GOALI: Computational Materials Science Approach to Study Precipitation-Hardening Magnesium-Zinc-Rare Earth (Mg-Zn-RE) Alloys

技术概述：提出了研究Mg-Zn-RE（稀土：Nd， Ce, Sm）合金的相平衡和力学性能的方法。发现锌的加入为类似于铝铜合金中GP区形成的热处理提供了一条途径。结果表明，稀土元素的添加显著提高了机械性能，但到目前为止，大多数研究都是通过反复试验。本研究采用计算材料设计方法对Mg-Zn-Nd（Ce, Sm）合金进行优化，使其在制造（铸造和挤压）和热处理条件下的力学性能达到最佳组合。提出的研究(1)产生了Mg-Zn-Nd（Ce, Sm）体系的热力学描述；(2)根据获得的相图，对具有代表性的合金进行定向凝固，表征形成的相的组织和成分以及凝固后的显微组织；(3)测定所选合金在凝固状态和经过特殊热处理后的力学性能。整体力学性能（屈服强度，极限抗拉强度，硬度，延展性）表征。纳米压痕将用于将整体性能与微观尺度上进行的工艺联系起来，并检查各个相的机械性能。本研究的智力优势在于利用计算热力学与关键实验相结合，快速获得Mg-Zn-RE的热力学描述。这种方法不同于传统的仅仅依靠实验的方法，传统的方法对于多组件系统来说既繁琐又无效。获得的热力学描述可用于提供适当的热力学量，作为动力学模型的输入，用于预测微观结构，并最终预测力学性能。非技术总结：镁是最轻的结构金属，世界各地的研究人员都受到提高燃料经济性和减少环境影响的前景的激励，开发镁合金以取代汽车应用中的钢和铝。为了实现这一目标，本研究使用计算热力学方法开发了一类新的有前途的镁锌稀土（Nd, Ce, Sm）合金，这种方法比以前实现的更有效和准确。合金的机械性能（强度）将与合金内部相的微纳米级性能进行测试，因此所获得的知识将有助于更好地了解其他类型合金的未来发展。这项工作涉及威斯康星大学和通用汽车公司的研究人员之间的合作。提议的工作的更广泛的影响包括为年轻人——未来的科学家和工程师——提供一个机会，让他们在工业界和学术界顾问的监督下，体验研究一个广泛的、具有学术和工业重要性的基本问题。学生们将获得在工业环境中进行部分研究的宝贵经验，例如在通用汽车研发中心。

TECHNICAL SUMMARY: It is proposed to study phase equilibria and mechanical properties in Mg-Zn-RE (rare earth: Nd, Ce, Sm) alloys. Zn additions were found to provide an avenue for heat treatment analogous to GP zone formation in Al-Cu alloys. Results have shown that RE additions dramatically improve mechanical properties, but most research so far has been by trial and error. The proposed study adopts a computational materials design approach to optimize Mg-Zn-Nd(Ce, Sm) alloys for the best combination of mechanical properties in the as-fabricated (cast and extruded) and heat-treated conditions. The proposed study (1) produces thermodynamic descriptions of the Mg-Zn-Nd(Ce, Sm) systems; (2) carries out directional solidification of representative alloys to characterize structures and compositions of the phases formed and solidified microstructures, in the context of the phase diagrams obtained; (3) measures the mechanical properties of selected alloys in the solidified state and after specific thermal treatment. Bulk mechanical properties (yield strength, ultimate tensile strength, hardness, ductility) are characterized. Nanoindentation will be used to relate bulk properties to processes going on at the micro-scale and to examine the mechanical properties of the individual phases. The intellectual merit of this research includes the use of computational thermodynamics coupled with key experiments to rapidly obtain thermodynamic descriptions of Mg-Zn-RE. This approach differs from traditional ones that rely only on experiments, which are tedious and ineffective for multi-component systems. The thermodynamic descriptions obtained can be used to provide appropriate thermodynamic quantities as input for kinetic models, for predicting microstructures and, ultimately, mechanical properties.NON-TECHNICAL SUMMARY: Magnesium is the lightest structural metal, and researchers worldwide are motivated by the promise of improved fuel economy and reduced environmental impact to develop magnesium alloys for replacing steel and aluminum in automotive applications. To address this goal the present research uses a computational thermodynamics approach to develop a new class of promising magnesium-zinc-rare earth (Nd, Ce, Sm) alloys in a manner that is more efficient and accurate than has been achieved previously. The mechanical properties (strength) of the alloys will be tested against the micro- and nanoscale properties of the phases inside the alloys, so that the knowledge gained will lead to better understanding for future development of other kinds of alloys. This work involves collaboration among researchers from the University of Wisconsin and General Motors. The broader impact of the proposed work includes an opportunity for young people - future scientists and engineers - to experience working on a broad, fundamental problem with both academic and industrial importance and under the supervision of both industrial and academic advisors. The students will gain the invaluable experience of working on a portion of their research in an industrial environment, i.e. at the General Motors R&D Center.