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含钇AZ91镁合金在连续浸泡与干湿交替环境中的腐蚀行为
发布人：上海艾荔艾金属材料有限公司www.shailiai.com
更新时间：2015-12-31
研究添加不同含量稀土钇(Y)的AZ91镁合金在连续浸泡及干湿交替腐蚀环境中的腐蚀行为。
含钇AZ91镁合金在连续浸泡与干湿交替环境中的腐蚀行为Corrosion behavior of AZ91 magnesium alloys with yttrium under immersion and dry-wet cyclic environments
研究添加不同含量稀土钇(Y)的AZ91镁合金在连续浸泡及干湿交替腐蚀环境中的腐蚀行为。结果表明：添加稀土Y的AZ91镁合金，腐蚀形貌转变为“丝状”腐蚀；在连续浸泡溶液环境中，腐蚀沿着同一条“丝”发展。而在干湿交替腐蚀环境中，腐蚀主要在湿环境下产生和发展，在干环境下停滞。重新置入湿环境时，旧的腐蚀“丝”不会明显发展，而会形成新的腐蚀“丝”，镁合金表面“丝状”腐蚀数量随干湿交替循环腐蚀次数增加而增多。“丝状”腐蚀形貌的形成是由于稀土添加降低了Al元素在晶界上的分布，使得表面析氢腐蚀不易受到阻碍，腐蚀以“腐蚀丝”末端持续析氢向前发展。电化学阻抗测试结果表明：干湿交替腐蚀环境中的电荷转移电阻明显低于连续浸泡环境中对应的电荷转移电阻，这是因为干湿交替过程中，薄液膜的存在延长了镁合金的析氢时间，而干环境的干燥作用破坏了镁合金表面膜的完整性。
The corrosion behavior of AZ91 magnesium alloys with different additions of rare earth yttrium under immersion and dry-wet cyclic environments was studied. The results show that the differences in corrosion morphologies can be found between AZ91 alloy and the alloys with Y additions. The corrosion morphology of the original AZ91 alloy is featured with localized corrosion morphology while the corrosion morphologies of the alloys with Y additions are characterized by filiform corrosion feature. The corrosion extends along the same “line” when the alloys with Y addition are exposed to the immersion environment.However, the corrosion just initiates and develops in wet cyclic period, and suspends during the dry cyclic period when they are exposed to dry-wet cyclic environment. Besides, when the magnesium alloys with Y additions are exposed to the wet environment again, the original filiform corrosion does not extend any more, but new filiform corrosion can be found in other location. With the increase of dry-wet cycles, the number of filiform corrosion on the surface of magnesium alloys increases. The effect of rare earth Y on refining the grain of secondary phase and decreasing the Al distribution along the grain boundaries of the secondary phase leads that hydrogen evolution can not be impeded easily, and corrosion develops in the way of continued hydrogen evolution along the end of corrosion location. This is the reason why the filiform corrosion morphologies form. Electrochemicalimpedance spectra measurements indicate that the charge transfer resistance tested in dry-wet cyclic environment is much lower than that in immersion environment, suggesting that the magnesium alloys suffer heavier corrosion in dry-wet cyclic environment, which is relate to that the time of hydrogen evolution is prolonged under thin electrolyte layers and the integrity of the surface film of magnesium alloy is broken because of the drying effect under dry environment.
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