Microstructural Tailoring of Ultrafine-Grained Magnesium Alloys for Lightweight Applications

航空航天和汽车工业越来越需要通过使用镁(Mg)和铝(Al)等轻质材料来减少重量、燃料消耗和温室气体排放。此外，防护车和人员装甲中还需要能够抵抗冲击载荷的轻质材料，以防止受伤。镁是最轻的金属，镁合金密度低(~1738 kg/m~3，~35%&lt；Al)，是轻量化应用的理想选择。然而，镁合金的六方密排晶体结构使其具有较差的成形性、中等的强度和有限的塑性。 超细晶(UFG)材料(晶粒度约为1000 nm)具有独特的微结构特性，优于粗晶材料。它们是通过细化颗粒而产生的，并具有高强度和断裂韧性等增强性能。高压扭转等严重塑性变形(SPD)技术可用于生产具有优异强度、断裂韧性和延展性的块体UFG镁合金。在SPD过程中，对块状材料施加非常高的应变(真实应变1)，从而在不显著改变材料整体尺寸的情况下实现特殊的晶粒细化。此外，大量晶格缺陷的形成，如晶界和位错，改善了材料的变形行为。 这项研究采用了一种协同的方法，涉及UFG镁合金的开发和全面的物理、机械和微观结构表征。将开发块体超细晶镁合金，并研究合金中超细晶和晶格缺陷结构演变的机制。还将研究细化过程中的机理/S及其对组织演变的影响和最佳工艺条件。超细晶镁合金的动态力学性能、变形行为和损伤机制将在中应变率(10-100/S)到高应变率(1000/S)下进行表征。将研究支配损伤积累的机制，包括在菌株本地化和ASBS形成期间发生的事件序列。建立了能够准确描述超细晶镁合金性能和动态变形行为的本构方程和材料参数。 全面的实验数据、本构方程和预测计算模型将在定制轻质材料的性能方面具有无价的价值，并为未来轻质技术的创新发展奠定基础。此外，这项研究将培训在材料加工和表征方面具有特殊技能的高素质人员，包括汽车和航空航天行业雇主目前需要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.