The Difference Effect and the Chunk Effect

Marsh, G. A.; Schaschl, E.

doi:10.1149/1.2427579

Cited by 70 publications

(42 citation statements)

References 6 publications

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“…The chunk breakage in magnesium alloy has been frequently reported in previous studies [7,17], but its evidence is still unclear. In the present study, the chunk breakage of a precipitate was accidentally detected on the observation of corrosion products after an immersion test.…”

Section: Effect Of Solute Segregation and Chunk Breakagementioning

confidence: 97%

“…The main stream of this research is divided into four categories: the effect of heavy metal impurity (Fe, Cu, Ni) [1][2][3], precipitate [4], surface structure and chemistry [5,6], and electrochemical properties [7,8]. First, the effect of heavy metal impurity (Fe, Cu, Ni) on the corrosion properties of Mg alloys was investigated very extensively and profoundly by J. D. Hanawalt, et al, 1942 [1].…”

Section: Introductionmentioning

confidence: 99%

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Effect of galvanic corrosion between precipitate and matrix on corrosion behavior of As-cast magnesium-aluminum alloys

Lee¹,

Kang

Shin

2000

Metals and Materials

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In the present study, the corrosion behavior of an as-cast magnesium alloy was studies focusing on the galvanic corrosion between a precipitate and Mg-rich matrix. Through immersion and electrochemical tests, the variation of the corrosion behavior with the alloy composition and alloy system was discussed in detail. The corrosion rate of an as-cast alloy increased abruptly to 9 wt.% A1 in both alloys, but in the composition range of over 12 wt.% A1, the corrosion rate reveals a different tendency than the alloy system. The [~-phase that is a typical precipitate in an Mg-xA1 alloy is a more potent cathodic phase than is the ternary precipitate in a Mg-xAl1Zn alloy. In the case of the Mg-xA1 alloy, the formation of a galvanic cell between the precipitate and matrix promotes the preferred dissolution of the matrix, but the precipitate in the Mg-xAl-lZn alloy has a minor effect on the corrosion behavior of the Mg-rich matrix. However, the corrosion rate of as-cast MgxA1 and Mg-xAl-lZn alloys which contain precipitate, depends mainly upon the corrosion behavior of the Mg-rich matrix, which is influenced by the A1 content. It depends additionally upon the variation of the Anode-Cathode Area Ratio (ACAR) and the chunk breakage of precipitate during corrosion.

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Section: Effect Of Solute Segregation and Chunk Breakagementioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

Effect of galvanic corrosion between precipitate and matrix on corrosion behavior of As-cast magnesium-aluminum alloys

Lee¹,

Kang

Shin

2000

Metals and Materials

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“…The corrosion property of Mg alloys depends mainly upon the effect of heavy metal impurity [1-3], precipitate [4], surface chemistry [5,6], and electrochemical property [7,8]. J.D.…”

Section: Introductionmentioning

confidence: 99%

Effect of an Mg-rich matrix on the corrosion behavior of As-cast magnesium-aluminum alloys

Lee¹,

Kang

Shin

2000

Metals and Materials

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In the present study, the corrosion behavior of as-cast Mg-AI and Mg-AI-Zn alloys was studied as a function of the A1 content in the matrix. Corrosion properties such as the corrosion rate, corrosion potential, and repassivation tendency were estimated through immersion and electrochemical tests. The corrosion potential and corrosion rate of a solutionized alloy depend mainly on the A1 content of the as-cast alloy. The variation of A1 content in the Mg-rich matrix influences the stability of the passive film and the repassivation tendency, i.e., as the A1 content of the matrix increases, the repassivation tendency of the surface protective film after its breakage deteriorates. Also, it was proven that the enhancement of corrosion resistance by heat treatment, as in T6, is due to the decrease of solute concentration in the matrix, in addition to the effect of the precipitate, which plays the role of a barrier against corrosion.

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“…When the experiment was repeated with the aluminum connected to a more noble metal immersed in the same solution, the total rate of hydrogen evolution l'; was found to be greater than VI ' They reasoned that "when a metal is made an anode in an electrolytic cell, its rate of corrosion should be the sum of (a) local action as observed in the absence of external current," i.e., VI' "and (b) the corrosion rate equivalent to the applied current," i.e., V 3 , "(utilizing the electrochemical equivalent of the metal in question)." 30 Contrary to this result, they found that their measured corrosion rate was actually different from the sum of (a) and (b).…”

Section: Difference Effectmentioning

confidence: 74%

Anodic Dissolution of Metals—Anomalous Valence

James

1974

Advances in Corrosion Science and Technology

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INTRODUCTIONWhen metals are dissolved anodically in aqueous and nonaqueous media, the weight of metal dissolved is sometimes greater than that calculated from Faraday's law assuming normal oxidation states. Among several metals of industrial importance, AI, Be, Cd, Fe, Pb, Mg, Ti, and Zn exhibit this phenomenon. The usual implication is that these metals dissolve as ions with an ionic valence or oxidation number less than normal, e.g., Mg+, Be+, etc.Actually, anomalous anodic dissolution, i.e., that which results in a weight loss of an anode larger than that based on coulometric data, was first reported for Al over a century ago by its discoverers, Wohler and Buff. 1 Yet interestingly enough, despite the considerable research which has focused on this problem since that time, the exact nature of anomalous dissolution of metals remains in dispute.One mechanism which has received considerable support is the concept of univalent (unipositive) ion formation, sometimes referred to as the transitory ion mechanism.The unipositive (uncommon) ion mechanism has been especially espoused in large part by two major groups: Epelboin and co-workers at the University of Paris and Davidson, Kleinberg, and co-workers at the University of Kansas, Lawrence. The mechanism was first employed by Epelboin to explain the apparent valence of 1.40 for Zn dissolving anodically in aqueous perchlorate solution. 2 This value was obtained both from Straumanis, James, and co-workers at the University of MissouriRolla have attributed anomalous anodic dissolution of metals in aqueous solution, as have many other electrochemists, to the competition of secondary processes with an electrochemical oxidation step excluding that of transitory ion formation. They have explained the anomalous dissolution of many metals in aqueous media as arising from related phenomena: local action, film-controlled polarization, and anodic disintegration. The reader should be made aware that these phenomena often involve, but are not necessarily confined to, secondary processes frequently encountered in the electrochemistry of metals dissolving in dilute aqueous systems. Indeed, the major complaint of Epelboin is that too many electrochemists choose to confine their studies of anomalous anodic dissolution within the framework of classical electrochemistry. Despite the conflicting philosophies of the different approaches, considerable credit must be accorded to Epelboin and his colleagues in their extensive and well-planned efforts to come up with a universal and quantitative mechanism of anodic dissolution based on sound kinetic and thermodynamic principles.There is no argument that experimental and theoretical considerations of anomalous dissolution from existing and new points of view are essential to research and development with regard to corrosion protection and inhibition, batteries and other energy devices, electrochemical synthesis, and other associated electronic properties of interfaces. Accordingly, the following review is presented with the hope that it will ...

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The Difference Effect and the Chunk Effect

Cited by 70 publications

References 6 publications

Effect of galvanic corrosion between precipitate and matrix on corrosion behavior of As-cast magnesium-aluminum alloys

Effect of galvanic corrosion between precipitate and matrix on corrosion behavior of As-cast magnesium-aluminum alloys

Effect of an Mg-rich matrix on the corrosion behavior of As-cast magnesium-aluminum alloys

Anodic Dissolution of Metals—Anomalous Valence

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