Research advances in magnesium and magnesium alloys worldwide in 2020

Improving the wear resistance of plasma electrolytic oxidation (PEO) coatings applied on Mg and its alloys under the addition of nano- and micro-sized additives into the electrolytes: A review

Flash-PEO as an alternative to chromate conversion coatings for corrosion protection of Mg alloy

Sealing of PEO coated AZ91magnesium alloy using solutions containing neodymium

Effect of carbonate additive on the microstructure and corrosion resistance of plasma electrolytic oxidation coating on Mg-9Li-3Al alloy

Plasma Electrolytic Oxidation coatings (PEO), without and with Ce-based sealings, were developed on a Mg–Y–Zn alloy containing long period stacking order (LPSO) phases in order to improve its corrosion behaviour. Specimens were investigated in terms of morphology, composition and corrosion behaviour (polarization and hydrogen evolution measurements). PEO improved the corrosion resistance compared to the bulk material. Sealing for 5 min plugged the coating pores and cracks with Ce-rich compounds, resulting in improved long-term corrosion behaviour. Sealing for 1 h resulted in excessive dissolution of the coating and deterioration of the inner barrier layer.

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

This study demonstrates a significant improvement of the corrosion resistance of an AZ31B magnesium alloy achieved by the application of 1 μm-thin coatings generated by an environmentally friendly flash plasma electrolytic oxidation (FPEO) process in Ca-containing electrolytes. Two compounds with different solubility, calcium oxide (CaO) or calcium glycerophosphate (CaGlyP), were used as sources of Ca in the electrolyte. Very short durations (20–45 s) of the FPEO process were employed with the aim of limiting the energy consumption. The corrosion performance of the developed coatings was compared with that of a commercial conversion coating (CC) of similar thickness. The viability of the coatings in a full system protection approach, consisting of FPEO combined with an inhibitor-free epoxy primer, was verified in neutral salt spray and paint adhesion tests. The superior corrosion performance of the FPEO_CaGlyP coating, both as a stand-alone coating and as a full system, was attributed to the formation of a greater complexity of Ca2+ bonds with SiO2 and PO43− species within the MgO ceramic network during the in situ incorporation of Ca into the coating from a double chelated electrolyte and the resultant difficulties with the hydrolysis of such a network. The deterioration of the FPEO_CaGlyP coating during immersion was found over ten times slower compared with Ca-free flash-PEO coating.

https://www.mdpi.com/2075-4701/10/7/916/pdf

Calcium Doped Flash-PEO Coatings for Corrosion Protection of Mg Alloy

Plasma electrolytic oxidation (PEO) coatings on AZ91 Mg alloy were sealed in calcium nitrate solutions at different pH values (3, 4 and 5). Sodium dodecyl sulfate (SDS) was added to study the effect of SDS on the corrosion resistance of the sealed coatings. The microstructure, chemical composition and corrosion resistance of the coatings were investigated by means of SEM, XPS, XRD and electrochemical corrosion tests. The corrosion performance of the coatings was improved due to precipitation of Ca-containing precipitate. Low pH and SDS addition enhanced hydroxyapatite precipitation and produced hydrophobic coatings with worse paint adhesion but better corrosion resistance.

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

/pdf/ldh-conversion-films-for-active-protection-of-az31-mg-alloy-1otqgfq9.pdf

Borja Pillado

Papers

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

Calcium Doped Flash-PEO Coatings for Corrosion Protection of Mg Alloy

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

LDH conversion films for active protection of AZ31 Mg alloy