Jan Halvor A Nordlien, Kemal NisanciogluAbstract:Annealing of specific rolled aluminum alloys at temperatures above 300°C causes a significant increase in the Filiform Corrosion sus-ceptibility of the painted substrate. As demonstrated for a selected substrate (AA8006), the increased susceptibility is related to the for-mation of a thin, (electro-)chemically active nanocrystalline layer at the surface as a result of the annealing treatment. The Corrosion resist-ance is significantly improved by removing the layer by etching during surface treatment. Possible causes of layer formation and its activity are discussed
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Filiform Corrosion of binary aluminium model alloys
Corrosion Science, 2002Co-Authors: Andreas Afseth, G.m. Scamans, Jan Halvor Nordlien, Kemal NisanciogluAbstract:The effect of alloy composition and microstructure on Filiform Corrosion (FFC) susceptibility was investigated for super-purity based binary model alloys of the systems Al–Mg, Al– Mn, Al–Fe and Al–Cu. Corrosion testing indicated that the presence of electrochemically noble second phase particles is a necessity for FFC to occur. Single phase, solid solution alloys of the Al–Mg, Al–Mn or Al–Fe systems did not support FFC. Heat treatment caused precipitation of the electrochemically noble intermetallic phase FeAl3 in the Al–Fe alloy, resulting in extensive FFC. Precipitation of the phase MnAl6, which has electrochemical properties similar to that of the aluminium rich matrix, by heat treatment did not impair the Corrosion properties of the Al–Mn alloy. Significant surface oxidation and magnesium enrichment of the surface oxides by heat treatment did not affect the FFC properties of Al–Mg alloys. However, the solid solution binary Al–Cu alloys exhibited severe FFC. The detrimental effect of copper in solid solution is attributable to selective dissolution phenomena during the Corrosion process, whereby copper was locally enriched on the surface as copper-rich particles providing efficient cathodic sites. � 2002 Elsevier Science Ltd. All rights reserved.
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Filiform Corrosion of AA3005 aluminium analogue model alloys
Corrosion Science, 2002Co-Authors: Andreas Afseth, G.m. Scamans, Jan Halvor Nordlien, Kemal NisanciogluAbstract:Abstract The effect of the metal substrate microstructure on Filiform Corrosion (FFC) susceptibility was investigated for super purity based model alloys with compositions based on the specifications of AA3005. Variations in alloying levels of the elements iron, silicon and copper were investigated. Alloys with high silicon content were more susceptible to FFC than alloys with low silicon content. The iron content, at the levels investigated, did not strongly affect FFC properties. The apparent detrimental effect of a high silicon content is attributed to the influence of silicon on secondary intermetallic particle precipitation. Given the same thermo-mechanical treatment, alloys with high silicon content underwent more extensive secondary precipitation of manganese containing intermetallic particles than those alloys with a low silicon content. The resulting microstructure is characterised by a higher density of finely dispersed intermetallic particles and a lower content of manganese in the adjacent supersaturated solid solution. These conditions provide a large number of potential Corrosion initiation sites on the surface and also enhance microgalvanic coupling between intermetallic particles and the surrounding aluminium rich matrix, thus promoting the propagation of filamental Corrosion attacks. Additions of copper had a detrimental effect on the FFC resistance. The role of copper in promoting FFC is attributed to preferential dissolution phenomena during the Corrosion process, whereby copper is locally enriched on the corroding surface. This copper enrichment provides additional area for cathodic reaction, thus enhancing the Corrosion process.
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Effect of thermo-mechanical processing on Filiform Corrosion of aluminium alloy AA3005
Corrosion Science, 2002Co-Authors: Andreas Afseth, G.m. Scamans, Jan Halvor Nordlien, Kemal NisanciogluAbstract:The effect of laboratory scale thermo-mechanical processing of aluminium alloy AA3005, supplied as 2.9 mm sheet at the hot roll transfer gauge, on Filiform Corrosion (FFC) susceptibility, electrochemical properties and near surface microstructure was investigated. Corrosion testing showed that the as hot rolled material exhibited poor FFC resistance and that heat treatment of both the as hot rolled and subsequently cold rolled samples resulted in a drastic loss of Corrosion resistance. Microstructural characterisation showed that both hot and cold rolling resulted in enhanced surface shear deformation and the formation of a thin layer of metal in the surface with different properties and microstructural characteristics than the underlying bulk material. Enhanced surface deformation resulted in a redistribution of intermetallic particles in this region. Poor FFC properties were correlated with the presence of a higher density of fine intermetallic precipitates in the surface layers than in the underlying bulk. It is suggested that enhanced secondary precipitation of intermetallic particles in the deformed surface layers during high temperature exposure, e.g., during hot rolling or annealing steps, is the main contributing factor to the observed poor FFC resistance.
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Influence of heat treatment and surface conditioning on Filiform Corrosion of aluminium alloys AA3005 and AA5754
Corrosion Science, 2001Co-Authors: Andreas Afseth, G.m. Scamans, Jan Halvor Nordlien, Kemal NisanciogluAbstract:Abstract The effect of high-temperature heat treatment combined with different cleaning and pre-treatment practices on Filiform Corrosion resistance has been investigated for aluminium alloys AA3005 and AA5754. High-temperature heat treatment severely reduces the Filiform Corrosion resistance of alloy AA3005, while the Corrosion properties of alloy 5754 are only moderately affected. The drastic loss of Filiform Corrosion resistance of alloy AA3005 after high-temperature heat treatment is attributed to preferential microstructural changes in a heavily deformed, micrograined surface layer caused by large surface shear strain during rolling. The enhanced deformation of the near-surface region promotes precipitation of a fine dispersion of intermetallic particles during subsequent heat treatment. The higher density of intermetallic particles combined with lower supersaturated solid solution levels of manganese in the surface layer as compared to the bulk structure makes the heat-treated AA3005 material susceptible to superficial Corrosion attacks and results in poor Filiform Corrosion resistance. Application of a commercial acid cleaning/chromating pre-treatment did not restore the Filiform Corrosion resistance of heat-treated alloy AA3005. Alloy AA5754, containing lower levels of manganese and iron than AA3005, did not undergo similar preferential microstructural changes during heat treatment. A moderate increase in the amount of Filiform Corrosion of heat-treated AA5754 samples is attributed to poor protective properties of the thick, magnesium enriched, thermally formed surface oxide on this alloy. Any cleaning/pre-treatment practice that removes the thermally formed oxide on this alloy results in a very high Filiform Corrosion resistance.