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Effect of microstructure on the zinc phosphate conversion coatings on magnesium alloy AZ91

机译：微观结构对AZ91镁合金磷酸锌转化膜的影响

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摘要

The effect of the microstructure, particularly of β-Mg_(17)Al_(12) phase, on the formation and growth of zinc phosphate conversion coatings on magnesium alloy AZ91 (AZ91) was studied. The zinc phosphate coatings were formed on AZ91 with different microstructures produced by heat treatment. The effect of the microstructure on the zinc phosphate coatings were examined using optical microscope (OM), X-ray diffraction (XRD), coatings weight and etching weight balances, scanning electron microscopy (SEM) and salt immersion test. Results showed that as-cast AZ91 contained a high volume fraction of the β-Mg_(17)Al_(12) phase and it was dissolved into α-Mg phase during heat treatment at 400℃. The β-phase became center for hydrogen evolution during phosphating reaction (cathodic sites). The decreased volume fraction of the p-phase caused decreasing both coatings weight and etching weight of the phosphating process. However, it increased the crystal size of the coatings and improved corrosion resistance of AZ91 by immersing in 0.5 M NaCl solution. Results also showed that the structure of the zinc phosphate conversion on AZ91 consisted of two layers: an outer crystal Zn_3(PO_4)_2·4H_2O (hopeite) and an inner which was mainly composed of MgZn_2(PO_4)_2 and Mg_3(PO_4)_2. A mechanism for the formation of two layers of the coatings was also proposed in this study.
机译：研究了微结构，特别是β-Mg_（17）Al_（12）相对镁合金AZ91（AZ91）上磷酸锌转化膜的形成和生长的影响。在AZ91上形成具有通过热处理产生的不同微观结构的磷酸锌涂层。使用光学显微镜（OM），X射线衍射（XRD），涂层重量和蚀刻重量平衡，扫描电子显微镜（SEM）和盐浸试验检查了微观结构对磷酸锌涂层的影响。结果表明，铸态AZ91含有大量的β-Mg_（17）Al_（12）相，并在400℃的热处理过程中溶解为α-Mg相。 β相成为磷化反应过程中氢析出的中心（阴极位）。 p相体积分数的减少导致磷化工艺的涂层重量和蚀刻重量的降低。但是，通过浸入0.5 M NaCl溶液中，它增加了涂层的晶体尺寸并改善了AZ91的耐腐蚀性。结果还表明，AZ91上磷酸锌的转化结构由两层组成：外层晶体Zn_3（PO_4）_2·4H_2O（陨铁）和内层主要由MgZn_2（PO_4）_2和Mg_3（PO_4）_2组成。在这项研究中还提出了形成两层涂层的机理。

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  • 来源
    《Applied Surface Science》 |2013年第1期|70-78|共9页
  • 作者

    Nguyen Van Phuong; Sungmo Moon; Doyon Chang; Kyu Hwan Lee;

  • 作者单位

    Surface Technology Division, Korea Institute of Materials Science, 797 Changwondaero, Seongsan-gu, Changwon, Gyeongnam, 642-831, Republic of Korea,University of Science and Technology, 217 Gajeong-ro, Yuseong-gu, Daejeon, 305-350, Republic of Korea;

    Surface Technology Division, Korea Institute of Materials Science, 797 Changwondaero, Seongsan-gu, Changwon, Gyeongnam, 642-831, Republic of Korea;

    Surface Technology Division, Korea Institute of Materials Science, 797 Changwondaero, Seongsan-gu, Changwon, Gyeongnam, 642-831, Republic of Korea;

    Surface Technology Division, Korea Institute of Materials Science, 797 Changwondaero, Seongsan-gu, Changwon, Gyeongnam, 642-831, Republic of Korea,University of Science and Technology, 217 Gajeong-ro, Yuseong-gu, Daejeon, 305-350, Republic of Korea;

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  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

    magnesium; conversion coating; heat treatment; zinc phosphate; hopeite;

    机译：镁;转化膜;热处理;磷酸锌希望者;

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