Microstructural Tailoring of Ultrafine-Grained Magnesium Alloys for Lightweight Applications

航空航天和汽车工业对通过使用轻质材料如镁（Mg）和铝（Al）来减少重量、燃料消耗和温室气体排放的需求日益增加。此外，轻型材料，耐冲击负荷，需要在保护车辆和人员装甲，以防止受伤。镁（Mg）是最轻的金属，并且镁合金由于其低密度（~1738 kg/m3，~35% < Al）而被期望用于轻质应用。然而，镁合金由于其六方密排晶体结构而表现出较差的成形性、中等强度和有限的延展性。超细晶（UFG）材料（晶粒尺寸~ 1000 nm）具有上级粗晶材料的独特的微观结构相关性能。它们是通过晶粒细化生产的，具有增强的性能，如高强度和断裂韧性。强塑性变形（SPD）技术如高压扭转可用于生产具有优异强度、断裂韧性和延展性的块状UFG镁合金。在SPD期间，非常高的应变（真应变1）被施加在块体材料上，导致异常的晶粒细化，而不显著改变材料的总体尺寸。此外，大量的晶格缺陷，如晶界和位错的形成，改善材料的变形behaviors.This研究实现了一个协同的方法，涉及发展和全面的物理，机械和微观组织表征的UFG镁合金。将开发大块UFG镁合金，并将研究合金中超细晶粒和晶格缺陷结构演变过程中发生的机制。还将研究晶粒细化过程中发生的机制，它们对演变的显微组织和最佳加工条件的影响。UFG镁合金的动态力学性能，变形行为和损伤机制的特点是在中间（10-100 /s）到高应变速率（1000 /s）。将研究损伤累积的机制，包括应变局部化和ASB形成过程中发生的事件序列。本构方程和材料参数将被开发，以准确地描述性能和动态变形行为的UFG镁合金。全面的实验数据，本构方程和预测计算模型将是非常宝贵的定制轻质材料的性能，并为未来的轻质技术的创新发展的基础。此外，这项研究将培养在材料加工和表征方面具有特殊技能的高素质人才，包括汽车和航空航天行业雇主目前所需的电子显微镜和计算建模。

There is an increasing demand on the aerospace and automotive industries to reduce weight, fuel consumption and emission of greenhouse gases by using lightweight materials such as Magnesium (Mg) and Aluminum (Al). Also, lightweight materials, that are resistant to shock loading, are needed in protective vehicles and personnel armour to prevent injury. Magnesium (Mg) is the lightest metal and Mg alloys are desired for lightweight applications due to their low density (~1738 kg/m3, ~35% < Al). However, Mg alloys exhibit poor formability, moderate strength and limited ductility due to their hexagonal close-packed crystal structure. Ultrafine-grained (UFG) materials (grain sizes ~ 1000 nm) possess unique microstructure-dependent properties superior to coarse-grained materials. They are produced through grain refinement and have enhanced properties such as high strength and fracture toughness. Severe Plastic Deformation (SPD) techniques such as high pressure torsion can be used to produce bulk UFG Mg alloys with exceptional strength, fracture toughness and ductility. During SPD, very high strains (true strain 1) are imposed on a bulk material leading to exceptional grain refinement without significant change to the overall dimensions of the material. Also, large amounts of lattice defects such as grain boundaries and dislocations are formed that improve the deformation behavior of the materials.This research implements a synergistic approach involving the development and comprehensive physical, mechanical and microstructural characterization of UFG Mg alloys. Bulk UFG Mg alloys will be developed and mechanisms that occur during the evolution of ultrafine grains and lattice defect structures in the alloys will be studied. The mechanism/s that occur during grain refinement, their effect on the evolved microstructure and optimum processing conditions will also be studied. The dynamic mechanical properties, deformation behavior and mechanism of damage of UFG Mg alloys will be characterized at intermediate (10-100 /s) to high strain rates (1000 /s). Mechanisms that govern damage accumulation including the sequence of events that occur during strain localization and formation of ASBs will be studied. Constitutive equations and material parameters to accurately describe the properties and dynamic deformation behavior of the UFG Mg alloys will be developed.The comprehensive experimental data, constitutive equations and predictive computational models will be invaluable in tailoring the properties of lightweight materials and form the basis for future innovative developments in lightweight technologies. In addition, this research will train highly qualified personnel with exceptional skills in material processing and characterization including electron microscopy and computational modeling currently needed by employers in the automotive and aerospace industries.