Formation behavior of phosphoric acid-based chemical conversion coating containing alkaline earth metals on magnesium alloy

Akinori Nakamura, Satoshi Oue, Hiroki Koga, Hiroaki Nakano

    Research output: Contribution to journalArticlepeer-review

    Abstract

    The phosphate coating for Mg alloy was performed in the unagitated solutions containing 1 g·dm-3 of Mg, Ca, Sr and Ba as alkali-earth metal and 50 g·dm-3 of H3PO4 of pH 3 and 40°C for 3 min, and the structure and formation behavior of the phosphate films were investigated. The X-ray diffraction patterns of phosphate films broadened regardless of the kinds of alkali-earth metal, which was a characteristic of an amorphous structure. XPS analysis revealed that the valence of P in the phosphate films was pentavalent. The pH in the vicinity of the Mg alloy during the phosphate coating, as measured using an Sb microelectrode, was approximately 10.4, 11.4, 10.7, 12.0 in the solutions containing Mg, Ca, Sr and Ba, respectively, which shows that the phosphoric acid dissociates to the third stage during the phosphate coating and the phosphate films composed of M3(PO4)2 containing alkali-earth metal (M) are formed. The phosphate coating were successively performed in the two kinds of solutions containing different alkali-earth metals and the cross section was analyzed, as a result, it was suggested that the new phosphate films were formed at the interface between Mg alloy substrate and phosphate films and the previously formed phosphate films were boosted up in films.

    Original languageEnglish
    Pages (from-to)684-690
    Number of pages7
    JournalNippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals
    Volume80
    Issue number11
    DOIs
    Publication statusPublished - 2016

    All Science Journal Classification (ASJC) codes

    • Condensed Matter Physics
    • Mechanics of Materials
    • Metals and Alloys
    • Materials Chemistry

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