Effect of Segregation and Surface Condition on Corrosion of Rheo-HPDC Al–Si Alloys

Eslami, Maryam; Payandeh, Mostafa; Deflorian, F.; Jarfors, Anders E. W.; Zanella, Caterina

doi:10.3390/met8040209

Cited by 12 publications

(25 citation statements)

References 62 publications

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“…[68][69][70] and in general more Si on the surface increases the surface resistance values. Our previous study on these two Al-Si alloy confirms this fact 64 .…”

Section: Electrochemical Behaviorsupporting

confidence: 70%

“…The EDXS analysis confirms their presence. As our previous study has shown 64 , the presence of these phases (the eutectic silicon and iron-rich IM particles) together with α-Al garins in the alloy microstructure results in the formation of microgalvanic cells, which make the alloy prone to localized corrosion. relatively large pits are visible.…”

Section: Layer Characterizationmentioning

confidence: 99%

“…A 400 ton high pressure die cast (HPDC) machine was used to produce the component. Details of the casting process are presented elsewhere 64 . Before immersion in the conversion solution, samples were ground using SiC abrasive papers of P1200 and P4000, respectively.…”

Section: Substrate Preparationmentioning

confidence: 99%

“…2(a) and (b). The breakdown of the oxide layer takes place especially at the interface between α-Al phase and the eutectic silicon and/or iron-rich IM particles 64 . This phenomenon can be controversial, since it may also result in the formation of subsurface crevices 24 .…”

Section: Morphology and Compositionmentioning

confidence: 99%

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Deposition and Characterization of Cerium-Based Conversion Coating on HPDC Low Si Content Aluminum Alloy

Eslami¹,

Fedel²,

Speranza³

et al. 2017

J. Electrochem. Soc.

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Cerium-based conversion coatings were deposited on high pressure die cast (HPDC) Al-Si alloys using an immersion method. Hydrogen peroxide and sodium chloride were added to the conversion solution to accelerate the coating formation and to understand its formation mechanism. These studies showed that the deposition of cerium hydroxide/oxide conversion layer starts from iron-rich intermetallic particles, which are located inside the eutectic region and then the coating growth continues to cover the entire alloy surface. This phenomenon passivates the active interfaces between iron-rich intermetallic particles and/or the eutectic silicon phase and the aluminum matrix, which are prone to localized corrosion in chloride ions containing environments. Accordingly, values of the total impedance in EIS measurements significantly increased for the treated substrates. Morphologies of the conversion coatings and the oxidation state of cerium compounds were found to be dependent on the composition of the solution and the presence of chloride ions and/or hydrogen peroxide. Aluminum alloy with higher silicon content showed a more active surface during immersion in the conversion solution. This makes it more difficult to be treated using aggressive conversion solutions.

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“…[68][69][70] and in general more Si on the surface increases the surface resistance values. Our previous study on these two Al-Si alloy confirms this fact 64 .…”

Section: Electrochemical Behaviorsupporting

confidence: 70%

Section: Layer Characterizationmentioning

confidence: 99%

Section: Substrate Preparationmentioning

confidence: 99%

Section: Morphology and Compositionmentioning

confidence: 99%

See 2 more Smart Citations

Deposition and Characterization of Cerium-Based Conversion Coating on HPDC Low Si Content Aluminum Alloy

Eslami¹,

Fedel²,

Speranza³

et al. 2017

J. Electrochem. Soc.

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“…However, the effect of semisolid process on corrosion of aluminum alloys is still controversial. Previous researches 24,25 have shown that the higher amount of eutectic phase on the surface as a result of surface liquid segregation (SLS) in semisolid-HPDC aluminum alloys can increase the pitting susceptibility. Depending on the silicon percentage, Al-Si alloys are categorized into hypoeutectic alloys with 5 to 10 % silicon, eutectic alloys containing 11-13 % silicon, and hypereutectic alloys with a silicon content commonly between 14 and 20 %.…”

Section: Introductionmentioning

confidence: 99%

Electrochemical Behavior of Conventional and Rheo-High-Pressure Die Cast Low Silicon Aluminum Alloys in NaCl Solutions

2019

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The electrochemical behavior of a low silicon aluminum alloy cast by the conventional and rheo-high-pressure die cast processes is evaluated using polarization test and electrochemical impedance spectroscopy in 0.01 M, 0.05 M, 0.1 M, and 0.6 M sodium chloride solutions. Compared to the conventional high-pressure die cast process, rheocasting introduces some alterations in the microstructure including the presence of aluminum grains with different sizes, formed at different solidification stages. According to the results of the anodic polarization test, conventional cast and rheocast samples show similar breakdown potentials. However, the rheocast samples present enhanced oxygen reduction kinetics compared to the conventional cast sample. Based on scanning electron microscopy examinations, localized microgalvanic corrosion is the main corrosion mechanism for both alloys and it initiates at the interface of aluminum with iron-rich intermetallic particles which are located inside the eutectic regions. The corrosion further develops into the eutectic area. Although the rate of the cathodic reaction can be influenced by the semisolid microstructure, according to the results of anodic polarization and electrochemical impedance spectroscopy tests, the corrosion behavior is not meaningfully affected by the casting process.

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Polypyrrole coatings on rheocast aluminum‐silicon alloy: A correlation between properties and electrodeposition conditions

Eslami

Speranza

Deflorian

et al. 2019

Surface & Interface Analysis

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The effect of the electrolyte composition and the deposition potential range on the physical properties and possible corrosion protection effect of polypyrrole coatings on rheocast aluminum-2.5 % silicon alloy is investigated. Solutions with different concentrations of sodium nitrate and an electron transfer mediator reagent were used for the electrodeposition. Polypyrrole coating is able to hinder the entrance of electrolyte. Upon the penetration of chloride ions, the coating can induce passivation of the alloy's surface by its reduction. The thickness of the coating and its ion-barrier properties, controlled by the electrodeposition conditions, are shown as the important factors influencing the protection efficiency. However, localized drastic galvanic coupling at the polypyrrole/aluminum interface forms blisters, causes failure, and limits the possible protection.

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Effect of Segregation and Surface Condition on Corrosion of Rheo-HPDC Al–Si Alloys

Cited by 12 publications

References 62 publications

Deposition and Characterization of Cerium-Based Conversion Coating on HPDC Low Si Content Aluminum Alloy

Deposition and Characterization of Cerium-Based Conversion Coating on HPDC Low Si Content Aluminum Alloy

Electrochemical Behavior of Conventional and Rheo-High-Pressure Die Cast Low Silicon Aluminum Alloys in NaCl Solutions

Polypyrrole coatings on rheocast aluminum‐silicon alloy: A correlation between properties and electrodeposition conditions

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