Manufacturing of High Strength, High Ductility, Rare Earth-Free Magnesium Alloy Plate and Sheet Materials by Differential Speed Rolling

该奖项支持美国制造业需求、工业和未来劳动力。镁合金具有轻质、强度、铸造性和阻尼能力，为运输、装甲、生物医学等领域的轻量化应用提供了重要机会。使用镁合金作为轻量化结构材料是克服节能挑战的最有效途径之一。金属薄板是在汽车、航空航天和消费品等许多工业中使用最多的金属合金形式之一。金属板材通常是用轧制技术制造的。然而，由于镁的晶体结构，用传统的轧制方法制成的金属板在室温成型时易碎且强度低，从而限制了它们的使用。为了释放镁合金的潜力，有必要提高其成形性。该项目通过一体化合金设计和加工来满足这一需求，重点是差速轧制，其中轧机的两个轧辊以不同的预定速度运行。该方法证明了生产高强度、高延展性和良好成形性的镁板和镁片的能力。研究涉及材料工程与加工、材料力学和先进制造等多个学科。这种融合的方法有助于促进多样性和包容性文化，并促进制造业的劳动力发展。差速轧制（DSR）是指两台轧辊以不同的速度轧制，生产出的镁合金板和薄板的织构以轧制方向倾斜的基面取向为主。这种织构变化导致基底滑移的强烈激活，从而导致更高的断裂应变。DSR通过提供额外的可控剪切应力，通过动态再结晶增强动态析出和晶粒细化，从而提高镁合金的强度和延展性，从而改进了传统的轧制工艺。与其他基于严重剪切变形的热机械加工技术（如等道角挤压和高压扭转）相比，DSR由于其连续性而具有可扩展性。然而，人们对合金成分、初始组织、轧制参数、最终组织（晶粒细化、析出相、织构）和加工合金的热机械性能之间的关系，以及对其温至室温成形性的适当轧制策略缺乏了解。该团队计划通过有限元模拟（FE-DEFORM）对轧制过程中的塑性变形进行实验研究。本研究旨在确定动态再结晶、动态析出、孪生、织构演化和晶粒生长在加工-显微组织-性能关系中的作用，从而发现改善镁合金成形性和增加应变硬化的新方法。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This award supports US manufacturing needs, industries and future workforce. With its lightness, strength, castability and damping capacity, magnesium alloys offer significant opportunities for lightweight applications in transportation, armor, biomedical and others. The use of magnesium alloys as lightweight structural materials is one of the most effective ways to overcome the challenges in energy conservation. Sheet metal is one of the most used forms of metal alloys in many industries such as automobile, aerospace, and consumer goods. Sheet metals are typically manufactured with rolling technology. However, due to the crystal structure of magnesium, sheet metals made with conventional rolling are brittle and low in strength for warm-to-room temperature forming thereby limiting their use. To unleash the potential of magnesium alloys, there is a need to improve their formability. This project meets this need through integrated alloy design and processing with focus on differential speed rolling in which the two rolls of a rolling mill run at different, predetermined speeds. This approach demonstrates a capability to produce magnesium plate and sheet with high strength and high ductility, and good formability. The research involves several disciplines including materials engineering and processing, mechanics of materials and advanced manufacturing. This convergent approach helps promote diversity and culture of inclusion as well as facilitates workforce development in manufacturing.Differential speed rolling (DSR) in which two rolls of a rolling mill run at distinct speeds can produce Mg alloy plates and sheets with textures dominated by basal plane orientations tilted in the rolling direction. This texture change leads to strong activation of basal slip and thus to higher fracture strains. DSR advances conventional rolling by providing additional controllable shear stresses which enhance dynamic precipitation and grain refinement via dynamic recrystallization leading to higher strength and ductility of Mg alloys. Compared to other thermomechanical processing technologies based on severe shear deformation, such as, equal channel angular extrusion and high-pressure torsion, DSR is scalable due to its continuous nature. However, there is a lack of understanding of the relationships between alloy composition, initial microstructure, rolling parameters, final microstructure (grain refinement, precipitates, texture) and thermomechanical properties of the processed alloys, and the appropriate rolling strategy for their warm-to-room-temperature formability. The team plans to perform experimental investigations driven by finite element simulations (FE-DEFORM) of plastic deformation in the rolling process. This research is expected to define the role of dynamic recrystallization, dynamic precipitation, twinning, texture evolution and grain growth in processing-microstructure-property relationships that lead to discovery of new approaches to improve formability and increase strain-hardening of Mg alloys.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.