The role of composition control on the structure property relationships in Mg-Nd-Zn alloys

镁合金是重量关键型应用的理想选择，其中重量的减少与能耗的减少相关。然而，商业上可行的镁合金的性能特征不足以满足许多设想的应用。通过控制合金成分和第二相的分布来设计镁合金对于实现这些合金的全部潜力是重要的。据报道，在Mg-RE合金（RE=稀土）中添加Zn导致显微组织的改性，并且在相对低的RE含量下产生机械性能。然而，目前只有稀土添加剂与高溶解度的镁，如Gd和Y，已被系统地研究，以了解稀土：锌比的微观结构和所得的机械性能在一系列的加工条件下的作用。Nd是一种低成本和低溶解度的RE添加剂，其已显示通过形成有效阻碍Mg-Nd和Mg-Nd-RE合金中的塑性变形的细尺度颗粒来增强Mg合金的强度。预计Zn的存在将通过在相对较低的Nd含量下对微观结构的改性来提高机械性能，本研究的最终目标是通过对合金成分的改性和受控的热处理来开发具有可调机械性能的用于结构应用的低成本Mg合金系统。通过在晶界处沿着金属间化合物颗粒形成固态沉淀来设计微观结构和所得机械性能的能力，将允许开发具有增强的强度和延展性的协同组合的合金。Zn比率将被研究，以了解凝固过程中使用原位X-射线衍射的微观结构演变。射线衍射和随后的非原位电子显微镜。金属间相、它们的形成温度和它们的这些相的体积分数将用于改善目前可用的Mg-Nd-Zn相图的富Mg侧。在这种热处理过程中，要与电子显微镜的帮助下进行研究的作用，修改在凝固过程中形成的金属间相和新的固态析出物的形成。这将提供进一步的步骤，在该步骤期间，可以改变微观结构和所得的机械性能。将在室温和高温下评估铸造和热处理合金的机械性能，以了解合金成分、金属间相和热历史对这些性能的作用。

Mg alloys are ideal for weight critical applications, where the reduction in weight correlates with a reduction in energy consumption. However, the property profiles of commercially viable magnesium alloys are not sufficient of many of the applications envisaged. The design of Mg alloys through control of both the alloy composition and distribution of secondary phases is important in realizing the full potential of these alloys. It has been reported that the addition of Zn to Mg-RE alloys (RE=rare earth) results in modification of the microstructures and the resulting mechanical properties at relatively low RE content. However, to present only RE additions with high solubility in Mg, such as Gd and Y, has been investigated systematically to understand the role of RE:Zn ratio on the microstructure and resultant mechanical properties in a range of processing conditions. Nd is a lower cost and low solubility RE addition that has shown to enhance the strength of Mg alloys through formation of fine scale particles that hinder plastic deformation effectively in Mg-Nd and Mg-Nd-RE alloys. It is expected that the presence of Zn will enhance the mechanical properties through the modification of microstructure at a relatively low Nd content.The ultimate goal of this investigation is to develop a lower cost Mg alloy system for structural applications with tunable mechanical properties through modification of the alloy composition and controlled heat treatments. The ability to design the microstructure and resultant mechanical properties through formation of solid-state precipitation along with intermetallic particles at the grain boundaries and would allow the development of alloys with a synergistic combination of enhanced strength and ductility.A range of alloys with varying Nd: Zn ratios will be investigated to understand the microstructural evolution during solidification using in situ X-ray diffraction and subsequent ex situ electron microscopy. The intermetallic phases, their formation temperature and their volume fraction of these phases will be used to improve the Mg rich side of the Mg-Nd-Zn phase diagram that is currently available. The role of heat treatments on modifying the intermetallic phases formed during solidification and formation of new solid-state precipitates during such heat treatments is to be investigated with the aid of electron microscopy. This would provide for a further step during which the microstructure and the resultant mechanical properties could be modified. The mechanical properties of the cast and the heat treated alloys will be evaluated both at room and at elevated temperature to understand the role of alloy composition, intermetallic phases and the thermal history on such properties.