【作者】 赵宇；

【导师】 周宏；

【作者基本信息】 吉林大学 ， 材料加工工程， 2007， 博士

【摘要】 镁合金因重量轻、比强度高、可再生受到青睐,在汽车、电子和航空航天等工业上的应用越来越广泛,有关镁合金的研究与开发以及生产工艺引起人们的高度重视,并取得了可喜成果。但是原料的组织和性能对生产件的影响,以及废料组织和性能对用废料生产的铸件的影响几乎没有人研究。本文利用A、B、C三厂生产的AZ91D和AM60B镁合金锭作为原料,分别将它们重熔,研究分析不同厂家的镁合金重熔前后的组织和性能,以及利用废料生产的镁合金的组织和性能;此外,进一步研究了过热温度、凝固速度、搅拌时间以及通过添加稀土元素Ce对镁合金重熔后组织的影响。结果表明,镁合金重熔后的组织和性能同对应的原料组织和性能基本相同或非常相近,具有明显的遗传性;镁合金遗传性随着过热温度的提高而逐渐降低;随着凝固速度的降低,组织遗传性增加;随着对合金液搅拌时间的增加,合金液结构被破坏,遗传性降低;随着稀土元素Ce含量的增加,镁合金的遗传性逐渐降低。镁合金在熔化过程中,存在的近程有序的原子集团,该集团具有和原料组织结构相同或相近的特性,这些原子集团也被称为团簇,合金液中的团簇(遗传因子)理论恰当地解释了镁合金的遗传性。更多还原

【Abstract】 With low density, relatively high intensity and stiffness, easier cutting processing capability and good shielding properties, magnesium alloy is recently used in most of industries, such as, automobile, electronics, aviation, etc. Researchers devote themselves to the production technology of magnesium alloy and obtain some results. However, nearly there is few research in the relationship of structure property and capability with materials and re-melting magnesium alloy, in fact, they does tie up. In this article the transmissibility of AZ91D and AM60B magnesium alloy, and the effect of re-melting temperature, rate of solidification, churning time, and by adding accession scrap were studied. The transmissibility of structure, impurity, capability and different re-melting technology are analysized which provides foundation for controlling transmissibility to structure and capability with Magnesium alloy.Three kinds of magnesium alloy from different plant A, B, and C to obtain corresponding re-melting magnesium alloy, and the chemical components were analyzised through optical spectrum analyzer. Their differences and intercommunity among the concerned magnesium were contrasted. As a result, it was found that the structure and property of re-melting magnesium alloy was similar to that of the original materials. After adding different percent content scrap, the quantity of re-melting magnesium alloy changed with content of added scrap, and such rule was studied. The result shows that when the content of added scrap is lower than 25%, there is no obvious difference in the structure and property between re-melting magnesium alloy and original material. When the content is over 75%, structure and property of re-melting magnesium alloy is obviously different from that of original material, and are nearly same to that of re-melting scrap. When the content is within 25%~75%, the structure and property is between that of the original material and alloy and re-melting scrap. It is found that it is magnesium alloy remaining the structure and property of original material during the re-melting process results in the comparability and intercommunity between re-melting magnesium and original material.When some scraps were added into original material, the quantity of impurity increased, thus the casting mechanical features drop down. It is found that the component element of impurity in product is as same as the original scrap’s by analysis with EDAX, and the content of same element is similar. The impurity of re-melting magnesium alloy with adding scrap is same with that of impurity of scrap. These impurities mainly include inner and exterior impurities. But the granularity is getting less and nearly same with that of scrap, so the rigidity becomes harder which shows the transmissibility of original materials performance.In addition, AZ91D and AM60B magnesium alloy with different temperature were re-melted and casted with different concretionary speed and mix-round time. The result shows that when remelting temperature is over 750℃, the original structure is nearly completely destroyed, the structure transmissibility is radical disappear. The higher concretionary speed is less transmit the structure and property of original material, the low concretionary speed is favorable to comeback of structure, so the structure transmissibility is strong with the drop of concretionary speed. The churning time will weaken the transmissibility of Magnesium alloy. When churning time is over a certain numerical value, the structure of re-melting alloy will have no obvious change.RE can alter the heredity of the microstructure of the die-cast magnesium alloy, and effect the heredity of the microstructure on magnesium alloy; when the content of RE is 0.5%, the heredity of the microstructure still exists. As the content increasing, the heredity begins to destruct, and when the content of RE is 1.5%, the heredity of the microstructure vanishes completely. The effect of RE on the heredity of the microstructure and property of the magnesium alloy is because the RE is the surface activity element, it can reduce interface energy and increase the crystal nucleus, generate a layer of adsorbed film on the surface of precipitated phase or growth phase, hindrance the crystal grain grow up, refine crystal grain, and reduce the possibility of short-range order atomic group as crystal nucleus or crystal embryo growing up crystal grain, and reduce the possibility of the heredity of the microstructure.The re-melting process and transmissibility of magnesium alloy during remelting process were analysized by DTA. According to the atomic clusters theory of alloy liquid, it is found that the structure theory of transmissibility to magnesium alloy and thermodynamics analysis, and the transmissibility of magnesium alloy during the process of solid-melt-solid. Through studying the r-melting process of magnesium alloy, it is found that the asymmetrical regions are gradually lessening. The clusters of asymmetrical microstructure and inordinate regions in between them make up of the melt. The clusters of asymmetrical microstructure reserve some characteristic of original material of Magnesium alloy, so the macroscopically asymmetry of melt is inherited. The asymmetrical structure of melt remains the material asymmetry of magnesium alloy. During the process of solidification, the structure asymmetry effects on the structure and performance of new cast, so the cluster theory is correct to metallic transmissibility by thermodynamic analysis.更多还原