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Mg作为一种典型的hcp结构金属,其枝晶形貌和生长取向受到多种因素的影响,目前针对镁合金中a-Mg枝晶生长模型的描述以及多样性的起源等问题的研究都比较缺乏,基于此,本文综述了本课题组在镁合金凝固微观组织结构三维表征方面取得的研究成果.借助同步辐射X射线微观断层扫描技术以及相场数值模型,研究了镁合金凝固过程中a-Mg(X)枝晶生长选择多样性的形成机理以及固溶合金元素(Al,Ca,Zn和Sn等)、固溶元素含量(溶质浓度)等因素对a-Mg枝晶生长选择和演化的影响.研究结果表明,固溶元素、固溶元素含量等因素都会对镁合金中a-Mg三维枝晶形貌和择优取向产生重要影响.在Mg-Ca和Mg-Al(hcp-fcc)合金中,枝晶倾向于以<1120>或<2245>为择优方向生长.在Mg-Sn(hcp-bct)合金中,等轴生长的枝晶沿着基面上<1120>和偏离基面的<112X>(X≈2)方向形成一种18次分支的结构,在Mg-Zn(hcp-hcp)合金中,a-Mg枝晶的择优取向会随着Zn含量的增加,从<1120>方向朝偏离基面的<1121>方向发生连续转变,并在转变的过渡区,发现了超支化的藻状枝晶结构,其原因可能是高各向异性Zn元素的引入带来的固/液界面自由能各向异性的变化.研究结果从一定程度上揭示了镁合金凝固过程中a-Mg枝晶生长形貌和分支结构选择多样性的规律.同时基于快速X射线成像技术率先开展了镁合金凝固过程三维微观结构演化原位表征研究,获得了镁合金凝固过程三维枝晶的生长演化过程.
Mg as a typical hcp structural metal, dendritic morphology and growth orientation by a variety of factors, the current magnesium alloys for the dendrite growth model description and the origin of the diversity of the issues such as research are compared In this paper, the research results of three-dimensional characterization of solidified microstructure of magnesium alloy are reviewed in this paper.Using synchrotron radiation X-ray micro-tomography and phase field numerical model, the effects of a- The formation mechanism of Mg (X) dendrite growth diversity, and the selection and evolution of a-Mg dendrite growth and the factors such as the content of alloying elements (Al, Ca, Zn and Sn) and the concentration of solute elements .The results show that the factors such as the content of solid solution element and solid solution element have an important effect on the morphology and the preferred orientation of a-Mg dendrites in Mg-Mg alloys.In Mg-Ca and Mg-Al (hcp-fcc) alloys , Dendrites tend to grow preferentially in the direction of <1120> or <2245> In Mg-Sn (hcp-bct) alloys, equiaxed dendrites grow along <1120> and basal <112X> (X≈2) direction to form an 18-branched structure, in the Mg-Zn (hcp-hcp) alloy , the preferred orientation of a-Mg dendrites will change continuously from <1120> direction to <1121> direction away from the basal plane with the increase of Zn content. In the transitional transitional region, hyperbranched algae branches The reason may be the anisotropy of the free energy of the solid / liquid interface induced by the introduction of high anisotropy Zn element.The results of the study reveal to some extent that the growth of a-Mg dendrite Morphology and branching structure of the magnesium alloy. At the same time, based on the rapid X-ray imaging technology, the 3D microstructure evolution in-situ characterization of the solidification process of magnesium alloy was first studied and the growth and evolution of the three-dimensional dendrite during the solidification of magnesium alloy was obtained.