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1、 上海交通大学硕士学位论文 ICa 和 Ti 对镁合金抗氧化性和力学性能的影响 摘 要 镁合金具有比重小、比强度比刚度高、阻尼减震性能优良、切削加工性能好、电 磁屏蔽能力强、尺寸稳定和容易回收等诸多优点，近年来已成为汽车、通讯电子和航 空航天领域重要的轻质金属结构材料，显示了极大的应用前景。我国具有丰富的镁资 源，原镁产量和出口居世界首位，但是镁合金的研究和应用还比较落后。如何将我国 的镁资源优势转变为技术和经济优势，促进国民经济发展，是摆在我们面前的迫切任 务。因此，开展镁合金研究对于我国的经济和建设具有十分重要的意义。 本文以 AM50 和 AZ91 合金为基，通过添加 Ca 和 Ti,
2、浇铸后经挤压或轧制制备 了几种不同成分的实验合金，开展了如下的研究：(1)测试了各实验合金的燃点，通 过扫描电子显微镜(SEM)、 X 射线衍射仪(XRD)、 电子探针(EPMA)、 俄歇电子能谱(AES) 等分析和测试手段，系统研究了含 Ca 或 Ti 的 AM50 和 AZ91 镁合金氧化膜的结构， 并探讨了其氧化机理。(2)研究了合金元素 Ca 或 Ti 对挤压和轧制 AM50 镁合金显微 组织和力学性能的影响。(3)测试了含 Ca 或 Ti 的挤压和轧制 AM50 镁合金热处理后 的力学性能，研究了热处理过程中合金组织的演化规律，探讨了热处理强化机制。(4) 测试了含 Ca 或 Ti
3、的挤压和轧制 AM50 镁合金的蠕变性能， 分析了其蠕变强化机制。 研究表明，Ca 能显著提高 AZ91 和 AM50 镁合金的燃点，测得 AZ91+1Ca 和 AM50+1Ca 的燃点分别高达 860和 874；Ti 对 AZ91 和 AM50 镁合金的燃点有小 幅提高。宏观及微观观察表明，Ca 的加入使 AM50 和 AZ91 合金的表面形成了一层 致密均匀的具有保护性的氧化膜, 而Ti加入AZ91和AM50合金后形成的氧化膜虽然 比较规则，但不连续不致密，不具保护性。以 AM50+xCa(x=0,1,2%)为例，分析了氧 化膜的组成和结构， 发现 AM50+xCa(x=1,2%)合金的氧
4、化膜主要由 MgO 和 CaO 组成， 从 AES 曲线反映的氧化膜剖面上各元素的浓度分布可以把氧化膜分成两个亚层，最 外层主要由 CaO 组成，内层主要由 MgO 组成，并从热力学的角度论证了这种推论。 含 Ca 的 AM50 镁合金挤压或轧制后，其显微组织比对应的铸态组织明显细化， 晶粒及第二相沿加工方向分布并出现了孪晶组织， Al2Ca 相形成并抑制 Mg17Al12相的 生成，由于 Al2Ca 相热稳定性较高，因此可以显著提高合金的高温力学性能和蠕变性 能；挤压和轧制 AM50 合金添加 Ti 后，其显微组织明显细化，力学性能显著提高。 挤压 AM50+xCa 镁合金的固溶处理是第二相
5、 Mg17Al12快速溶解于基体而 Al2Ca 逐步变细变小并断开成为颗粒的过程；时效处理是 Mg17Al12相以细小粒状从过饱和 的基体中析出的过程。热处理后，拉伸性能有所改善，但效果不是很明显。 添加 Ca 后， 挤压和轧制 AM50 镁合金在蠕变过程中有细小的 Al2Ca 和 CaMnxAl2-x 相从基体析出，与原有的 Al2Ca 相一起，对合金蠕变性能的提高起到有益作用，其蠕 变强化机制为晶界强化，位错钉扎和位错攀移。 关键词：镁合金，抗氧化，挤压，轧制，固溶，时效，蠕变，力学性能 上海交通大学硕士学位论文 IIEffect of Ca and Ti on Oxidation Res
6、istance and Mechanical Properties of Magnesium Alloy Abstract Magnesium alloys, as the lightest structural metal, have been widely used in automobile, electronics and aerospace industries for their low density, high ratio strength and stiffness, good damping and casting capability, which show infini
7、te applied prospect. China has abundant magnesium resource, whose output and export of magnesium is largest among all the countries. However, the research and application of magnesium in China is rather lagged contrasted with other developed countries. How to translate magnesium resource predominanc
8、e into technology and economy advantage and promote the development of national economy is an urgent task for us. So it is very significant to carry out the research on magnesium alloys. In the paper, several alloys were prepared by adding calcium and titanium into AM50 and AZ91 magnesium alloys. Th
9、en the as cast alloys were rolled and extruded into samples. First, ignition temperature of the samples was tested. After testing ignition temperature, oxide film of the AM50+xCa(x=0, 1, 2wt.%) alloys was examined using scanning electron microscopy(SEM), electron probe microanalysis(EPMA)，x-ray diff
10、raction(XRD) and Augur electron spectrometer(AES). The structure and composition of oxide film was systematical studied and the oxidation mechanism was discussed. Second, the effects of alloys element (Ca and Ti）on the microstructure and mechanical properties of extruded or rolled magnesium alloys w
11、ere researched. Third, the mechanical properties of extruded or rolled AM50 magnesium alloys containing calcium and titanium after heat treatment were tested, microstructure evolution during heat treatment was analyzed and mechanism of heat treatment strengthening was discussed. Fourth, Creep proper
12、ties of extruded or rolled AM50 magnesium alloys containing calcium and titanium were tested and the mechanism of creep strengthening was discussed. The research indicated that calcium addition could increase the ignition temperature of AM50 and AZ91 magnesium alloys while titanium addition had litt
13、le effect on the 上海交通大学硕士学位论文 IIIignition temperature of AM50 and AZ91magnesium alloys. After adding calcium, compact uniform oxide film formed on the surface of alloys so it is protective; after adding titanium, oxide film was rather regular but not continuous, so it is not protective. Taking AM50+
14、xCa(x=1, 2%) magnesium alloy for example, the structure and composition of oxide film with oxidation resistance was studied. We found that the oxide film of AM50+xCa(x=1, 2%) alloys consisted of compound of CaO and MgO and this oxide film could be divided into two layers according to the element dis
15、tribution curve along the section of oxide film which. The outer layer mainly consisted of CaO and the inner layer mainly consisted of MgO. This conclusion was proved by thermodynamic point of view. After extrusion or rolling, the grain of AM50 based magnesium alloys were refined, their microstructu
16、re and second phase distruibuted along the processing direction and twin structure occurred. When Ca was added into AM50 magnesium alloy, Al2Ca phase formed and restrained the formation of Mg17Al12 phase. Al2Ca phase had excellent thermal stability so it can increased the high temperature mechanical properties and creep resistance of wrought AM50 magnesium alloy prominently. When Ti was added into wrought AM50 alloy, grain was refined remarkably and mechanical properties were incre
