真空镀带钢锌镁合金的制备与耐蚀机理研究

【作者】 马进；

【导师】 沈杰；

【作者基本信息】 复旦大学 ， 物理电子学， 2012， 硕士

【摘要】 钢铁的防腐蚀性能是钢铁工业的一个重要研究领域,在钢铁表面形成保护层己成为钢铁防腐蚀的重要手段。作为一种新型的锌基合金镀层,锌镁合金镀层由于其优异的耐蚀性能正逐步受到人们的重视。相对于传统的湿法电镀和热浸镀,真空镀得到的镀层具有优良的附着力、致密度、可加工性和耐腐蚀性,因此真空镀成为一种很有竞争力和发展前途的制备工艺。因此,对锌镁合金镀层的真空镀制备工艺和耐蚀性能的研究具有重要的科学意义和巨大的潜在应用价值。本文采用在镀锌钢板上真空蒸发沉积镁后快速退火的工艺形成锌镁合金镀层。研究工作主要包括：制备工艺对锌镁合金镀层组分的影响,热处理时形成锌镁合金的过程,锌镁合金镀层的防腐蚀性能,以及锌镁合金镀层的防腐蚀机理。主要结果如下：(1)退火工艺对合金化的影响：退火温度较低时,不会形成锌镁合金；退火温度越高,形成的锌镁合金相种类和晶面取向越多,合金化程度越高；退火温度过高会导致铁锌合金相生成。退火时间对合金化也有类似规律,随着退火时间的增长,合金种类和晶面取向增多,继续增长退火时间则会出现铁锌合金。(2)锌镁镀层扩散研究：在快速退火过程中,镁扩散进入锌层并在一定深度富集,先以单质形式存在,继续退火会形成锌镁合金。镁富集区具有扩散阻挡效应,阻碍镁进一步向内部扩散的同时也阻碍铁向表面的扩散。(3)锌镁合金防腐蚀性能研究：退火温度不变,有最佳的退火时间,使得生成红锈的时间增长最多,约为纯锌样品的7倍；在退火时间较长时(240s),退火温度越高,锌镁合金样品出现红锈的时间越短,主要原因是由于退火温度升高后导致亚表面生成的铁锌合金。(4)锌镁合金防腐蚀机理研究：锌镁合金镀层腐蚀分为钝化层形成、钝化层溶解和锌层溶解三个阶段。当表面还有较多镁单质存在时,则首先有镁的溶解过程。钝化膜的主要成分为氧化镁、氢氧化镁和氢氧化锌,随着锌镁合金不断被消耗,钝化膜局部分解并最终消失,进入锌层保护钢板的阶段。钝化膜的形成是锌镁合金具有优异防腐蚀性能的主要原因。更多还原

【Abstract】 Corrosion resistance is an important research field in the steel industry. To plate a protective coating on steel is a major approach to resist corrosion. As a new type of zinc-base alloys coatings, zinc-magnesium alloys coating has drawn more and more attention. Because coatings prepared by vacuum plating have better adhesion, compactivity, machinability and corrosion resistance than those prepared by traditional wet plating and hot-dip plating, vacuum plating is becoming a competitive and promising preparation method. Therefore, studies on vacuum plating and properties of coating prepared by this means have great scientific significance and huge potential application value.Vacuum evaporation was applied to deposit magnesium on galvanized steel in this dissertation. Fast annealing was then used to prepare Zn-Mg alloys. The research approach is as below:components and organization structures of Zn-Mg alloys coating were studied; the alloying process under thermal treatment was analyzed; the corrosion resistant properties were tested; and the corrosion mechanism was explored. The main conclusions are:(1) Conclusion of the studies on the thermal treatment:Zn-Mg alloys cannot be formed at a relatively low temperature; with the increase of the temperature, more Zn-Mg alloys are formed; Fe-Zn alloys can be formed at a relatively high temperature. The annealing time dependency follows the similar rule, that is, as the annealing proceeds, alloy types and grain orientations increase, and Fe-Zn alloys are formed.(2) Conclusion of the studies on diffusion:magnesium is enriched within zinc layer during the diffusion. Zn-Mg alloys are formed during the mutual diffusion. The magnesium enrichment has barrier effect, which prohibits inward diffusion of magnesium and outward diffusion of iron.(3) Conclusion of the salt spray test:there is an optimal annealing time, which results in approximately7-fold hours for the formation of the red rust; when annealing time is relatively long, with the increase of the temperature, the red rust is formed at a faster rate due to more Fe-Zn alloys at sub-surface.(4) Conclusion of the electrochemical experiment:corrosion process of Zn-Mg alloys coating consists of three stages-the formation of the passive layer, the dissolution of the passive layer and the dissolution of the zinc layer. When substantial magnesium exists on the surface, there is a stage of the dissolution of the magnesium before the other three stages. The studies on corrosion mechanism illustrate that the passive layer consists of magnesium oxide, magnesium hydroxide and zinc hydroxide, and the depletion of Zn-Mg alloys causes the decomposition of the passive layer. The main reason of the enhanced corrosion resistance is the formation of the passive layer.更多还原