The role of microstructure and cathodic intermetallics in localised deposition mechanism of conversion compounds on Al (Si, Fe, Cu) alloy

Sainis, Salil; Rosoiu, Sabrina; Ghassemali, Ehsan; Zanella, Caterina

doi:10.1016/j.surfcoat.2020.126502

Cited by 12 publications

(17 citation statements)

References 74 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In other words, a cathodic mechanism of protection was observed. This result is in agreement with others obtained in several aluminum alloys, including AA2017 [15,21,38,41].…”

Section: Potentiodynamic Linear Polarization (Lp)supporting

confidence: 93%

See 1 more Smart Citation

Application of Commercial Surface Pretreatments on the Formation of Cerium Conversion Coating (CeCC) over High-Strength Aluminum Alloys 2024-T3 and 7075-T6

Alba-Galvín

González-Rovira

Pedemonte

et al. 2021

Metals

View full text Add to dashboard Cite

The selection of appropriate surface pretreatments is one of the pending issues for the industrial application of cerium-based chemical conversion coatings (CeCC) as an alternative for toxic chromate conversion coating (CrCC). A two-step surface pretreatment based on commercial products has been successfully used here to obtain CeCC on AA2024-T3 and AA7075-T6. Specimens processed for 1 to 15 min in solutions containing CeCl3 and H2O2 have been studied by scanning electron microscopy coupled with energy-dispersive X-ray analysis (SEM-EDX), glow discharge optical emission spectroscopy (GDOES), potentiodynamic linear polarization (LP), electrochemical impedance spectroscopy (EIS), and neutral salt spray (NSS) tests. SEM-EDX showed that CeCC was firstly observed as deposits, followed by a general coverage of the surface with the formation of cracks where the coating was getting thicker. GDOES confirmed an increase of the CeCC thickness as the deposition proceed, the formation of CeCC over 7075 being faster than over 2024. There was a Ce-rich layer in both alloys and an aluminum oxide/hydroxide layer on 7075 between the upper Ce-rich layer and the aluminum matrix. According to LP and EIS, CeCC in all samples offered cathodic protection and comparable degradation in chloride-containing media. Finally, the NSS test corroborated the anti-corrosion properties of the CeCC obtained after the commercial pretreatments employed.

show abstract

“…In other words, a cathodic mechanism of protection was observed. This result is in agreement with others obtained in several aluminum alloys, including AA2017 [15,21,38,41].…”

Section: Potentiodynamic Linear Polarization (Lp)supporting

confidence: 93%

“…However, none of these options has achieved a true industrial application capable of replacing CrCC and the scientific community continues to search for an alternative. Still today, one of the most promising candidates for chromate conversion coating replacement is cerium-based chemical conversion coatings (CeCC) [11,14,[20][21][22].…”

Section: Introductionmentioning

confidence: 99%

Application of Commercial Surface Pretreatments on the Formation of Cerium Conversion Coating (CeCC) over High-Strength Aluminum Alloys 2024-T3 and 7075-T6

Alba-Galvín

González-Rovira

Pedemonte

et al. 2021

Metals

View full text Add to dashboard Cite

show abstract

“…In a similar study, ref. [ 22 ] investigating localized deposit initiation on a mixed microstructure containing Fe-rich IM β as well as Cu-rich IM θ-Al 2 Cu and ω-Al 7 Cu 2 Fe, preferential heavy deposition was seen only on Cu-rich IM upon immersion of the alloy in a solution containing Ce 3+ ions. Even at shorter immersion times of 0.5 h, the whole Cu-rich IM showed a heavy deposit, not just at the boundaries.…”

Section: Resultsmentioning

confidence: 99%

“…The deposition of conversion compound precipitates on Cu-rich IM, in contrast, appeared to cover the whole IM even after short immersion times [ 22 ]. Cu is a good conductor of electricity and thus provides an excellent path to the passage of electrons with a very low electrical resistivity of 1.7× 10 −8 Ωm.…”

Section: Resultsmentioning

confidence: 99%

“…Pardo et al [ 20 ] has observed localized CeCC deposition occurring on β-(Al,Fe,Si) IM and Al–Fe–Si–Mn IM in the cast alloy A361/SiCp composite. Eslami et al [ 21 ] have also observed coating to initiate at the Fe-rich IM in a Al–Si–Fe alloy, but when cast Al–Si alloys contained both Cu and Fe, preferential heavy deposition was seen only on Cu-rich IM as shown in a study by Sainis et al [ 22 ]. Other works [ 23 , 24 , 25 ] have shown varying degrees of surface coverage and the imparted corrosion resistance.…”

Section: Introductionmentioning

confidence: 96%

See 1 more Smart Citation

A Study of the Localized Ceria Coating Deposition on Fe-Rich Intermetallics in an AlSiFe Cast Alloy

Sainis

Zanella

2021

Materials

Self Cite

View full text Add to dashboard Cite

Corrosion inhibiting conversion coating formation is triggered by the activity of micro-galvanic couples in the microstructure and subsequent local increase in pH at cathodic sites, which in the case of aluminium alloys are usually intermetallics. Ceria coatings are formed spontaneously upon immersion of aluminium alloys in a cerium conversion coating solution, the high pH gradient in the vicinity of intermetallics drives the local precipitation of ceria conversion compounds. Cu-rich intermetallics demonstrate a highly cathodic nature and have shown the local precipitation reaction to occur readily. Fe-rich intermetallics are, however, weaker cathodes and have shown varied extents of localized deposits and are in focus in the current work. Model cast Al-7wt.%Si alloys have been designed with 1 wt.% Fe, solidified at different cooling rates to achieve two different microstructures, with big and small intermetallics, respectively. Upon subjecting the two microstructures to the same conversion coating treatment (immersion in a 0.1 M CeCl3 solution) for a short period of 2 h, preferential heavy deposition on the boundaries of the big intermetallics and light deposition on the small intermetallics was observed. Based on these observations, a mechanism of localized coating initiation at these Fe-rich intermetallic particles (IM) is proposed.

show abstract

Selection of appropriate electrochemical deposition regime for cerium conversion coating on anodized AA2024-T3 aircraft alloy

Girginov,

Portolesi,

Kozhukharov

et al. 2024

J Appl Electrochem

View full text Add to dashboard Cite

The role of microstructure and cathodic intermetallics in localised deposition mechanism of conversion compounds on Al (Si, Fe, Cu) alloy

Cited by 12 publications

References 74 publications

Application of Commercial Surface Pretreatments on the Formation of Cerium Conversion Coating (CeCC) over High-Strength Aluminum Alloys 2024-T3 and 7075-T6

Application of Commercial Surface Pretreatments on the Formation of Cerium Conversion Coating (CeCC) over High-Strength Aluminum Alloys 2024-T3 and 7075-T6

A Study of the Localized Ceria Coating Deposition on Fe-Rich Intermetallics in an AlSiFe Cast Alloy

Selection of appropriate electrochemical deposition regime for cerium conversion coating on anodized AA2024-T3 aircraft alloy

Contact Info

Product

Resources

About