稀土对AZ91镁合金干湿交替循环腐蚀行为的影响

Effect of Misch Metal on the Corrosion Behavior of AZ91 Magnesium Alloys under Wet-Dry Cycles

镧铈(La,Ce)混合稀土的添加改变了AZ91镁合金微观组织和元素分布。La元素与Ce元素在AZ91镁合金中以不同的形式存在,一部分固溶在镁合金基体中,一部分参与生成了针状的Al4(La,Ce)相和粒状的Al_(10)Ce_2Mn_7相。稀土添加后AZ91镁合金中β相的体积分数有所降低,Al元素分布由晶界向晶内迁移。对不同添加量的稀土镁合金在模拟融雪剂溶液中的干湿交替循环腐蚀行为的研究结果表明,La、Ce混合稀土的添加,可以增加镁合金表面膜的致密度。虽然混合稀土降低了镁合金的自腐蚀电位,但腐蚀电流密度相比较于AZ91明显降低。SECM结果则表明,稀土添加可以减少镁合金表面微区的活性点数量。

The microstructure and element distribution of AZ91 alloy were changed by adding the mischmetal of lanthanum and cerium（La, Ce）. La or Ce element can be found in various phases of AZ91 alloy with mischmetal addition. Part of them can be dissolved in the α-Mg solid solution, while the others formed different intermetallic compounds with chemical composition Al4（La,Ce） or Al_（10）Ce_2Mn_7. Al_4（La,Ce） is in acicular shape and Al_（10）Ce_2Mn_7 is in granular shape. The fraction of β phase in AZ91 alloy decreased obviously with the addition of mischmetal, and the distribution of Al element transferred from the grain boundaries to grain internal area. The results of the corrosion behavior of AZ91 magnesium alloys with addition of mischmetal in snow-melt agent solution under wet-dry cycles show that a shift of the corrosion potential（Ecorr） towards more negative values is observed for all the alloys with mischmetal addition, but their corrosion current densities（Icorr） are much lower than that of the AZ91 alloy. The scanning electrochemical microscopy（SECM） test results reveal that the addition of mischmetal could reduce the number of electrochemical active points on the surface. In addition, the compactness of corrosion product film of magnesium alloy is increased with addition of mischmetal.