In Situ and Operando AFM and EIS Studies of Anodization of Al 6060: Influence of Intermetallic Particles

Zhang, Fan; Nilsson, Jan‐Olov; Pan, Jinshan

doi:10.1149/2.0061610jes

Cited by 55 publications

(38 citation statements)

References 49 publications

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“…This could be the reason why Al 2 CuMg always dissolves first when immersed in corrosive solutions. 27 The results show that, similar to Mg 2 Si, the variation in the calculated Volta potential of Al 2 CuMg is significantly larger than that for Al 2 Inversion of electrochemical nobility.-It has been reported in literature that some experiments revealed an inversion of electrochemical nobility for Mg 2 Si 35,42 and Al 2 CuMg 40 after being corroded. The reason for this phenomenon is believed that elements like Mg and Al, which are much more active than Si and Cu, tend to dissolve initially from the IMPs resulting in Si and Cu enrichment.…”

Section: Resultsmentioning

confidence: 62%

First-Principle Calculation of Volta Potential of Intermetallic Particles in Aluminum Alloys and Practical Implications

Jin

Liu

Zhang

et al. 2017

J. Electrochem. Soc.

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This work presents a theoretical assessment of galvanic (relative) nobility of four intermetallic particles (IMPs), Al 2 Cu, Al 2 CuMg, Mg 2 Si and MgZn 2 , in aluminum alloys through work function calculation based on density functional theory (DFT). The concepts of work function, Volta potential and relative nobility are discussed with respect to the IMPs and aluminum matrix. The calculated Volta potentials are compared with reported experimental Volta potentials measured by scanning Kelvin probe force microscopy (SKPFM). Various crystal faces and terminal types are examined in the DFT calculation, showing that these two factors have a significant effect on the work function value. Considering the large divergence in the reported experimental data, the comparison shows a general agreement between the calculated and experimental Volta potential data for the investigated IMPs. The DFT calculations provide theoretical explanations for several experimental phenomena. The results demonstrate that DFT calculation is a valuable theoretical approach for assessment of the relative nobility of different phases in the alloys, providing complementary information to experimental data from SKFPM. Moreover, the implications of the calculated Volta potentials are discussed with respect to the corrosion potentials. The addition of various alloying elements into the aluminum (Al) matrix to improve mechanical performance of Al alloys may simultaneously increase their susceptibility to localized corrosion. This is mainly due formation of intermetallic particles (IMPs) that may trigger micro-galvanic corrosion along the interface between the IMPs and the alloy matrix.1 The potential differences between the IMPs and the matrix may result in localized dissolution of the matrix or dealloying of the IMP. 2The most common IMPs present in 2xxx and 7xxx series Al alloys include Al 2 CuMg (S-phase), Al 2 Cu (θ-phase), Al 7 Cu 2 Fe (β-phase), MgZn 2 (η-phase) and Mg 2 Si.3-5 IMPs containing Cu and Fe, such as Al 2 Cu. 6 and Al 7 Cu 2 Fe, 7 are considered to be cathodic with respect to the matrix, acting as local cathodes and thus promoting cathodic reactions such as oxygen reduction. In contrast, Mg-rich IMPs, such as Al 2 CuMg, are considered anodic relative to the matrix, resulting in selective dissolution and concomitant Cu-enrichment of the IMP.8 These localized corrosion events may eventually trigger other corrosion forms, such as stress corrosion cracking or intergranular corrosion.9 Therefore, micro-galvanic corrosion effects between IMPs and the Al matrix is considered to be of utmost importance for the overall service performance of Al alloys.In 1987, Stratmann started to use the Kelvin probe to investigate corrosion properties of metals under thin electrolyte films.10 His measurements revealed a linear relationship between Volta potential and corrosion potential of Cu, Zn, Fe and other metals. Later, the scanning Kelvin microprobe was developed and used for Volta potential measurements of several metals in humid atmospheres.11 Du...

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Section: Resultsmentioning

confidence: 62%

First-Principle Calculation of Volta Potential of Intermetallic Particles in Aluminum Alloys and Practical Implications

Jin

Liu

Zhang

et al. 2017

J. Electrochem. Soc.

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“…Therefore, respectively. The arrows indicate that the Mg atom is pulled towards the surface whereas the Si atom is repulsed towards the bulk interior a driving force for localized attack can be expected which indeed is commonly observed in aluminum and magnesium alloys [34,[63][64][65][66].…”

Section: Discussionmentioning

confidence: 85%

Volta Potential Evolution of Intermetallics in Aluminum Alloy Microstructure Under Thin Aqueous Adlayers: A combined DFT and Experimental Study

et al. 2018

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In this work, first-principle density functional theory (DFT) was used to calculate the work function and Volta potential differences between aluminum alloy matrix and two intermetallic phases (Mg 2 Si and Al 2 Cu) with varying surface terminations as a function of adhering monolayers (ML) of water. The calculated data were compared with experimental local Volta potential data obtained by the scanning Kelvin probe force microscopy (SKPFM) on a commercial aluminum alloy AA6063-T5 in atmospheric environments with varying relative humidity (RH). The calculations suggest that the surface termination has a major effect on the magnitude and polarity of the Volta potential of both intermetallic phases (IMP's). The Volta potential difference between the IMP's and the aluminum matrix decreases when the surface is gradually covered by water molecules, and may further change as a function of adhering ML's of water. This can lead to nobility inversions of the IMP's relative to the aluminum matrix. The measured Volta potential difference between both IMP's and their neighboring matrix is dependent on RH. Natural oxidation in ambient indoor air for 2 months led to a nobility inversion of the IMP's with respect to the aluminum matrix, with the intermetallics showing anodic nature already in dry condition. The anodic nature of Al 2 Cu remained with the introduction of RH, whereas Mg 2 Si became cathodic at high RH, presumably due to de-alloying of Mg and oxide dissolution. The DFT calculations predicted an anodic character of both IMP's in reference to the oxidized aluminum matrix, being in good agreement with the SKPFM data. The DFT and SKPFM data were discussed in light of understanding localized corrosion of aluminum alloys under conditions akin to atmospheric exposure.

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“…Both elements are nearly insoluble in the aluminum solid state and the identification of precipitation as an intermetallic AlFeSi‐phase is reasonable. According to the literature, these intermetallics act cathodically to the matrix in case of corrosion …”

Section: Methodsmentioning

confidence: 99%

Corrosion behavior of anodized AA‐6060 depending on the anodizing bath aging

Schneider

Kremmer

2019

Materials & Corrosion

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The present work is concerned with the corrosion behavior of anodized AA‐6060 in chloride containing solutions. The anodic layers were produced with identical anodizing parameters but in an anodizing bath at different stages of bath aging or the time of use, respectively. The bath aging was monitored by the conductivity and was related to the consumed charge. The oxide layers were characterized by scanning electron microscopy (SEM)/electron dispersive x‐ray spectroscopy (EDX) and X‐ray fluorescence analysis. The corrosion behavior was characterized by a combination of electrochemical measurements (linear sweep voltammetry and electrochemical impedance spectroscopy) and corrosion tests (droplet and salt spray tests). It is shown in this paper that the kinetics of oxide formation, as well as the oxide composition, changes with ongoing bath aging. The corrosion protection of the anodic layers strictly depends on the time of use of the anodizing bath and decreases continuously with ongoing bath aging.

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In Situ and Operando AFM and EIS Studies of Anodization of Al 6060: Influence of Intermetallic Particles

Cited by 55 publications

References 49 publications

First-Principle Calculation of Volta Potential of Intermetallic Particles in Aluminum Alloys and Practical Implications

First-Principle Calculation of Volta Potential of Intermetallic Particles in Aluminum Alloys and Practical Implications

Volta Potential Evolution of Intermetallics in Aluminum Alloy Microstructure Under Thin Aqueous Adlayers: A combined DFT and Experimental Study

Corrosion behavior of anodized AA‐6060 depending on the anodizing bath aging

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