Inhibition of Filiform Corrosion on Organic-Coated Aluminum Alloy by Hydrotalcite-Like Anion-Exchange Pigments

CORROSION ◽  
2004 ◽  
Vol 60 (3) ◽  
pp. 219-228 ◽  
Author(s):  
H. N. McMurray ◽  
G. Williams
Keyword(s):  
Aluminum Alloy ◽  
Anion Exchange ◽  
Polyvinyl Butyral ◽  
Kelvin Probe ◽  
Free Corrosion Potential ◽  
Filiform Corrosion ◽  
Coating Delamination ◽  
Coating Defect ◽  
Aluminum Alloy 2024

Abstract Novel anion-exchange anticorrosion pigments consisting of nitrate-, carbonate-, and chromate-exchanged hydrotalcite (HT) are shown to inhibit the propagation of filiform corrosion (FFC) effectively on organic-coated aluminum alloy 2024-T3 (AA2024-T3 [UNS A92024]) alloy. The HT-pigments are dispersed in polyvinyl butyral (PVB) coatings applied to the AA2024-T3 surface. Following FFC initiation by application of controlled amounts of aqueous hydrochloric acid (HCl) to a penetrative coating defect, the time-dependent extent of coating delamination is determined both optically and by repeated in-situ scanning using a scanning Kelvin probe (SKP) apparatus. All the HT-pigments profoundly reduce rates of coating delamination by comparison to unpigmented samples. However, inhibitor efficiency is dependent upon the exchangeable anion and increases in the order: carbonate < nitrate < chromate. It is also shown that by using SKP potentiometry, exchangeable chromate anions interact specifically with the metal surface to depress free corrosion potential values.

Filiform Corrosion on 6000 Series Aluminium: Kinetics and Inhibition Strategies

2006 ◽  
Vol 519-521 ◽  
pp. 629-634 ◽  
Author(s):  
A.J. Coleman ◽  
H.N. McMurray ◽  
G. Williams ◽  
Andreas Afseth ◽  
Geoff M. Scamans
Keyword(s):  
Time Lapse ◽  
Kelvin Probe ◽  
Surface Shear ◽  
Free Corrosion Potential ◽  
Fine Grained ◽  
Filiform Corrosion ◽  
Coated Alloy ◽  
Coating Delamination ◽  
Paint Films

High levels of surface shear experienced during rolling, grinding or machining can cause 6000 series aluminium to develop an ultra-fine grained surface layers which dramatically increase susceptibility to filiform corrosion (FFC) under paint films. In-situ Scanning Kelvin Probe (SKP) measurements in humid air are used to compare the kinetics and mechanism of FFC on abraded and lacquer-coated samples of high copper containing AA6111 and low level copper AA6016. FFC is initiated by applying a small volume of aqueous HCl to a penetrative defect on polyvinylbutyral (PVB) coated alloy samples prior to placement in a chamber maintained at constant humidity and temperature. The SKP is then repeatedly scanned over a fixed surface area to produce a time-lapse animation showing the dynamic evolution of localized free corrosion potential patterns. The spatial distribution of potential variation provides insight into the FFC mechanism and the numerical integration of areas of dissimilar potential provides a measure of the time-dependent area of coating delamination. Various possible FFC inhibition strategies are investigated for use under circumstances where removal of the surface layer prior to application of an organic (paint) coating is not feasible. The two strategies shown in this paper are the use of an anti-corrosion pigments based on an intrinsically conducting polymer called polyaniline. An anion-exchange pigment called hydrotalcite is also used.

scholarly journals A mechanistic investigation of corrosion-driven organic coating failure on magnesium and its alloys

2019 ◽  
Vol 3 (1) ◽  
Author(s):  
Geraint Williams ◽  
Christos Kousis ◽  
Neil McMurray ◽  
Patrick Keil
Keyword(s):  
Hydrogen Evolution ◽  
Ionic Current ◽  
Time Lapse ◽  
Organic Coating ◽  
Kelvin Probe ◽  
Group I ◽  
Mechanistic Investigation ◽  
Filiform Corrosion ◽  
Coating Delamination ◽  
Chloride Salts

AbstractThe failure mechanism of model organic coatings from Mg alloy surfaces is characterised by a combination in-situ scanning Kelvin probe analysis and time lapse photography. Initiation of underfilm corrosion by application of group I chloride salts to a penetrative coating defect produces an apparent cathodic-driven coating delamination, where the disbondment distance increases linearly with time at high relative humidity, although filiform corrosion (FFC) is also observed in the vicinity of the defect. The disbondment process occurs both in the presence and absence of oxygen, indicating that hydrogen evolution comprises the predominant underfilm cathodic reaction. Post-corrosion elemental analysis of the delaminated region shows an abundance of group I cation, but no chloride. When magnesium chloride or HCl are used to initiate corrosion, then only FFC is produced. The mechanism is discussed in terms of net anodic dissolution at the defect coupled with underfilm cathodic hydrogen evolution, producing organic coating disbondment under conditions where cations are able to transport ionic current within a zone of increased pH.

In-Situ Monitoring of Pitting Corrosion in Aluminum Alloy 2024

CORROSION ◽  
1998 ◽  
Vol 54 (6) ◽  
pp. 451-458 ◽  
Author(s):  
C.-M. Liao ◽  
J. M. Olive ◽  
M. Gao ◽  
R. P. Wei
Keyword(s):  
Aluminum Alloy ◽  
Pitting Corrosion ◽  
In Situ Monitoring ◽  
Aluminum Alloy 2024

scholarly journals In situ structural characterization of ageing kinetics in aluminum alloy 2024 across angstrom-to-micrometer length scales

2016 ◽  
Vol 111 ◽  
pp. 385-398 ◽  
Author(s):  
Fan Zhang ◽  
Lyle E. Levine ◽  
Andrew J. Allen ◽  
Carelyn E. Campbell ◽  
Adam A. Creuziger ◽  
...  
Keyword(s):  
Aluminum Alloy ◽  
Structural Characterization ◽  
Length Scales ◽  
Aluminum Alloy 2024

Scanning Kelvin Probe Studies of Filiform Corrosion on Automotive Aluminum Alloy AA6016

2007 ◽  
Vol 154 (7) ◽  
pp. C339 ◽  
Author(s):  
H. N. McMurray ◽  
A. J. Coleman ◽  
G. Williams ◽  
A. Afseth ◽  
G. M. Scamans
Keyword(s):  
Aluminum Alloy ◽  
Kelvin Probe ◽  
Scanning Kelvin Probe ◽  
Filiform Corrosion

Scanning Kelvin Probe Studies of Cosmetic (Filiform) Corrosion on AA6016

2006 ◽  
Vol 519-521 ◽  
pp. 679-686 ◽  
Author(s):  
H.N. McMurray ◽  
A.J. Coleman ◽  
G. Williams ◽  
Andreas Afseth ◽  
Geoff M. Scamans
Keyword(s):  
Heat Treatment ◽  
Surface Layer ◽  
Polyvinyl Butyral ◽  
Open Circuit ◽  
Grain Structure ◽  
Metal Loss ◽  
Kelvin Probe ◽  
Fine Grain ◽  
Scanning Kelvin Probe ◽  
Filiform Corrosion

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 difference between the surface layer and the bulk provides and increased thermodynamic driving force for corrosion. For post-abrasion heat treatment temperatures up to 350°C the fast filiform process is followed by a slower, deeper form of FFC.

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