镁合金彩色金相研究

重庆大学硕士学位论文镁合金彩色金相研究姓名：付启涛申请学位级别：硕士专业：材料科学与工程指导教师：潘复生2010-05中文摘要摘要彩色金相是金相技术发展后期才出现的一种先进的金相显示技术，它综合了光学、化学、色彩学等多个学科的知识，充分光的各种特性，使材料不同组织显示出不同颜色，与传统黑白金相相比体现出明显的优势。

一般来说，它具有更高的鉴别能力，能显示晶界、枝晶、第二相和成分偏析等，提供更多关于材料显微组织的有用信息，并能提高组织显示的精确性。

这种技术在钢铁、铝合金等传统材料已有非常成功的应用，但在镁合金上的应用才刚刚开始，对大多数镁合金而言是应用空白。

对镁合金的彩色金相分析技术进行研究，对镁合金组织的精细研究和镁合金材料的发展具有十分重要的意义。

本文对常用镁合金组织彩色金相的制样、形膜和观察方法进行了研究，主要包括：各类抛光方法制样的表面质量对彩色金相效果的影响；化学浸蚀形膜法，包括各种配方的腐蚀剂在不同腐蚀时间下对对形成彩色金相的影响；试验了离子溅射形膜法形成彩色金相的效果；考察了设备参数对彩色照片效果的影响等。

研究结果表明，机械抛光对试样表面化学作用最小，得到的彩色金相衬度最好，但是试样表面划痕问题不容易解决；化学抛光可以在很大程度上消去划痕和变形层，对低合金含量的镁合金效果较好，但对高合金含量的试样表面有较深的腐蚀，严重影响最终的彩色衬度；电解抛光在本实验条件虽然也能去除划痕，但是使试样表面发黑、产生蚀坑或者泛白、出现干扰网格等，不能满足彩色金相所需的磨面条件。

研究结果表明，在腐蚀剂方面，试剂1（乙酸1ml、乙醇150ml、水50ml）对显示铸态或均匀化的低铝含量镁合金AZ31和铸态的ZK60都没有什么效果，而对高铝含量的铸态AZ91的效果不错，显示出其彩色晶粒衬度和枝晶；试剂2（苦味酸6g、乙酸2ml、乙醇100ml、磷酸0.5ml、水1ml）在浸蚀2~4min的条件下适用于全系列AZ系列镁合金，对铸态ZK60没有好的效果；试剂3（苦味酸3g、乙酸20ml、乙醇50ml、水20ml）没有什么好的效果，试样均腐蚀严重；5%~15%的乙酸-饱和苦醇试剂对AZ系镁合金具有较好的显示效果，其功能与试剂2相似；其它羧酸、乙二醇、无机酸、含铬盐、焦亚硫酸盐、铵盐、高锰酸钾等的水或/和酒精溶液在本实验条件下均只能得到铸态镁合金简单第二相的相关信息，没有彩色金相效果；离子溅射镀金的方法可以增强明场下的第二相的颜色衬度，但效果并不太理想，相比化学蚀刻沉积，效果要差得多，而且其价格昂贵，并不适用于普遍使用。

本实验条件下的热染也没有任何彩色金相效果。

显微镜和照相系统的很多参数对最终的彩色衬度都有影响。

氙灯光源比卤素灯具有重庆大学硕士学位论文更高的亮度和色温，具有更接近日光的连续可见光谱，适用于彩色金相；偏光是否正交是本实验条件下影响彩色衬度的关键因素，绝大部分情况下只有在正交条件下才能得到满意的衬度；灵敏色片可以提高偏光干涉序级，增强颜色衬度；各晶粒颜色以180º为周期随着载物台的旋转而变化；相机白平衡几乎不影响金相的颜色衬度，但改变颜色色调，日光白平衡条件下得到的颜色最接近真实金相颜色。

在本实验条件下利用微分干涉衬度没有得到有用的彩色金相效果。

关键词：镁合金，彩色金相，化学腐蚀，离子溅射，热染英文摘要ABSTRACTColor metallography is an advanced optical technique which arose in the late development stage of metallography. It involves many other disciplines, such as optics, chemistry, and color science, making the fullest use of the properties of light to distinguish different phases and structures of materials. It has many advantages compared to common black-white metallography. Generally, color metallography has a much higher ability to display grain structure, dendrite structure, second phases, and composition segregation, providing scientists with more accurate and useful information regarding the microstructure of materials. This technique has been applied successfully on steel and aluminum alloys. However, its application on magnesium alloys is still in its early stages. Research into the application of color metallography for magnesium alloys is significant for the meticulous study of its microstructure and development.In the present work, the specimen preparation, forming of films, and observations of staple magnesium alloys were discussed. The affects of surface quality obtained from different preparing methods on color metallography were also examined. Chemical etching was researched, including the effects of different formulations over different periods of time on the formation of color metallography. The Ion sputtering of aurum was tested on specimens in order to obtain color contrast. The effects of the parameters of the instruments on the color metallography were also studied.The results show that optimal color contrast can be achieved through the process of mechanical polishing, since it has the smallest chemical effect on the specimen. However, the main problem with mechanical polishing is that the marking is hard to remove. Fortunately, chemical polishing is useful to remove the scarred and deformed layer. It works well on magnesium alloys with low alloy content, but it attacks the surface of specimens with high alloy content, which ultimately affects the final color contrast significantly. Electrolytic polishing is not suitable for the specimen preparation of magnesium alloys under present experimental conditions, although it cures the scarification. It leads to either a black and pitted surface or a whitish and gridding surface, both of which fail to meet the surface quality requirements of color metallography.Considering the regents, reagent #1 did not work on as-cast or homogenized magnesium重庆大学硕士学位论文alloys with low aluminum content, such as AZ31 or as-cast ZK60. H owever, reagent #1 is useful for revealing color grain contrast and the dendritic crystals of as-cast AZ91 (which has a higher content of aluminum). Reagent #2 works well on all AZ series of magnesium alloys, yet it has little effect on as-cast ZK60. Reagent #3 severely etched the specimens and returned no useable results. The results of using Acetic picral with 5-10% acetic acid content were similar to reagent #2, working well on AZ series magnesium alloys. Only limited second phases information was obtained, and no color metallography was achieved by other reagents including water and/or alcohol solutions of other carboxylic acid, glycol, inorganic acid, chromic salt, pyrosulfite, ammonium salt and potassium permanganate.An enhanced yet limited second phases figure can be obtained by ion sputtering aurum. It has only a limited affect, and is very expensive compared to chemical deposition. Therefore, it is not fit for universal application. Also, no useful color metallography was obtained via the process of heat tinting.Many parameters of the microscope and photography system had a significant effect on the final color contrast. Xenon lamps are much brighter and have a higher color temperature than halogen lamps. They have a continuous spectrum, similar to sunlight, which is quite suitable for color metallography. During this study, optimal contrast could only be achieved by crossed polarized light in most cases. Sensitive tint filters were used to raise the interference level so that the color contrast could be enhanced. The grain color contrast varies with a period of 180°when the objective stage rotates. The white balance of the camera does not affect the contrast between grains, yet it does change the color. A color contrast which is closest to natural colors can be obtained when the white balance of the camera is set to sunlight. Differential interference contrast generated no useful color contrast in this study.Key Words: Magnesium alloys, Color metallography, Chemical etching, Ion sputtering, Heat tint.1 绪论1 绪论1.1 镁合金的发展前景镁是地球上储量最丰富的元素之一，在地壳表层、盐湖和海洋中都有着丰富的含量，在很多金属资源趋于枯竭的今天，发展镁金属材料是实现可持续发展的重要措施之一。