Corrosion resistance of WE43 and AZ91D magnesium alloys with phosphate PEO coatings

• Published in: Corrosion science Vol. 50; no. 6; pp. 1744 - 1752
• Main Authors: Arrabal, R., Matykina, E., Viejo, F., Skeldon, P., Thompson, G.E.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01-06-2008; Elsevier
• Subjects: A. Magnesium; Applied sciences; B. Polarization; C. Anodic films; C. Oxide coatings; C. Pitting corrosion; Corrosion; Corrosion environments; Exact sciences and technology; Metals. Metallurgy; Production techniques; Surface treatment; A. Magnesium; C. Anodic films; C. Oxide coatings; C. Pitting corrosion; B. Polarization; Phosphates; Corrosion resistance; A. Magnesium;C. Oxide coatings;C. Anodic films;B. Polarization;C. Pitting corrosion; Magnesium base alloys; Pitting corrosion; Coatings
• ISSN: 0010-938X; 1879-0496
• DOI: 10.1016/j.corsci.2008.03.002

The corrosion performance of WE43-T6 and AZ91D magnesium alloys with and without treatment by plasma electrolytic oxidation (PEO) was investigated by electrochemical measurements in 3.5
wt.% NaCl solution. For untreated WE43-T6 alloy, formation of a uniform corrosion layer (Mg(OH)
2) was accompanied by initial pits around magnesium-rare earth intermetallic compounds. The AZ91D alloy disclosed increased corrosion susceptibility, with localized corrosion around the β-phase, though the β-phase network phase acted as a barrier for corrosion progression. PEO treatment in alkaline phosphate electrolyte improved the corrosion resistance of WE43-T6 alloy only at the initial stages of immersion in the test solution. However, PEO-treated AZ91D alloy revealed a relatively high corrosion resistance for much increased immersion times, contrary to the relative corrosion resistances of the untreated alloys. The improved performance of the PEO-treated AZ91D alloy appears to be related to the formation of a more compact coating.