【作者】 方舒；

【导师】 魏云鹤；

【作者基本信息】 山东大学 ， 化学工艺， 2011， 硕士

【摘要】 热浸镀锌是钢铁防护的一种主要方法。但随着环境污染的日益加剧,传统的热镀锌产品已不能满足实际需要,因而,具有更高耐蚀性能的锌基合金镀层和特殊性能的镀层成为研究的热点。本文在课题组研究Zn-Al, Zn-Mg、Zn-Al-Mg合金镀层的基础上,选择加入微量的混合稀土以及钛、硼等元素,研究了锌基多元合金热镀工艺及其耐蚀性能。为减少合金元素的烧损,镀液中铝、镁、稀土、钛元素均以中间合金的方式添加,且在熔融合金表面采用熔剂保护。对加入不同含量的稀土及钛元素的锌基多元合金镀层,通过全浸试验和中性盐雾实验测定各试样的腐蚀失重速率。结果表明,在含稀土系列的合金镀层中,Zn-1%Al-2%Mg-0.15%Re合金镀层的腐蚀速率最小,耐蚀性能最好,稀土含量继续增加时,耐蚀性能反而有些降低。在含Ti系列镀层中,在Zn-1%Al基础上加入少量Ti也能提高镀层的耐蚀性能,且随着钛含量的增多,腐蚀速率先减小后增大,其中含0.05%Ti的耐蚀性能最优。对制备的合金镀层进行了电化学测试,结果表明,在Tafel极化曲线测试中,添加少量合金元素对极化曲线形状并没有较大的影响,加入稀土和钛均可以对镀层的电化学腐蚀起到抑制作用,其自腐蚀电位正移,线性极化电阻变大,自腐蚀电流变小。因此,加入稀土和钛均可以对镀层的电化学腐蚀起到抑制作用。无论是含稀土还是含钛系列的镀层,其电极的阻抗谱低频段均出现了一定程度的偏移,这与电极反应所生成的钝化膜有关,钝化膜的生成有利于耐蚀性能的提高。电化学测试结果与全浸试验相一致。在镀液中加入稀土元素,除了能够降低镀液的表面张力外,还能够除去镀液中的O、S元素,起到细化晶粒的作用,降低晶间腐蚀速率,提高耐蚀性能。在电镜图中可以看出,加入稀土元素后组织边界融合成为较浅的沟槽,经盐酸腐蚀后,腐蚀产物呈针状,腐蚀产物层较为致密。当Re添加量为0.1%时,对镀层晶粒的细化较为显著。加入钛后,镀层的表面为均匀的胞状组织,表观形貌有所改善。从截面的线扫描能谱中检测到混合稀土元素中含量较多的是铈元素,但并没有检测到钛元素。在对腐蚀产物的X-射线衍射分析表明,在加入镁、稀土元素以后,腐蚀产物中ZnO的量较少,存在较多的是碱式硫酸锌,且以沉淀物的形式附着在基体表面,附着力较强,能够防止镀层腐蚀向内部发展,提高耐蚀性能。此外,在物相分析中检测到锌铝的复杂氧化物的存在,在加入钛元素后,腐蚀产物中还有少量锌钛氧化物,这表明钛能够在提高耐蚀性能方面发挥作用,在镀层表面形成保护性好的氧化物薄膜,使腐蚀难以透过表层向内部深入。在所研究的合金镀层中,铝、镁、稀土、钛的加入量较少,热镀温度、热镀时间等工艺参数与传统热镀锌相比变化不大,可以在不改变热镀锌生产线的条件下进行生产,便于推广应用。更多还原

【Abstract】 Hot-dip is an effective and economical method of steel protection. But with the increasing environmental pollution, the traditional hot dip galvanized products can not meet the actual needs, and more and more attention has been paid to alloy coatings that have a higher corrosion resistance special properties.The 55%Al-Zn, Zn-Mg, Zn-Al-Mg coating have been further studied. Hot dip technology and corrosion resistance of a new alloy coating based on the previous studies was discussed in this article, which containing trace amounts of rare earth and titanium. Al, Mg, Re, and Ti were added in master alloys way. And in order to reduce the loss of alloying elements, the surface of molten alloy was protected with a new type of covering agent.The weight loss rate of alloy coatings with different content of Re and Ti were measured by immersion testing and salt spray testing to determine the corrosion resistance. The results showed that:the corrosion rate of Zn-1% Al-2%Mg-0.15% Re alloy coating is smallest, and have the best corrosion resistance, and when rare earth content continues increasing, corrosion rate decreases; in the containing Ti alloy coatings, small amount of Ti based of Zn-1% Al can also improve corrosion resistance of coatings. And with the Ti content increases, the corrosion rate decreases and then increases, and the one which contains 0.05% Ti is the lowest.Electrochemical test shows that the addition of rare earth and titanium all can inhibit electrochemical corrosion. The higher corrosion potential is, the smaller corrosion current density is. And the larger capacitive loop radius is, the greater the resistance of corrosion reactions has. The low frequency part of electrochemical impedance spectroscopy (EIS) of alloy coatings containing Re and Ti appear certain degree of migration. And it may be related to the formation of passive film which is conducive to the improvement of corrosion resistance. Electrochemical test results are consistent with the immersion test.The Re elements can reduce surface tension, remove O, S elements, play a role in grain refinement, and reduce intergranular corrosion rate. Organizational boundaries of coating containing Re integrated into the shallow groove. And the corrosion products after hydrochloric acid corrosion are denser comprised with pure zinc. The effect of grain refinement is the best when the content of Re reaches to 0.1%. The surface of coating containing Ti is uniform cellular organization, and the surface morphology qualities improve. Spectrum from the cross-section of the line scan detected cerium, but do not detect titanium.X-ray diffraction analysis shows that the corrosion products of coatings added Mg and Re are mainly in the form of alkaline zinc sulfate which can attach to the substrate surface to prevent corrosion to the interior of samples and improve corrosion resistance. In addition, zinc aluminum complex oxides are detected, which can increase the corrosion resistance. And in the coatings added Ti, there is a small amount of zinc titanium oxides, which indicates that the titanium element can play a role in enhancing by formation oxide film.The hot dip time and temperature of the new alloy is similar with the pure zinc, due to the low Al, Mg, Ti, and Re content in the coatings. On the basis of the original galvanizing line it can produce these new alloy coatings, so the coatings have wide application prospect.更多还原