Ca、Y改性的Mg-2Zn-1Al镁合金腐蚀行为

Corrosion Behavior of Ca and Y Micro-alloyed Mg-2Zn-1Al Alloy

摘要:

采用扫描电镜、XRD、析氢及电化学测试等对0.2%Ca、0.2%Y改性的Mg-2Zn-1Al （ZA21）轧制板材的微观组织和腐蚀行为进行了分析。结果表明，Ca和Y细化了晶粒，改变了第二相类型，降低了含Mn相中锰含量。在3.5%NaCl溶液中，优先腐蚀位点位于含Mn相附近的镁基体上，12 h腐蚀速率满足：ZA21 (8.59 mm/a)>ZA21+0.2%Ca (7.17 mm/a)>ZA21+0.2%Y (4.22 mm/a)>ZA21+0.2%Ca+0.2%Y (1.26 mm/a)。耐蚀性提升可归因于晶粒的细化；高Mn相消失，低Mn相和无Mn相生成导致微电偶腐蚀减弱；Mg、 Mg(OH)₂、Ca₃Al₂O₆·xH₂O、CaY₄O₇和Y₂O₃组成的更致密、裂纹更浅、保护性更强的腐蚀产物膜替代了由Mg和Mg(OH)₂组成的充满裂纹、保护作用有限的腐蚀产物膜。

Abstract:

Microstructure and corrosion behavior of 0.2wt% Ca and/or 0.2wt% Y modified Mg-2Zn-1Al (ZA21) rolled sheets were analyzed by SEM, XRD, hydrogen evolution and electrochemical measurement. Results show that Ca and Y refine the grains, modify the second phases, and reduce the Mn content in Mn-containing phase. In 3.5wt% NaCl solution, the preferential corrosion sites locate at the Mg-matrix near Mn-containing phases. The 12 h-corrosion rates satisfy ZA21 (8.59 mm/a)>ZA21+0.2Ca (7.17 mm/a)>ZA21+0.2Y (4.22 mm/a)>ZA21+0.2Ca+0.2Y (1.26 mm/a). The enhanced corrosion resistance of the Ca, Y modified alloys can be accredited to the follows: (1) the refinement of grain size; (2) the devitalization of the intensity of the micro-galvanic corrosion by generating low-Mn and non-Mn phases rather than the high Mn-content phases; (3) the dense, shallower cracked and more protective corrosion product film composed of Mg, Mg(OH)₂, Al₂O₃, Ca-containing and Y-containing components replaces the fully-cracked and limited protective one without Ca, Y incorperation.