高性能镁合金研究及应用的新进展

镁合金作为21世纪的绿色环保工程材料之一,近年来已成为全球学术界的一个研究热点,并越来越受到工业界的重视。主要综述了高性能镁合金的研究进展和应用现状,主要介绍了阻燃镁合金、低成本高强度铸造镁合金以及高强高韧高温变形镁合金研究及应用的新进展。此外,还介绍了镁合金成形加工技术方面的研究成果。最后,展望了高性能镁合金的发展趋势。     

镁及镁合金功能材料的研究进展

镁及镁合金质轻、比强度、比刚度高,在交通运输、航空航天等行业有着广泛的应用。随着对镁合金研究的深入,镁合金越来越多的性能被开发和利用。本文综述了镁及镁合金作为阻尼材料、导热材料、电磁屏蔽材料、生物医用材料、储氢材料和电池材料的优缺点及研究现状,并阐述了改善和提高各种性能的方法,讨论了未来的主要研究方向。     

超细晶镁合金的研究现状及展望

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。     

镁合金在大变形和高应变率下塑性变形研究进展

介绍了强应变塑性大变形下镁合金研究现状.重点综述了在较高应变率及冲击载荷作用下关于镁合金变形的研究情况,同时也比较详细地综述了在不同温度、不同载荷作用下镁合金塑性变形特征及其物理机制.最后简要介绍了几个描述材料在较高应变率和冲击载荷作用下变形行为的数学表示式,并就镁合金作为结构材料的研究说明了作者的一些看法.     

难变形材料热静液挤压复合精密塑性成形工艺

目的 研究热静液挤压及其复合塑性变形工艺在高密度钨合金、钨铜合金、钛基复合材料及镁合金薄壁细管等难变形材料方面的制备。方法 通过对高密度钨合金难变形材料进行热静液挤压及旋转锻造等塑性成形,分析了材料在成形过程中的微观组织及性能变化规律和强化机制,制备出大长径比穿甲弹弹芯材料。在此基础上,将该复合塑性变形技术拓展至两相不互溶材料钨铜合金、钛基复合材料及大长径比镁合金毛细管等难变形材料方面的制备。结果 热静液挤压及其复合塑性变形工艺在粉末冶金难变形材料的致密化方面具有显著优势,获得材料不仅致密度高,而且有效实现了控形控性;对于镁合金薄壁细管成形而言,也可以实现组织与性能的有效调配,同时材料的精度较高。结论 热静液挤压及其复合塑性变形工艺在难变形材料的制备与成形方面具有独特的优势与广阔的应用前景。     

变形镁合金的研究现状

镁合金将成为21世纪最重要的商用轻质结构材料。本文综述了变形镁合金的研究现状，介绍了改善镁合金塑性变形能力的途径。     

稀土变形镁合金的研究和开发

论述了国内外稀土变形镁合金的研究和开发现状,分析了在变形镁合金中添加稀土元素所起的作用以及稀土对合金组织、性能及变形加工能力所产生的影响,总结了稀土变形镁合金中准晶相的形成、作用及研究特点,讨论了稀土变形镁舍金研究和开发中存在的问题和困难,指出稀土变形镁合金是镁合金开发应用中的一个重要发展方向.     

变形镁合金连续铸轧技术研究进展

变形镁合金材料具有良好的综合性能而被广泛应用,但由于其常温塑性较差导致变形镁合金材的加工变形困难.连续铸轧技术是一种短流程、近终成型板坯加工技术.综述了变形镁合金的合金体系、变形特点、加工方式和连续铸轧技术的工艺特点,探讨了变形镁合金连续铸轧技术的可行性,并介绍分析了国内外有关变形镁合金连续铸轧技术的研究现状和发展前景.     

变形镁合金成形工艺研究及其应用

变形镁合金塑性加工是目前镁合金研究的前沿领域.综述了变形镁合金主要的成形工艺方法及应用领域,介绍了变形镁合金挤压、轧制、锻造、冲压、超塑变形等变形工艺的特点和关键;展望了变形镁合金的应用发展,指出了其成形工艺在军工、汽车、电子、航空航天等领域具有越来越广阔的应用前景.     

镁合金 AZ40M 再结晶晶粒尺寸与硬度模型研究

目的研究变形温度及变形速率对镁合金AZ40M再结晶晶粒尺寸以及硬度的影响。方法在gleeble-1500D热模拟机上进行热物理模拟压缩实验,变形温度为250~400℃,变形速率为0.001~1 s-1,通过金相法观测AZ40M镁合金在不同变形条件下的组织形貌,采用维氏硬度计测出镁合金热变形后的硬度值。结果当升高变形温度或降低变形速率时,材料的晶粒尺寸增大且硬度减小。结论得出了再结晶晶粒尺寸的变化规律,建立了AZ40M镁合金的晶粒尺寸与硬度的关系模型。     

超高强韧Mg-Gd-Y-Zn-Zr变形镁合金研究进展

超高强韧镁合金的研发对推广镁合金在高技术领域的应用具有重要意义。镁与稀土均是我国的优势资源,因此在我国发展超高强韧稀土镁合金具有得天独厚的优势,其中Mg-Gd-Y-Zn-Zr系变形镁合金因其接近高强铝合金的超高强度和塑性,近年来受到研究者的广泛关注。综述了超高强韧Mg-Gd-Y-Zn-Zr系变形镁合金的合金成分、常规塑性变形工艺、新型剧烈塑性变形工艺和热处理工艺对该合金显微组织和力学性能的影响规律,以及该超高强韧变形镁合金的显微组织特征和强韧化机理。T5峰时效态超高强韧Mg-8.2Gd-3.8Y-1Zn-0.4Zr(质量分数)挤压合金具有双峰分布的晶粒尺寸“软-硬”复合层片微结构,以及由高密度的基面γ′纳米片状析出相和棱柱面β′纳米析出相形成的近连续网状结构,该挤压合金室温拉伸屈服强度、拉伸强度和断裂延伸率分别为466 MPa、514 MPa和14.5%。介绍了哈尔滨工业大学等单位在超高强韧Mg-Gd-Y-Zn-Zr系变形镁合金的规模化制备和应用方面的研究进展,并展望了Mg-Gd-Y-Zn-Zr系变形镁合金的发展趋势。     

液态模锻材料及其研究进展

液态模锻作为一种精密成型技术应用范围不断扩大,液锻件正在不断替代普通铸件和固态锻件用于各行各业。但液态模锻的材料范围不够明晰,导致铸造合金液态模锻研究与应用很多,而各种变形合金的液态模锻却鲜有报道。如果定义适于液态模锻技术成型的材料统称为液态模锻材料,并用流变充型能力、流变补缩能力以及开裂敏感性定量表征液锻材料的工艺性能,则各种合金钢、球墨铸铁、铝合金、镁合金、锌合金、铜合金、生物材料及金属基复合材料都属于液锻材料,且都具有较好的液锻工艺性能。目前只有液锻铝合金、液锻镁合金、液锻锌合金和一些液锻合金钢研究应用活跃,并取得了工业应用。建议今后加强液锻材料的工艺性能预报、变形合金特别是宽结晶温度范围合金的液态模锻以及金属基复合材料的研究开发。     

细晶变形镁合金的研究进展

综述了变形镁合金的种类、基本变形特性和优良性能,介绍了轧制、挤压、锻造、超塑成形等常用成形技术,探讨了变形镁合金晶粒细化的机理及常用方法如等径角挤压、形变热处理等,阐述了变形镁合金的研究现状、存在的问题,并指出了未来变形镁合金研究开发的方向.     

Microstructural evolution and tensile mechanical properties of thixoforged ZK60-Y magnesium alloys produced by two different routes

Semi-solid processing of magnesium alloys is generally based on conventional magnesium-based casting alloys such as Mg–Al series. However, these casting alloys do not give such high mechanical properties as the alloys that are conventionally wrought such as Mg–Zn series. In this paper, a ZK60 magnesium alloy with the addition of Y was thixoforged. The semi-solid thermal transformation (SSTT) route and the recrystallisation and partial melting (RAP) route were used to obtain the semi-solid feedstocks for thixoforging. Microstructural evolution during partial remelting was studied at temperatures for times. Tensile mechanical properties of thixoforged components at room temperature were examined. Results show that a fine spheroidal microstructure can be obtained by the RAP route. Compared to the RAP route, the SSTT alloy shows coarsened solid grains with a relatively high proportion of intragranular liquid droplets. With prolonged holding time, the solid grain sizes of the SSTT alloy and the RAP alloy increased. Coalescence was dominant in the SSTT alloy and Ostwald ripening was dominant in the RAP alloy. Thixoforging for the SSTT alloy and the RAP alloy resulted in successful filling of the die. The tensile properties of the thixoforged RAP alloy were satisfactory and exceeded those of the thixoforged SSTT alloy. However, the mechanical properties of both the thixoforged SSTT alloy and the thixoforged RAP alloy decreased with prolonged holding time.     

Magnesium – der Zukunftswerkstoff für die Automobilindustrie?

Magnesium – future material for automotive industry? Magnesium alloys show a very high potential in automotive applications as constructive metal, whereas the main focus lies on die cast parts. Electronic industry is the major commercial consumer for die castings besides the automobile industry. Room temperature applications like steering wheels and frame components in cars as well as mobile phone‐ or notebook housings are well established. These castings are produced with AZ‐ or AM‐magnesium alloys, which show good room temperature properties and a good castability. The great alloy development challenge in extending the use of magnesium cast alloys are application for higher temperatures. The application in powertrain components is considered to be the benchmark here. Besides alloy development there are also further research activities in development of casting processes. Semi‐solid processes like New‐Rheocasting (NRC), Thoxomolding ? or Thixocasting (TC) are adapted to the requirements of newly developed alloys. Not only cast alloys but also magnesium wrought alloys have moved to the centre of interest in the last decade. Alloy development for improving the formability on the one hand as well as process development in extrusion or rolling has to be done in order to find optimum parameters for deforming magnesium alloys properly.     

变形镁合金塑性的改善

塑性差已成为变形镁合金加工与应用上的一个瓶颈,改善变形镁合金的塑性也就成为变形镁合金研究与应用中急需解决的关键技术之一.细化晶粒、控制织构、激活非基面滑移系可以显著改善镁合金的塑性,是较有前景的塑性改善方法.从以上3方面综述了变形镁合金塑性改善的最新研究进展.     

Grain size effects on the mechanical properties of some squeeze cast light alloys

Mechanical property-grain size relationships have been examined for squeeze cast Al-4.5% Cu alloy, for an aluminium alloy with a composition corresponding to wrought 7010, and for a magnesium alloy AZ91. The general trend of the results obtained showed that the tensile properties and the fatigue strength improved as grain size decreased and the reverse was found to be the case for the fatigue crack propagation resistance and fracture energy of these castings. However, the results also showed that no simple common relationship existed between grain size and the tensile properties of the different alloys. The results are discussed in respect of their microstructures.     

AZ80 and ZC71/SiC/12p closed die forgings for automotive applications: technical and economic assessment of possible mass production

Abstract

In this study, redesigning for equal functional properties and rapid prototyping of hot forged automotive parts based on commercially available wrought magnesium alloys (AZ80) and composites (AZ80/SiC/12p) were performed. To achieve the same functional properties in a forged automotive component irrespective of the structural material selected, an automotive connecting rod, mass produced in aluminium alloy 6061, was redesigned to use wrought magnesium alloy (AZ80A) and particle reinforced magnesium alloy matrix composite (ZC71/SiC/12p). By applying conventional hot forging technology, prototype connecting rods were forged, trimmed, and heat-treated on a semiindustrial scale. The microstructure of both as extruded and hot forged specimens was examined and the tensile properties of AZ80, ZC71/SiC/12p, 6061 and 6061/SiC/15p test bars machined from hot forged connecting rods were measured. Weight reduction in the redesigned connecting rods was determined and the substitution of magnesium and aluminium based materials for steel was compared in terms of cost.     

A comparison of the deformation of magnesium alloys with aluminium and steel in tension, bending and buckling

A comparison was made between high pressure die cast and wrought magnesium alloys and formed mild steel and aluminium in tensile, bending and buckling deformation. It was found that the energy absorption properties of magnesium alloys were particularly good in bending and buckling, absorbing up to 50% more energy than the aluminium and over 10 times more energy than the mild steel. The primary reason for the good performance of Mg alloys was that the low density means that sections of increased thickness can be made without increasing weight. This is particularly beneficial in bending as the strength of a section in bending is proportional to the square of the thickness. However, it was also observed that the high rate of work hardening of Mg alloys is particularly important and this allows for considerably more energy to be absorbed. A simple analytical strut buckling model has been modified to incorporate work hardening and a good correlation has been observed between this model and the experimental results.