镁合金防腐复合涂层的制备及耐蚀性研究

发布时间：2018-12-16 07:11

【摘要】：镁合金作为新世纪新型绿色材料,具有很多其它金属无法比拟的优点,如密度小,强度高,电磁屏蔽好等特点,在通讯、汽车、电子等行业具有很大的应用潜力。但是,镁合金的耐蚀性较差,这大大限制了镁合金大范围的应用,如何提高镁合金的耐蚀性成为镁合金进一步推广应用所要解决的首要问题。为了使镁合金的优势充分发挥,很多耐蚀涂层被研究开发。如金属镀层、有机涂层、化学转化膜、阳极氧化等。但是,这几种方法均有一些缺陷。化学转化膜制备方法简单,但是膜的致密性差,容易开裂,无法阻止镁合金基底的腐蚀;阳极氧化能够在镁合金表面形成多孔的氧化膜,在一定程度上降低镁合金的腐蚀速率,但是由于表面孔洞的存在,单层氧化层无法长久保护镁合金基底,腐蚀介质易进入孔洞腐蚀镁合金基底;电镀和化学镀镀层一般分为阳极镀层和阴极镀层,最常见的镁合金防腐的金属镀层为镍磷合金镀层,作为阴极镀层的最大的缺点就是如果镀层存在微孔将加速镁合金基底的腐蚀,基底在很短时间内产生穿孔,且施镀步骤复杂,耗能大。本论文主要研究镁合金防护的新方法,为镁合金的防腐提供新思路,进一步提高镁合金的耐蚀性,扩大其使用范围。涂层的宏观及微观形貌分别用光学显微镜和场发射扫描电子显微镜(FESEM)表征。涂层成分及元素含量采用色散X射线光谱(EDS)测定。通过浸泡试验、电化学极化、电化学阻抗等测试方法表征涂层的形成机理及涂层的耐蚀性。主要研究内容如下:1.研究并讨论了镁合金化学镀双层镀层的防护与腐蚀机理。针对当前镁合金化学镀镍存在的孔洞问题,提出了双层镀施镀方案,以化学镀Ni-P层作为内层,化学镀Ni-B作为外层,研究了最佳工艺条件参数。采用盐雾以及电化学手段对镀层的腐蚀行为进行了检测,并提出了双层镀层的腐蚀机理。2.开发了非活性基底的一种非钯活化工艺,并优化了工艺条件,最终在微弧氧化层上获得均匀致密的化学镀镍层。微弧氧化层作为内层,具有多孔结构,能够为化学镀层提供足够多的机械咬合点,且在一定程度上减小镁合金基底与化学镀镍层之间的电偶腐蚀的发生。化学镀镍层作为外层能够对微弧氧化层起到封孔的效果。3.研究了镁合金表面超疏水镀层的制备工艺,采用化学镀和电镀相结合的方法在镁合金表面获得疏水层,该涂层由内层化学预镀镍,中间层电镀铜和外层电镀镍层组成。化学预镀镍使试样表面电场分布相对均匀,电镀铜层起到加厚镀层及作为阻挡层的作用。电镀镍使得表面形成粗糙结构,而粗糙表面是超疏水结构形成的一个重要因素。然后通过简单的浸泡方法对镀层表面进行修饰,获得超疏水层。4.研究开发了一种镁合金化学电泳复合涂层方法。采用电化学氧化的方式使镁合金表面形成氧化层,然后通过化学电泳的方式在镁合金表面获得一层致密的较厚的涂层。当氧化试样放入电泳漆中时,氧化层的Mg O或者Mg(OH)2与电泳漆中的树脂阳离子发生反应,不溶性的树脂沉积在试样表面形成涂层。对涂层的结构及耐蚀性进行了实验研究。本论文在如下方面有创新性研究工作:(1)在镁合金表面制备了高耐蚀性的Ni-B/Ni-P双层镀层,并探究了双层镀层高耐蚀性的原因。(2)采用一种新型的非活性基底活化剂,在镁合金微弧氧化层上获得了化学镀镍层,大大降低了活化剂成本。研究了新型活化剂的活化机理及所得到的复合涂层的腐蚀机理;(3)开发了一种具有超疏水性质的功能性镀镍层,对镀层的结构、耐蚀性及疏水机理进行了探究。(4)开发了一种镁合金化学电泳复合涂层防护技术,并对所得复合涂层的耐蚀性进行了研究。
[Abstract]:As a new type of green material in the new century, the magnesium alloy has the advantages of many other metals, such as small density, high strength, good electromagnetic shielding and so on, and has great application potential in the fields of communication, automobile and electronics. However, the corrosion resistance of the magnesium alloy is poor, which greatly limits the application of the large range of the magnesium alloy, and how to improve the corrosion resistance of the magnesium alloy is the first problem to be solved by the further popularization and application of the magnesium alloy. In order to give full play to the advantages of the magnesium alloy, many corrosion-resistant coatings have been developed. such as a metal coating, an organic coating, a chemical conversion film, an anode oxidation, and the like. However, there are some drawbacks in these methods. The preparation method of the chemical conversion film is simple, but the compactness of the film is poor, the cracking is easy, the corrosion of the magnesium alloy substrate can not be prevented, the anodic oxidation can form a porous oxide film on the surface of the magnesium alloy, and the corrosion rate of the magnesium alloy can be reduced to a certain extent, but due to the existence of the surface hole, the single-layer oxide layer can not protect the magnesium alloy substrate for a long time, the corrosion medium is easy to enter the hole to erode the magnesium alloy substrate, the electroplating and the chemical plating plating layer are generally divided into an anode plating layer and a cathode plating layer, and the most common corrosion-resistant metal plating layer of the magnesium alloy is a nickel-phosphorus alloy coating, the biggest disadvantage of the cathode coating is that if the coating is present with a micro-hole, the corrosion of the magnesium alloy substrate is accelerated, the substrate is perforated in a very short time, and the plating step is complex and the energy consumption is large. This paper mainly studies the new method of magnesium alloy protection, and provides a new thought for the corrosion protection of the magnesium alloy, and further improves the corrosion resistance of the magnesium alloy and expands the application range thereof. The macroscopic and micro-morphology of the coatings were characterized by an optical microscope and a field emission scanning electron microscope (FESEM), respectively. The content of the coating and the content of the element were determined by dispersive X-ray spectroscopy (EDS). The formation mechanism of the coating and the corrosion resistance of the coating were characterized by immersion test, electrochemical polarization and electrochemical impedance. The main content of the study is as follows: 1. The protection and corrosion mechanism of magnesium alloy electroless plating double-layer coating was studied and discussed. In order to solve the problem of the existing holes in the electroless nickel plating of the magnesium alloy, a double-layer plating scheme was proposed, and the optimum process condition parameters were studied by electroless Ni-P layer as the inner layer and the electroless Ni-B as the outer layer. The corrosion behavior of the coating was tested by salt spray and electrochemical method, and the corrosion mechanism of the double-layer coating was put forward. A non-active activation process for inactive substrates was developed, and the process conditions were optimized, and a homogeneous and dense electroless nickel plating layer was finally obtained on the micro-arc oxidation layer. the micro-arc oxidation layer is used as an inner layer and has a porous structure, so that a sufficient mechanical bite point can be provided for the chemical plating layer, and the occurrence of the electric coupling corrosion between the magnesium alloy substrate and the chemical nickel-plating layer is reduced to a certain extent. the chemical nickel-plating layer can be used as the outer layer to effect the micro-arc oxidation layer as a sealing hole. The preparation process of the super-hydrophobic coating on the surface of the magnesium alloy was studied. The hydrophobic layer was obtained on the surface of the magnesium alloy by the combination of electroless plating and electroplating. The coating was composed of the inner layer of chemical pre-plating, the intermediate layer of copper plating and the nickel layer of the outer layer. the chemical pre-nickel plating makes the electric field distribution of the surface of the sample to be relatively uniform, and the electroplated copper layer plays a role of thickening the plating layer and serving as a barrier layer. Electroplated nickel causes the surface to form a rough structure, and the rough surface is an important factor in the formation of super-hydrophobic structures. and then the surface of the plating layer is modified by a simple soaking method to obtain the super-hydrophobic layer. A method for composite coating of magnesium alloy by chemical electrophoresis was developed. the surface of the magnesium alloy is formed into an oxide layer by means of an electrochemical oxidation, and then a dense thick coating is obtained on the surface of the magnesium alloy by means of chemical electrophoresis. When the oxidation sample is put into the electrophoretic paint, the Mg O or Mg (OH) 2 of the oxide layer reacts with the resin cation in the electrophoretic paint, and the insoluble resin is deposited on the surface of the sample to form a coating. The structure and corrosion resistance of the coating were studied. The paper has the innovative research work in the following aspects: (1) The Ni-B/ Ni-P double-layer coating with high corrosion resistance is prepared on the surface of the magnesium alloy, and the reason of the high corrosion resistance of the double-layer coating is also investigated. and (2) a novel non-active base activator is adopted, a chemical nickel-plating layer is obtained on the magnesium alloy micro-arc oxidation layer, and the cost of the activator is greatly reduced. The activation mechanism of the new activator and the corrosion mechanism of the composite coating were studied. (3) a functional nickel-plated layer with super-hydrophobic property was developed, and the structure, corrosion resistance and hydrophobic mechanism of the coating were explored. (4) The protective technology of magnesium alloy chemical electrophoresis composite coating was developed, and the corrosion resistance of the obtained composite coating was studied.
【学位授予单位】：湖南大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG174.4

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