PEO coating with Ce-sealing for corrosion protection of LPSO Mg–Y–Zn alloy

Mohedano, Marta; Pérez, P.; Matykina, E.; Pillado, Borja; Garcés, G.; Arrabal, R.

doi:10.1016/j.surfcoat.2019.125253

Cited by 34 publications

(15 citation statements)

References 53 publications

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“…The deposition of rare earth and molybdenum compounds is another effective and low-cost approach to block the pores and other defects in the anodic films. Chemical conversion treatments by immersion in aqueous solutions containing salts such as Na 3 PO 4 [ 264 ], Ca(NO 3 ) 2 [ 279 ], (Ce(NO 3 ) 3 [ 280 , 281 ], La(NO 3 ) 3 [ 278 ], Na 2 SnO 3 [ 282 ], NaNd(SO 4 ) 2 [ 283 ], or Na 2 MoO 4 [ 284 ] rely on the redox reactions that take place on the surface, producing compounds such as Ca 10 (PO 4 ) 6 (OH) 2 [ 279 ], La(OH) 3 [ 278 ], CeO 2 /Ce 2 O 3 [ 280 ], MgSnO 3 [ 282 ], Nd 2 O 3 [ 283 ], and MoO 3 [ 284 ]. An advantage of the process is that high temperature curing is not needed after sealing.…”

Section: Post-treatmentmentioning

confidence: 99%

Chromate-Free Corrosion Protection Strategies for Magnesium Alloys—A Review: Part II—PEO and Anodizing

et al. 2022

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Although hexavalent chromium-based protection systems are effective and their long-term performance is well understood, they can no longer be used due to their proven Cr(VI) toxicity and carcinogenic effect. The search for alternative protection technologies for Mg alloys has been going on for at least a couple of decades. However, surface treatment systems with equivalent efficacies to that of Cr(VI)-based ones have only begun to emerge much more recently. It is still proving challenging to find sufficiently protective replacements for Cr(VI) that do not give rise to safety concerns related to corrosion, especially in terms of fulfilling the requirements of the transportation industry. Additionally, in overcoming these obstacles, the advantages of newly introduced technologies have to include not only health safety but also need to be balanced against their added cost, as well as being environmentally friendly and simple to implement and maintain. Anodizing, especially when carried out above the breakdown potential (technology known as Plasma Electrolytic Oxidation (PEO)) is an electrochemical oxidation process which has been recognized as one of the most effective methods to significantly improve the corrosion resistance of Mg and its alloys by forming a protective ceramic-like layer on their surface that isolates the base material from aggressive environmental agents. Part II of this review summarizes developments in and future outlooks for Mg anodizing, including traditional chromium-based processes and newly developed chromium-free alternatives, such as PEO technology and the use of organic electrolytes. This work provides an overview of processing parameters such as electrolyte composition and additives, voltage/current regimes, and post-treatment sealing strategies that influence the corrosion performance of the coatings. This large variability of the fabrication conditions makes it possible to obtain Cr-free products that meet the industrial requirements for performance, as expected from traditional Cr-based technologies.

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Section: Post-treatmentmentioning

confidence: 99%

Chromate-Free Corrosion Protection Strategies for Magnesium Alloys—A Review: Part II—PEO and Anodizing

et al. 2022

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“…Sealing of the pores can be achieved via different surface post-treatments that are described in detail in PART II of this review [ 9 ]. Some chemicals known for their inhibition effect on Mg alloys, such as rare earth element salts [ 240 , 241 , 242 , 243 , 244 , 245 , 246 , 247 , 248 , 249 ], phosphates [ 242 , 250 ], stannate [ 240 ], and surfactants [ 240 ], can be used primarily for the sealing post-treatment. In such a case, their inhibition effect on the Mg substrate also contributes to a reduction in the corrosion rate and provides active inhibition.…”

Section: Combining Inhibitors With Other Corrosion Protection Strategiesmentioning

confidence: 99%

Chromate-Free Corrosion Protection Strategies for Magnesium Alloys—A Review: Part III—Corrosion Inhibitors and Combining Them with Other Protection Strategies

et al. 2022

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Owing to the unique active corrosion protection characteristic of hexavalent chromium-based systems, they have been projected to be highly effective solutions against the corrosion of many engineering metals. However, hexavalent chromium, rendered a highly toxic and carcinogenic substance, is being phased out of industrial applications. Thus, over the past few years, extensive and concerted efforts have been made to develop environmentally friendly alternative technologies with comparable or better corrosion protection performance to that of hexavalent chromium-based technologies. The introduction of corrosion inhibitors to a coating system on magnesium surface is a cost-effective approach not only for improving the overall corrosion protection performance, but also for imparting active inhibition during the service life of the magnesium part. Therefore, in an attempt to resemble the unique active corrosion protection characteristic of the hexavalent chromium-based systems, the incorporation of inhibitors to barrier coatings on magnesium alloys has been extensively investigated. In Part III of the Review, several types of corrosion inhibitors for magnesium and its alloys are reviewed. A discussion of the state-of-the-art inhibitor systems, such as iron-binding inhibitors and inhibitor mixtures, is presented, and perspective directions of research are outlined, including in silico or computational screening of corrosion inhibitors. Finally, the combination of corrosion inhibitors with other corrosion protection strategies is reviewed. Several reported highly protective coatings with active inhibition capabilities stemming from the on-demand activation of incorporated inhibitors can be considered a promising replacement for hexavalent chromium-based technologies, as long as their deployment is adequately addressed.

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“…Sealing of the porous layer by post-treatment has been explored as an alternative to improve the long-term corrosion resistance of PEO coated Mg alloy. Sol-gel [12][13][14], epoxy [15][16][17][18] and inorganic coatings [19][20][21][22][23] are examples of strategies aimed at forming additional layers or blocking the coating pores and defects. As a general rule, when compared with organic sealings, inorganic based post-treatments are easier to apply, more environmentally friendly and show better thermal and mechanical integrity [24].…”

Section: Introductionmentioning

confidence: 99%

“…It was recently found that optimized Ce-based treatment can improve the corrosion performance of PEO coatings by sealing the open pores with precipitation product. However, the acidic electrolyte used during post-treatment process may lead to excessive coating dissolution and deterioration of the inner barrier layer [19,20,22]. Mingo et al [27] investigated the sealing effect of three different post-treatment processes on the corrosion property of PEO coatings on AZ91 Mg alloy.…”

Section: Introductionmentioning

confidence: 99%

Ca-based sealing of plasma electrolytic oxidation coatings on AZ91 Mg alloy

Mohedano

et al. 2021

Surface and Coatings Technology

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PEO coating with Ce-sealing for corrosion protection of LPSO Mg–Y–Zn alloy

Cited by 34 publications

References 53 publications

Chromate-Free Corrosion Protection Strategies for Magnesium Alloys—A Review: Part II—PEO and Anodizing

Chromate-Free Corrosion Protection Strategies for Magnesium Alloys—A Review: Part II—PEO and Anodizing

Chromate-Free Corrosion Protection Strategies for Magnesium Alloys—A Review: Part III—Corrosion Inhibitors and Combining Them with Other Protection Strategies

Ca-based sealing of plasma electrolytic oxidation coatings on AZ91 Mg alloy

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