【作者】 陈绪宏；

【导师】 丁培道；

【作者基本信息】 重庆大学 ， 材料学， 2003， 硕士

【摘要】 本文以Φ480 ZK60 镁合金工业铸锭为研究对象，分别对铸锭的宏观组织结构、显微组织的合金相构成，以及凝固冷却速率(v)对铸锭组织结构的控制作用进行了定性及定量的探索性的实验研究。通过光学显微镜的观察试验研究了该铸锭的宏观组织结构。结果表明，该铸锭由全等轴晶组织构成。晶粒外形为花朵状，晶粒在长大初期以树枝形式发展，后期以近胞状方式发展，这一特点在整个等轴晶区内的不同区域无明显差异。就晶粒形态和Φ405 AZ31 镁合金铸锭、Φ130 ZK60镁合金铸锭以及Gleeble凝固模拟试验所得的ZK60铸态试样作了对比研究。用定量金相法测定了Φ480 ZK60 镁合金铸锭的晶粒尺寸及其沿铸锭径向的变化，用统计的方法得到铸锭的平均晶粒弦长约为160，其对应的ASTM晶粒度等级为2级，其中铸锭中心区域的晶粒弦长大约为230, 是边缘区域的2.3倍。用金相显微镜结合透射电子显微镜(TEM)研究了Φ480 ZK60镁合金铸锭的显微组织形貌及合金中不同相的特点。对合金相进行了电子衍射(ED)分析，用计算电子衍射斑的方法确定了几种主要合金相。实验结果表明，凝固共晶时被离异到晶间的-Mg7Zn3相最终形成了（+Mg3Zn2）伪共析组织。在晶粒之间的细小缝隙中存在以微小粒状形式团聚的相，试验证明为凝固末期形成的相。以颗粒形式在晶内脱溶析出，且该颗粒在晶内分布不均匀。在金相试验中还发现了新奇浸蚀花样，疑为由显微偏析造成。对此花样用电子探针（EPMA）进行了线扫描分析，结果表明，在晶内或者晶界处有富Zr核，Zn 的含量从枝晶心部至外部逐渐升高，Zr则相反。Zn在凝固前期形成的树枝晶中的含量要明显低于后期依附在树枝上以胞状形式凝固的晶体中的Zn含量。用Gleeble 1500热模拟机获得不同凝固冷却速率v的ZK60镁合金试样，在测量各试样的一次枝晶间距、二次枝晶间距后，用统计的方法获得了表征v-，v-依存关系的经验公式，从而得到了用凝固冷却速率控制铸锭结构的定量参考依据。试验还发现，ZK60镁合金铸态组织的维氏显微硬度HV与合金的二次枝晶间距有类似于Hall-Petch公式的关系，用统计回归的方法的到了表征-HV依存关系的经验公式。本文对上述所有结果分别进行了讨论，并对进一步研究工作提出了建设性意见。更多还原

【Abstract】 This paper aims at the properties of Φ480 ZK60 Mg alloy ingot. The macrostructure and microstructure of the ingot have been studied. Further more, the dependence between cooling rate (v) and dendrites space (λ) of ZK60 Mg alloy has been researched in Gleeble solidification experiment.Optical microscope is used to study ingot macrostructure. The results show that the ingot is made up of almost entire equal-axed grains. The grains grow in a dendrite-like way during the early stage of solidification and in a cell-like way during the later stage. As a result, the grains’ shape appears to be anthoid. This has been contrasted with Φ405 AZ31 Mg alloy ingot made by same casting procedure, and with Φ130 ZK60 Mg alloy ingot. Grain size has been measured by quantitative metallographical method, the average grain chord length is about 160 for the whole ingot, the corresponding ASTM Grain Size Number is 2. Therein, the grain chord length in the center region of the ingot is about 230, which is as 2.3 times long as it in the ingot edge region.Metallographical microscope and transmission electron microscope (TEM) have been used to observe the microstructure and to discover new alloy phases. Electron diffraction patterns have been used to calculate out the phase that found during the former experiments. Groundmass was found to be -Mg. Pseudo- eutectoid structure composed of -Mg + Mg3Zn2 is found in the small area between grain boundaries. It’s discovered that -MgZn2 congregats along grain boundaries as tiny pots. The precipitated particles inside grains proved to be -MgZn. Otherwise, a novel etched pattern is found during metallographical experiment, it’s supposed to be microsegregation of Zn and Zr. Electron probe (EPMA) line scanning experiments has been conducted to verify the presumption. The conjecture proved correct by the experimental results. In addiyion, Zr-rich Cores are found inside grains and grain boundaries.Gleeble1500 thermal simulation instrument is used to obtain ZK60 Mg alloy samples with various cooling rate (v) that can be calculated out according to the data recorded by the instrument. Primary Dendrites Space (λI) and Secondary Dendrites Space (λII) are measured for each sample. Empirical formulas about v-λI and v-λII are regressed with mathmatical method. The<WP=7>range of the formulas’ application is also analyzed.In addition, the dependence between micro-hardness (HV) and Secondary Dendrites Space (λII) for ZK60 cast alloy proved to be similar with Hall-Petch formula. And the empirical formula forλII-HV has been put forward in this paper either.All results have been discussed in this paper. Suggestions for further research also have been brought forward either.更多还原