Cathodic Control of Intergranular Corrosion Propagation in Al-Mg Alloys Under Thin Film Conditions

Khullar, Piyush; Badilla, J. V.; Kelly, Robert G.

doi:10.5006/2171

Cited by 7 publications

(4 citation statements)

References 8 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…It must be mentioned that the same comparison between immersion and atmospheric (droplet) conditions showed that under free corrosion conditions, for other aluminum alloy series (5xxx), kinetics of cathodic reactions on outer surface of specimens seemed to also control the rate of IGC. 33 This cathodic control of the propagation resulting from the surface microstructure could be one of the factors explaining the stochastic nature of IGC propagation under free corrosion conditions. Indeed, the cathodes (coarse intermetallic particles) were statistically distributed at the surface.…”

Section: Simulation Under Free Corrosion Conditions and Discussion-mentioning

confidence: 99%

Optical and Chemical Monitoring during Foil Penetration Experiments to Study Intergranular Corrosion in AA2024

Bonzom

Oltra

2018

J. Electrochem. Soc.

View full text Add to dashboard Cite

A modified version of the foil penetration technique based on an optical detection of the full penetrating intergranular defects through thin foils was applied to AA2024 samples of various thicknesses in contact with a dilute chloride solution. As the rear side of the foil was free during the experiments, it was straightforward to measure the pH of the electrolyte trapped inside the grain boundary network leaking through the emerging defects on the rear side of the foils. The penetration regime in the longitudinal direction was determined for various exposure and electrochemical conditions confirming the decrease of the propagation kinetics as function of the depth of the intergranular defects. pH measurements were used to support mass transport simulation inside a pore electrode mimicking the propagation of the anodic head of grain boundaries. After validation under potentiostatic conditions, the same modelling approach was applied under free corrosion conditions, to discuss the location of cathodic areas during immersion and droplet exposures. Frankel and coworkers 1 considered the anisotropy of the intergranular corrosion process and performed foil penetration tests using various electrochemical conditions. They proposed that the propagation rate of intergranular corrosion followed a power law of the following type:where d is either the nominal thickness of the full penetrated foil or the resulting IG path length, a and n are constants (n is between 0 and 1) and t the time for the full penetration. To discuss these results in terms of IG propagation rate the raw data can be inverted and expressed as the depth of the fastest growing site as a function of time. However the physical meaning of the exponent and its value as function the nature of the alloy have not been discussed to our knowledge. Nevertheless, interesting work described in Ref. 2 illustrated application of such a law (relation 1) deduced from laboratory experiments to operational aircraft. In these practical cases there was a large variation in corrosion growth rates from one section of a wing to the next or from an aircraft to the next. But it was demonstrated that it was possible to provide a distribution for coefficients of relation (1), especially for coefficient a, which could be deduced from documented corrosion data collected, for example, from repair data.Relation (1) which means that the intergranular (IG) propagation rate on aluminum alloys (AA2024) is decreasing as function of the IG path length has been validated under potentiostatic conditions. 1 Moreover this trend has been also frequently discussed in other studies under free corrosion conditions. 3,4 Nevertheless, the origin of this feature has not been largely discussed quantitatively, especially as the inner surface of the "IG crevice" behind the active anodic head at the point of attack 5 can also suffer dissolution at a reduced rate and at long exposures as illustrated in different works showing a blunting of the IG path.6,7 Consequently the mass transport and/or the ohmic dr...

show abstract

Section: Simulation Under Free Corrosion Conditions and Discussion-mentioning

confidence: 99%

Optical and Chemical Monitoring during Foil Penetration Experiments to Study Intergranular Corrosion in AA2024

Bonzom

Oltra

2018

J. Electrochem. Soc.

View full text Add to dashboard Cite

show abstract

“…This phenomenon is due to the insufficient cathode current available in this small area. 49 The potential distribution was then used to predict the IGC damage 45 based on the known dependence of IGC rate on potential. 48 Figure 10(c) shows the comparison of the modeling using the Laplace equation as the governing law with chlorideconcentration-dependent electrode kinetics.…”

Section: Use Of the Laplace Equationmentioning

confidence: 99%

2021 W.R. Whitney Award: The Importance of Local Chemistry and Potential in Localized Corrosion and Stress Corrosion Cracking

Kelly¹

2021

Corrosion

View full text Add to dashboard Cite

The nature and rates of the chemical and electrochemical reactions that occur within the occluded regions of a given alloy are controlled by the local electrochemical potential and the local solution composition. The very small physical dimensions of these regions lead to challenges in both measurement and modeling. When performed in a coordinated and complementary way, measurements and modeling provide insights into the controlling processes of a range of localized corrosion phenomena, including crevice corrosion, pitting, intergranular corrosion, and stress-corrosion cracking. Examples of attempts to overcome the measurement challenges are described for a range of corrosion scenarios, including identification of the critical ionic species in stainless steel crevice corrosion and in the corrosion of aircraft lap joints, operando measurement of chemistry and potential simultaneously within stress-corrosion cracks, and monitoring of water layer thickness in salt spray testing. Examples of work addressing the challenges in modeling localized corrosion including intergranular corrosion of AA5XXX alloys, scaling laws in crevice corrosion, the extent to which the Laplace Equation can be used and applied to geometrically complex galvanic structures, and an approach to modeling localized corrosion for extraordinarily long service times. Finally, suggestions regarding future avenues of research are provided.

show abstract

“…a continuous planar film vs. a discrete hemispherical cap vs. secondary spreading film emanating from hemispherical caps) [19][20][21], the salt identity, salt loading density (mass per area) and the relative humidity. By influencing the thickness of this film, salt loading can critically influence galvanic coupling [22,23], pit growth and stability [24], crevice propagation [25], intergranular corrosion [26], and so forth. For this reason, assessment of atmospheric chloride deposition is crucial for predicting the service lifetime of many engineering structures such as bridges, automobiles, planes, ships and buildings.…”

Section: Introductionmentioning

confidence: 99%

Atmospheric corrosion severity and the precision of salt deposition measurements made by the wet candle method

Santucci

Davis

Sanders

2021

Corrosion Engineering, Science and Technology

View full text Add to dashboard Cite

The Wet Candle technique quantifies the dry deposition flux of atmospheric species onto a gauze wick. Salt deposition flux is used to rate the corrosion severity of outdoor test sites. It is important to quantify the precision of the Wet Candle method if the results are used to compare the atmospheric corrosivity of various sites. An analysis of Wet Candle precision is conducted in terms of repeatability and reproducibility. The percent deviation is 3.2% for chloride repeatability and 3.3% for chloride reproducibility. Interval testing is conducted to determine if weekly intervals added together yield a deposition flux similar to a month-long interval. Weekly results are assessed alongside meteorological data to correlate atmospheric conditions to dry deposition. Finally, the erroneous contribution of chloride from various types of gloves to deposition flux is quantified. Based on these findings, recommendations are made on how to avoid various sources of error.

show abstract

Cathodic Control of Intergranular Corrosion Propagation in Al-Mg Alloys Under Thin Film Conditions

Cited by 7 publications

References 8 publications

Optical and Chemical Monitoring during Foil Penetration Experiments to Study Intergranular Corrosion in AA2024

Optical and Chemical Monitoring during Foil Penetration Experiments to Study Intergranular Corrosion in AA2024

2021 W.R. Whitney Award: The Importance of Local Chemistry and Potential in Localized Corrosion and Stress Corrosion Cracking

Atmospheric corrosion severity and the precision of salt deposition measurements made by the wet candle method

Contact Info

Product

Resources

About