Corrosion mechanism of a MgF2 film on AZ31 magnesium alloy: A cyclic process of localized dissolution and metastable product plugging.
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| Title: | Corrosion mechanism of a MgF2 film on AZ31 magnesium alloy: A cyclic process of localized dissolution and metastable product plugging. |
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| Authors: | Wu, Li-Ping1 (AUTHOR) wuliping2008@126.com, Yang, Y.Z.2 (AUTHOR), Zhang, Y.2 (AUTHOR) |
| Source: | Applied Surface Science. Nov2026, Vol. 745, pN.PAG-N.PAG. 1p. |
| Subjects: | Magnesium fluoride, Pitting corrosion, Magnesium alloys, Corrosion inhibitors, Magnesium hydroxide, Corrosion engineering, Salt, Corrosion & anti-corrosives |
| Abstract: | [Display omitted] • The debate on the corrosion of MgF 2 film in chloride media was resolved. • Corrosion mechanism was governed by cyclic localized dissolution and plugging. • Metastable Mg 3 (OH) 5 Cl·4H 2 O phase formed within the pits, temporarily enhancing resistance. • MgF 2 dissolved while Mg(OH) 2 remained stable during attack. • Final failure of the MgF 2 film was due to P5 decomposition and spallation. The degradation mechanism of MgF 2 films on magnesium (Mg) alloys in chloride environments remains contentious, with debate centering on whether MgF 2 dissolves or remains stable. This study elucidated the corrosion pathway of a well–defined MgF 2 film potentiostatically deposited on AZ31 Mg alloy in a 3.5 wt% NaCl solution. Contrary to some views, the film, which is composed of crystalline MgF 2 and amorphous Mg(OH) 2 , did not fail uniformly nor did MgF 2 directly convert to MgCl 2. Instead, failure initiated via localized pitting at defects, where MgF 2 progressively dissolved, releasing Mg2+ and F– ions, while Mg(OH) 2 underwent net precipitation and persisted in the corrosion product layer. The released Mg2+ precipitated with Cl– and OH– to form metastable Mg 3 (OH) 5 Cl·4H 2 O (P5 phase) and Mg(OH) 2 within the pits, temporarily plugging them and enhancing corrosion resistance. Ultimate failure occurred as the P5 phase decomposed and spalled off, re–exposing the substrate and accelerating corrosion. This work clarified the degradation pathway by revealing a cyclic process of localized dissolution and temporary plugging, thereby reconciling the conflicting views in the literature. [ABSTRACT FROM AUTHOR] |
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| Database: | Engineering Source |
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