【摘要】 镁及其合金具有低密度、高比强度、高导热性、高阻尼性以及良好的电磁屏蔽性能等优点,成为最具应用前景的结构材料之一。随着环保问题的日益突出,轻量化和节能减排变得日趋重要,对具有低密度、高性能和可回收再生产等特性的结构材料提出了大量且迫切的需求,这对镁合金的发展和应用提供了广阔的前景,但目前镁合金特别是变形镁合金还没能大规模工业化应用,还有问题需要解决。绝对强度较低、塑性较差等是影响变形镁合金应用的主要瓶颈。在材料传统的四种强化理论中,析出强化、加工硬化等可以显著提高变形镁合金的绝对强度,但同时会损害其塑性;固溶强化一般只能提高强度,降低塑性,在镁合金中虽存在一些能够同时提升强度和塑性的固溶元素,但该类元素较少,且对强度和塑性的提升效果也十分有限,还有待进一步研究发展;而晶粒细化是目前最有效的能同时提高材料强度和塑性的方法,当晶粒细化至数个微米量级时(超细晶),材料的强度和塑性会得到极大提升。在钢铁材料中的超细晶钢,就是利用超细晶组织(一般认为超细晶组织的目标是将晶粒尺寸从传统的几十微米细化至1～2μm)使钢铁材料的综合力学性能翻一番。同时,晶粒超细化也是高性能镁合金的研究重点之一。近期相关研究表明,超细晶镁合金拥有良好的强度和塑性,甚至还具有室温超塑性。目前常用于制备超细晶镁合金的方法主要有两种:剧烈变形法和中低温变形法。其中剧烈变形法主要采用等通道挤压、高压扭转、累积叠轧、多向锻造、粉末冶金等工艺方法来实现晶粒超细晶化,已有一定的发展历史,具有较深的研究基础;而中低温变形法是近年来新兴的一种制备超细晶镁合金的方法,同样能够成功制备出平均晶粒尺寸约为1μm的超细晶镁合金材料,该方法具备工业化应用的潜力。此外,通过剧烈变形法和中低温变形法制备的不同合金成分的超细晶镁合金材料性能差异较大,因此合金的成分设计在两种制备超细晶镁合金的方法中也具有至关重要的作用。总地来说,通过设计不同的合金成分,改进制备工艺,准确调控变形过程中的再结晶行为,制备出组织良好、性能优异的镁合金材料已成为发展超细晶镁合金的重要方向。因此,本文综述了目前超细晶镁合金的研究现状及主流的制备方法的优缺点,并分析了超细晶镁合金的制备方法和合金设计对组织和性能的影响,最后对超细晶镁合金的发展方向进行展望。更多还原

【Abstract】 Magnesium and its alloys have become one of the most promising structural materials,thanks to their superiority in low density,high specific strength,high thermal conductivity,high damping and good electromagnetic shielding performance. As the rising environmental problems,there is a increasingly pressing need for light-weight products,energy conservation and emission reduction. Especially,it has become an urgent and widespread demand for structural materials with low density,high performance and recyclable remanufacturing properties,which provides a broad prospect for the development and application of magnesium alloys. Nevertheless,magnesium alloys especially the wrought magnesium alloys haven’t achieved a large-scale industrial application yet,and still remain some issues to be solved.The key bottlenecks that affecting the application of wrought magnesium alloys lie in their low absolute strength and poor plasticity. In the four traditional reinforcement theories,precipitation strengthening,processing hardening can significantly enhance the absolute strength,yet accompanied by further deterioration of plasticity. Generally,solution strengthening is an effective approach to enhance strength,but also do harm to the ductility. Few solid solution elements are found to simultaneously contribute to strength and ductility,and the improvement of solid solution elements on strength and ductility is not satisfactory as well,hence further studied and exploration are still needed. Currently,grain refinement has been proved to be the most effective means for improving both strength and plasticity. The strength and ductility of materials will be significant boosted when the grain size is refined to several microns. In ultra-fine grained steel,it is generally believed that the goal of ultra-fine grained structure is to refine the grain size from dozens of microns to achieve the fine structure of 1—2 μm. In iron and steel materials,the properties of materials can be doubled by using ultrafine grained structure. Accordingly,grain refinement is also one of the focuses of high-performance magnesium alloys. Recent studies have shown that ultrafine grained magnesium alloys also possess favorable strength,plasticity and even low temperature super plasticity. At present,two approaches commonly used for preparing ultrafine grained magnesium alloys are severe deformation and mediumlow temperature deformation. The former primarily employs techniques like equal channel extrusion,high pressure torsion,cumulative rolling,multidirectional forging and powder metallurgy to achieve ultra-fine crystallization of grains,which holds a development history and a relatively deep research foundation. The latter is an emerging approach for preparing ultrafine grained magnesium alloys. The ultrafine magnesium alloys with an average grain size about 1 μm can also be successfully obtained,exhibiting a great potential for industrial application. Besides,there are significant difference in the properties of ultrafine grained magnesium alloys with diverse alloy components prepared by severe deformation and medium-low temperature deformation. Therefore,the composition design of alloys also plays a crucial role in preparation of ultrafine grained magnesium alloys in anyone of the approaches. Generally speaking,the leading direction of research on ultrafine magnesium alloys focus on designing various alloy components,optimizing the preparation process,regulating the recrystallization behavior during deformation,and preparing ultrafine magnesium alloys with satisfactory microstructure and excellent performance.In this paper,we review the current status and the preparation approaches of ultrafine grained magnesium alloys with their merits and drawbacks,and analyze the effect of preparation approach and alloy design on microstructure and properties of ultrafine grained magnesium alloys. Finally,we point out the development direction of ultrafine grained magnesium alloys in the future.更多还原