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The micro-galvanic interactions between Cu-Fe-Mn-Li-containing aluminides and the alloy matrix of aluminium alloy AA2099 during chloride-induced corrosion were investigated in-situ with real-time monitoring of the local contact potential difference (VCPD) using the scanning Kelvin probe force microscopy (SKPFM) at controlled relative humidities. The aluminides showed noble potentials and were able to ennoble their neighbouring matrix sites when a cluster of aluminides surrounded the matrix. The matrix, hence, adopted a more positive VCPD, towards that of the aluminides. The anode-to-cathode ratio changed throughout the corrosion exposure and was seen to show a dynamic character. Much higher local VCPD activities were recorded during the earliest stages of corrosion, when the Al-Li AA2099 surface was first exposed to high humidities, than in later RH cycles, a phenomenon not seen in other aluminium alloys.
Yanhan Liew; Cem Örnek; Jinshan Pan; Dominique Thierry; Sudesh Wijesinghe; Daniel J. Blackwood. Towards understanding micro-galvanic activities in localised corrosion of AA2099 aluminium alloy. Electrochimica Acta 2021, 392, 139005 .
AMA StyleYanhan Liew, Cem Örnek, Jinshan Pan, Dominique Thierry, Sudesh Wijesinghe, Daniel J. Blackwood. Towards understanding micro-galvanic activities in localised corrosion of AA2099 aluminium alloy. Electrochimica Acta. 2021; 392 ():139005.
Chicago/Turabian StyleYanhan Liew; Cem Örnek; Jinshan Pan; Dominique Thierry; Sudesh Wijesinghe; Daniel J. Blackwood. 2021. "Towards understanding micro-galvanic activities in localised corrosion of AA2099 aluminium alloy." Electrochimica Acta 392, no. : 139005.
The light-weight aluminium alloys play an important role in reducing emissions from the transport industry. However, to take full advantage of these, the corrosion mechanisms that govern their failure need to be properly understood. Hence, the electrochemical response, especially after passive film breakdown, of the aluminium alloy AA5083 was analysed via potentiodynamic polarisation. By starting the scans at the relatively negative potential of −1.4 V (vs. SCE), the reduction of water in the electrolyte causes a localised increase in pH, leading to a preferential attack on the susceptible regions in the (sensitised) microstructure; that is, the deleterious β-Al3Mg2 along the grain boundaries. Subsequently, in the later stages of the potentiodynamic scan, these regions that have been degraded by the dissolution of β-Al3Mg2 undergo imperfect repassivation, leading them to be vulnerable to localised breakdowns. These conditions allowed for the discovery of a discernible trend after breakdown, in which AA5083 microstructures with a more extensive β-Al3Mg2 region (both in size and in amount) recorded a more rapid increase in the measured current density. In particular, the potential at which the anodic current density reached 1 × 10−4 A cm−2 was correlated with the extent of β-Al3Mg2 formed during isothermal heat-treatments. This work provides a possible pathway towards the development of an electrochemical quantification technique for the extent of β-Al3Mg2 growth, degree of sensitisation, and, ultimately, the intergranular corrosion (IGC) susceptibility of the microstructure of AA5083 components used in industrial applications.
Yanhan Liew; Sudesh Wijesinghe; Daniel Blackwood. Investigation of the Electrochemical Breakdown Response in Sensitised AA5083 Aluminium Alloy. Sustainability 2021, 13, 7342 .
AMA StyleYanhan Liew, Sudesh Wijesinghe, Daniel Blackwood. Investigation of the Electrochemical Breakdown Response in Sensitised AA5083 Aluminium Alloy. Sustainability. 2021; 13 (13):7342.
Chicago/Turabian StyleYanhan Liew; Sudesh Wijesinghe; Daniel Blackwood. 2021. "Investigation of the Electrochemical Breakdown Response in Sensitised AA5083 Aluminium Alloy." Sustainability 13, no. 13: 7342.
Sensitized AA5083-H2 was exposed to chloride-laden thin-film electrolyte at ambient temperature (20-85% relative humidity) and the local Volta potential measured, in-situ and in real-time, using the Scanning Kelvin Probe Force Microscopy, with the intention to elucidate the earliest stage of localized corrosion . Positive Volta potentials (vs matrix) were measured for magnesium silicides in ambient air, which, however, underwent a severe nobility loss during corrosion, causing their nobility to invert to active potentials (negative) relative to the alloy matrix. The reason for the nobility inversion was explained by the preferential dissolution of Mg2+, which resulted in an electropositive surface. Aluminides, both with and without silicon, were seen to form the main cathodes at all exposure conditions. The local alloy matrix next to closely-separated aluminides were seen to adopt the Volta potential of the neighbor aluminides, which, hence, resulted in local corrosion protection. The phenomenon of nobility adoption introduced here raises questions regarding the anode-to-cathode ratio, which was observed to change during corrosion, and the resulting impact to localized micro-galvanic corrosion. This work further demonstrates that it is necessary to measure the Volta potential during corrosion to reflect the true relationship between the Volta potential and corrosion potential or breakdown potential.
Yanhan Liew; Cem Örnek; Jinshan Pan; Dominique Thierry; Sudesh Wijesinghe; Daniel John Blackwood. In-Situ Time-Lapse SKPFM Investigation of Sensitized AA5083 Aluminum Alloy to Understand Localized Corrosion. Journal of The Electrochemical Society 2020, 167, 141502 .
AMA StyleYanhan Liew, Cem Örnek, Jinshan Pan, Dominique Thierry, Sudesh Wijesinghe, Daniel John Blackwood. In-Situ Time-Lapse SKPFM Investigation of Sensitized AA5083 Aluminum Alloy to Understand Localized Corrosion. Journal of The Electrochemical Society. 2020; 167 (14):141502.
Chicago/Turabian StyleYanhan Liew; Cem Örnek; Jinshan Pan; Dominique Thierry; Sudesh Wijesinghe; Daniel John Blackwood. 2020. "In-Situ Time-Lapse SKPFM Investigation of Sensitized AA5083 Aluminum Alloy to Understand Localized Corrosion." Journal of The Electrochemical Society 167, no. 14: 141502.
The intergranular corrosion susceptibility of AISI 304L stainless steel can be measured in the field using the single loop electrochemical potentiokinetic reactivation test. However, the present work questions the reliability of the test, with nominally the same as-received samples given a wide range of degrees of sensitization, enough for opposite conclusions and potentially false positive results. More worryingly, when comparing the results to the oxalic acid etch test, a false negative result of the SL-EPR test was obtained on some heat-treated samples. This could entail serious repercussions and justifies a thorough investigation into this issue. The most likely explanation for the unexpected behavior of one batch of 304L, is its moderate silicon enrichment at 0.4 wt%. As long as the stainless steel does not exceed the passive region, as is the case for the SL-EPR test, the moderate silicon additions help suppress intergranular corrosion, but in the strongly oxidizing environment of the oxalic acid test the stainless steel becomes transpassive and the silicon results in accelerated corrosion of the grain boundaries.
Yan Han Liew; Daniel J. Blackwood; Sudesh Wijesinghe. Contradictory Results from Single Loop Electrochemical Potentiokinetic Reactivation Test and Oxalic Acid Test for Intergranular Corrosion in 304L Stainless Steels Attributed to Si Grain-Boundary Segregation. Journal of The Electrochemical Society 2019, 166, C410 -C420.
AMA StyleYan Han Liew, Daniel J. Blackwood, Sudesh Wijesinghe. Contradictory Results from Single Loop Electrochemical Potentiokinetic Reactivation Test and Oxalic Acid Test for Intergranular Corrosion in 304L Stainless Steels Attributed to Si Grain-Boundary Segregation. Journal of The Electrochemical Society. 2019; 166 (13):C410-C420.
Chicago/Turabian StyleYan Han Liew; Daniel J. Blackwood; Sudesh Wijesinghe. 2019. "Contradictory Results from Single Loop Electrochemical Potentiokinetic Reactivation Test and Oxalic Acid Test for Intergranular Corrosion in 304L Stainless Steels Attributed to Si Grain-Boundary Segregation." Journal of The Electrochemical Society 166, no. 13: C410-C420.