Corrosion of Cast Aluminum Alloys under Heat-Transfer Conditions

Wiggle, R. R.; Hospadaruk, V.; Tibaudo, F. M.

doi:10.4271/810038

Cited by 23 publications

(9 citation statements)

References 5 publications

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“…The pitting process involves a series of reaction steps including the adsorption of the C1-anion and its chemical interaction with the passive film and subsequent thinning of the film followed by the exposure and rapid dissolution of the metal substrate (4). The overall process can be effectively controlled in aluminum through the use of inhibitors, such as either molybdates, chromates, or nitrates (5,6), in the solution. The mechanism by which the corrosion inhibitor improves the integrity of the passive film is not clearly understood.…”

mentioning

confidence: 99%

Corrosion Behavior of Aluminum‐Molybdenum Alloys in Chloride Solutions

Moshier¹,

Davis²,

Ahearn³

et al. 1987

J. Electrochem. Soc.

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The electrochemical response of Al alloys containing various concentrations of Mo in solid solution was studied using potentiodynamic polarization. The evolution of the chemical composition of the passive film during exposure to deaerated 0.1N normalKCl was analyzed using x‐ray photoelectron spectroscopy. Exposure of Al‐Mo alloys to the chloride solution results in an increase in the corrosion potential and a decrease in the cathodic Tafel slope. The breakdown potential is also found to increase with higher concentrations of Mo in the alloy. These results correlate with an increase in the amount of Mo in the oxide film during polarization, even though the concentration of Mo in the passive film is well below that in the alloy. This work suggests that the oxidized Mo in the passive film inhibits the nucleation of pits in the alloy by improving the integrity of the passive film.

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mentioning

confidence: 99%

Corrosion Behavior of Aluminum‐Molybdenum Alloys in Chloride Solutions

Moshier¹,

Davis²,

Ahearn³

et al. 1987

J. Electrochem. Soc.

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“…Eb is rather nonreproducible in an inhibited environment, while in a noninhibited or slightly aggressive medium where the metals do not passivate, it is quite reproducible. The single critical potential, Epp, proposed by Broli et al (4) and the Epit obtained by Wiggle et al (10) (both obtained by icontrolled methods) probably correspond to Eb. In media such as chloride or nitrate, both of these potentials would be equivalent to Eprot; however, in highly inhibited medium, e.g., experimental coolant No.…”

Section: Resultsmentioning

confidence: 79%

Galvanostaircase Polarization

Hirozawa

1983

J. Electrochem. Soc.

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polarization behavior of the anodic and cathodic reactions. Rather, the effect was of a chemical nature, and AV caused a profound change in the mechanism of iron dissolution and film formation processes in chlorate solution. It is suggested that further studies be undertaken to resolve the problem. ConclusionsA study has been made of the effect of alternating voltage (AV) on the polarization of mild steel in neutral sodium sulfate, nitrate, perchlorate, and chlorate solutions. The types of AV used were 60 Hz sinusoidal, square, and triangular waves, and the measurements were carried out for a range of AV from O to 2000 mV rms. Based upon the experimental results, the following conclusions could be made:1. AV caused a shift in the corrosion potential toward the negative direction for mild steel in sulfate, nitrate, and perchlorate solutions. In chlorate solution, the corrosion potential was shifted toward the positive direction.2. AV behaved as a depolarizer and substantially increased d-c current densities in the active and the transpassive regions of the polarization curves.3. In the passive region, AV destroyed the passivity and increased the passivity current density by one to two orders of magnitude for mild steel in sulfate, nitrate, and perchlorate solutions. In chlorate solution, AV prevented the formation of oxide film on the electrode, and completely eliminated the passive region in the polarization measurements.4. At high AV values, two distinct active-to-passive transitional potentials were observed for mild steel in nitrate and perchlorate solutions.5. The effects of various AV waveforms were qualitatively similar for all the solutions investigated. Triangular wave caused the severest destruction of pas-sivity in the passive region; whereas square wave caused the highest increase in d-c current in the active and the transpassive regions.6. A simple mathematical model was used for the computer simulation of the polarization behavior of the mild steel electrode under the superimposed AV conditions. The simulated curves agreed qualitatively with the experimental curves for sulfate, nitrate, and perchlorate solutions.

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“…Wiggle et al [2] studied the effect of molybdates on the pitting behavior of two aluminum alloys, AA3003 and AA7072, in ethylene glycol/water/molybdate mixtures and found that E b becomes more noble, increasing monotonically with the concentration of molybdate anions in the solution. Stranick [3] found that molybdates increase E b for AA 300 in hard water containing 250 ppm Cl ) under neutral and alkaline conditions.…”

Section: Introductionmentioning

confidence: 98%

“…The interaction of molybdates with Al and their impact on the corrosion resistance of Al have been the subject of several papers [2][3][4][5][6][7][8]. Wiggle et al [2] studied the effect of molybdates on the pitting behavior of two aluminum alloys, AA3003 and AA7072, in ethylene glycol/water/molybdate mixtures and found that E b becomes more noble, increasing monotonically with the concentration of molybdate anions in the solution.…”

Section: Introductionmentioning

confidence: 99%

Corrosion protection of AA6061 T6-10 % Al2O3 composite by molybdate conversion coatings

2005

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The corrosion protection performance of aluminum composite materials was investigated in 3.5% NaCl solution for time ranging between 1-60 days. Series of specimens were treated in molybdate solutions under different conditions. Free immersion and electrochemical activation techniques were used to apply the molybdate layer. The specimens which were directly treated or pickled before molybdate treatment showed severe pitting corrosion. Conversely, the specimens which were subjected to an oxide thickening step before the molybdate treatment showed outstanding corrosion protection. XPS revealed a higher amount of molybdate as MoO 42) for the specimens prepared by electrochemical activation technique than for the free immersion technique.

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Corrosion of Cast Aluminum Alloys under Heat-Transfer Conditions

Cited by 23 publications

References 5 publications

Corrosion Behavior of Aluminum‐Molybdenum Alloys in Chloride Solutions

Corrosion Behavior of Aluminum‐Molybdenum Alloys in Chloride Solutions

Galvanostaircase Polarization

Corrosion protection of AA6061 T6-10 % Al2O3 composite by molybdate conversion coatings

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