GOALI:Deformation Mechanisms and Microstructure Evolution in Thermo-Mechanical Processing of Mg Alloys for Structural Automotive Applications

技术概要：虽然人们已经广泛观察到，变形孪晶在室温和高温下的镁合金的变形响应中起着主导作用，但其对这些合金的延展性的确切作用还不清楚。在镁合金中建立潜在变形机制的物理学已经被许多因素复杂化，包括（i）在镁合金中观察到的两类变形孪晶之间的显著形态和应变硬化速率差异，（ii）晶粒尺寸和温度对变形孪晶程度的强烈影响，（iii）高温塑性变形过程中动态再结晶的激活，（iv）某些粗晶镁合金在一定温度范围内旋转动态再结晶的激活，以及（v）拉伸孪晶和收缩孪晶对再结晶过程的潜在不同影响。建议进行详细的实验和建模研究，以定量地了解两种特定镁合金：AZ 31和Mg-0.2wt%Ce在热机械加工中的潜在变形机制。实验研究将包括室温和高温简单压缩试验，这些试验将被中断，以便使用取向图像显微镜进行详细的微观结构研究，并测量塑性变形样品中晶粒尺度的局部储能。还建议开发和验证新的基于物理的弹粘塑性晶体塑性模型，以预测这些合金的热机械变形中的各向异性应力-应变响应和微观结构的演变。这些模型随后将用于开发新的工艺路线，以经济高效地制造由镁合金制成的汽车结构部件。非技术总结：强度高但重量轻的镁（Mg）合金具有巨大的潜力，可大幅提高汽车的燃油效率，并相应减少汽车二氧化碳排放。这些合金广泛应用的主要障碍是它们非常有限的室温延展性，这妨碍了通过标准的廉价锻造加工方法成功制造所需的汽车结构部件。该提案旨在产生镁合金结构的基本物理数据集和计算模型，这些数据集和计算模型是找到改善这些合金的室温延展性的方法所需要的。德雷克塞尔大学和通用汽车全球研发中心的研究人员之间拟议的跨学科合作将为汽车工业开发更好的镁合金，并可能对具有类似晶体结构的其他金属的加工产生影响。该项目将产生两名精通跨学科研究的博士学位，涉及新型材料表征技术，高级计算力学和应用数学。该项目将使众多国内本科生和研究生，特别是科学和工程领域代表性不足的群体的成员，接触到尖端的研究方法和设备。

TECHNICAL SUMMARY: Although it has been widely observed that deformation twinning plays a dominant role in the deformation response of Mg alloys at room and elevated temperatures, its precise role on the ductility of these alloys is not yet understood. Establishing the physics of the underlying deformation mechanisms in Mg alloys has been complicated by many factors, including (i) the dramatic morphological and strain hardening rate differences between the two families of deformation twins observed in Mg alloys, (ii) the strong influence of grain size and temperature on the extent of deformation twinning, (iii) the activation of dynamic recrystallization during plastic deformation at elevated temperature, (iv) the activation of rotational dynamic recrystallization in some coarse-grained Mg alloys in certain temperature ranges, and (v) the potentially different influences of extension and contraction twins on the recrystallization processes. It is proposed to undertake a detailed experimental and modeling study to develop quantitative insights into the underlying deformation mechanisms in thermo-mechanical processing of two specific Mg alloys: AZ31 and Mg-0.2wt% Ce. Experimental investigations will include room and high temperature simple compression tests which will be interrupted for detailed microstructure investigations using orientation image microscopy and measurements of the local stored energy at the grain scale in plastically deformed samples. It is also proposed to develop and validate new physics-based elastic-viscoplastic crystal plasticity models to predict the anisotropic stress-strain response and the evolution of the microstructure in thermo-mechanical deformation of these alloys. These models will be subsequently employed to develop novel processing routes for cost-effective manufacture of structural automotive parts made from Mg alloys.NON-TECHNICAL SUMMARY: Strong but light magnesium (Mg) alloys offer tremendous potential for dramatic increases in the fuel efficiency of automobiles, with corresponding reductions in automotive CO2 emissions. The primary impediment to widespread application of these alloys is their very limited room temperature ductility, which prevents successful manufacture of the desired automotive structural components by standard inexpensive wrought processing methods. This proposal aims to produce the fundamental physical data sets and computational models of Mg alloy structure which are needed to find ways to improve the room temperature ductility of these alloys. The proposed interdisciplinary collaboration between researchers at Drexel University and at the General Motors Global R&D Center will result in the development of better Mg alloys for the automotive industry and may also have implications for the processing of other metals with similar crystalline structures. This project will produce two PhDs skilled in interdisciplinary research involving novel material characterization techniques, advanced computational mechanics, and applied mathematics. The project will expose numerous domestic undergraduate and graduate students, especially members of underrepresented groups in science and engineering, to cutting edge research methodologies and equipment.