镁合金表面磁控溅射Al膜的制备工艺及组织性能研究

发布时间：2019-05-19 07:57

【摘要】：镁合金是最轻的结构材料,具有许多优越的性能和广阔的应用前景,但其耐腐蚀性能较差的弱点是影响其应用的重要因素。提高镁合金的耐蚀性是当前镁合金开发与研究的重要课题,其中制备涂层是改善镁合金表面耐腐蚀性能的重要途径。在诸多涂层制备技术中,磁控溅射技术由于具有沉积速率高、膜层均匀、密度和纯度高、附着力强等优点被认为是制备表面涂层的最佳方法之一。基于铝有较好的耐腐蚀性能,本工作采用磁控溅射技术,在AZ91镁合金表面制备高纯铝膜,对膜层制备的工艺、膜层微观组织和腐蚀性能进行了研究。首先利用正交试验方法,以膜层耐蚀性以及界面结合力、膜厚和粗糙度为指标,对磁控溅射铝膜的溅射功率、基体加热温度、负偏压等工艺参数进行了优化,得到了对实验指标影响的参数顺序和获得良好综合性能的参数组合。其后对影响性能的主要工艺参数进行了单因素实验,研究了各参数对膜层组织和性能的影响趋势,依据膜层腐蚀机制分析了组织对耐腐蚀性能影响的原因。正交试验研究结果表明,影响膜层性能的磁控溅射工艺参数主次顺序为:溅射功率、基体加热温度、基体的负偏压、Ar气压强和溅射时间,磁控溅射铝膜的最优工艺参数组合为:溅射功率60W,溅射时间120min,基体加热温度200℃,Ar气压强2.1Pa,基体负偏压-150V。对铝膜的组织观察表明,完整的膜层可大致分为底侧的等轴晶区,等轴晶向柱状晶的过渡区,以及外侧的柱状晶区三个区域。改变工艺参数会使膜层的整体厚度和各区域的大小发生变化。提高溅射功率可增大膜层厚度,同时柱状晶区域扩大,等轴晶与柱状晶之间的过渡层变窄。提高基体加热温度和延长溅射时间时,膜层组织将也发生类似的变化。工艺参数对界面结合力也有明显的影响。随着溅射功率和基体加热温度的提高以及溅射时间的增加,界面结合力都呈现出先提高后降低的变化,当溅射功率为60W、基体加热温度为200℃、溅射时间为120min时,界面结合力最强。对试样腐蚀过程的分析表明,磁控溅射铝膜对镁合金基体可以起到一定的保护作用。对于铝膜的模拟汗液腐蚀来讲,腐蚀优先发生在膜层表面的晶界位置,并且沿晶界向膜层内部发展,一旦膜层局部腐蚀穿透,腐蚀介质将进入基体和铝膜层之间的界面,从而构成原电池加速腐蚀的进行,并导致膜层从基体上剥离。因此,膜层厚度尽可能大,且膜层以等轴晶区和过渡区为主,同时界面结合力强,是膜层具有良好腐蚀性能的重要条件。
[Abstract]:Magnesium alloy is the mildest structural material, which has many superior properties and broad application prospects, but the weakness of its poor corrosion resistance is an important factor affecting its application. Improving the corrosion resistance of magnesium alloys is an important topic in the development and research of magnesium alloys, and the preparation of coatings is an important way to improve the corrosion resistance of magnesium alloys. Among many coating preparation technologies, magnetron sputter technology is considered to be one of the best methods to prepare surface coatings because of its high deposition rate, uniform film layer, high density and purity, strong adhesion and so on. Based on the good corrosion resistance of aluminum, high purity aluminum film was prepared on the surface of AZ91 magnesium alloy by magnetron sputter. The preparation process, microstructure and corrosion properties of the film were studied. Firstly, the process parameters such as corrosion resistance, interfacial adhesion, film thickness and roughness of magnetron sputter aluminum films were optimized by orthogonal test, such as the deposition power, substrate heating temperature and negative bias voltage of the aluminum films deposited by magnetron, and the corrosion resistance, interfacial adhesion, film thickness and roughness of the films were optimized by orthogonal test. The parameter sequence affecting the experimental index and the parameter combination with good comprehensive performance are obtained. Then the single factor experiment was carried out on the main process parameters affecting the properties, and the influence trend of each parameter on the microstructure and properties of the film was studied. According to the corrosion mechanism of the film, the reasons for the influence of microstructure on the corrosion resistance were analyzed. The results of orthogonal test show that the primary and secondary order of magnetron sputtering process parameters affecting the properties of the film is as follows: sputtering power, substrate heating temperature, negative bias voltage of substrate, Ar pressure and sputter time. The optimum technological parameters of magnetron sputter aluminum film are as follows: sputter power 60W, sputter time 120min, substrate heating temperature 200C, Ar pressure 2.1Pa, substrate negative bias voltage-150V. The observation of the microstructure of the aluminum film shows that the complete film can be roughly divided into three regions: the isometric crystal region on the bottom side, the transition zone from the isometric crystal to the columnar crystal, and the columnar crystal region on the outer side. Changing the process parameters will change the overall thickness of the film and the size of each region. Increasing the sputter power can increase the thickness of the film, at the same time, the columnar crystal region is enlarged, and the transition layer between the isometric crystal and the columnar crystal becomes narrower. When the heating temperature of the substrate is increased and the sputter time is prolonged, the microstructure of the film will change similarly. The process parameters also have obvious influence on the interfacial adhesion. With the increase of sputter power, substrate heating temperature and sputter time, the interfacial adhesion increases at first and then decreases. When the sputter power is 60W, the substrate heating temperature is 200C, and the sputter time is 120min, The interfacial adhesion is the strongest. The analysis of the corrosion process of the sample shows that the magnetron sputter aluminum film can protect the magnesium alloy matrix to a certain extent. For the simulated sweat corrosion of aluminum film, the corrosion occurs first at the grain boundary position on the surface of the film, and develops along the grain boundary to the inner layer of the film. Once the local corrosion penetration of the film layer, the corrosion medium will enter the interface between the substrate and the aluminum film. Thus, the corrosion of the original battery is accelerated and the film is peeled off from the substrate. Therefore, the thickness of the film is as large as possible, and the film is dominated by isometric crystal region and transition zone, and the interface adhesion is strong, which is an important condition for the film to have good corrosion performance.
【学位授予单位】：内蒙古工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG174.44

【参考文献】