| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 1469690 | Corrosion Science | 2011 | 8 Pages |
This investigation studied the crystallization of a chemical conversion layer that formed on AZ91D Mg alloy in carbonic acid. The layer was an amorphous precursor to a crystalline Mg–Al layered double hydrotalcite, which improved the corrosion resistance of the alloy. The precursor must be treated with a strongly alkaline solution, causing the leaching out of amphoteric Al3+. The leaching step evidently caused crystallization from an amorphous precursor layer to a crystalline coating. Nuclear magnetic resonance analysis indicated that Al3+, which was originally randomly coordinated with surrounding OH− in the precursor, coordinated octahedrally with OH− groups in the crystalline conversion coating.
Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► An amorphous precursor layer formed on Mg–Al–Zn alloy in carbonic acid. ► The amorphous layer has high Al3+ concentration. ► Leaching Al3+ out of precursor layer was the first step of crystallization. ► Al3+ leaching only occurred in a strongly alkaline solution. ► The formula of crystalline conversion coating is Mg4.38Zn0.22Al2(OH)13.192CO3·mH2O.
