脉冲电流对2091Al—Li合金超塑性及断裂行为的影响

研究了脉冲电流对2091 Al-Li合金在高速超塑变形时的力学行为及断裂机制的影响。结果表明:施加脉冲电流使2091 Al-Li合金在高应变速度(10~(-2)s~(-1))时仍具有较高的应力应变速度敏感指数和超塑性能。扫描电镜观察表明,施加脉冲电流使2091 Al-Li合金的断裂机制由晶界撕裂转变成典型的超塑断裂-在粒子及晶界处形成孔洞,相互连接以至断裂。     

Manufacturing advantages of superplastically formed fine-grain Ti-6Al-4V alloy

Superplastic forming (SPF) of Ti-6Al-4V has traditionally been performed at 900 °C. Although SPF equipment and dies have been developed to withstand this high temperature, their life is limited and maintenance is high. In addition, the formed sheets need chemical milling after processing to remove a significant layer of alpha case, and parts require hand polishing due to a rough die surface caused by high temperature oxidation. The recent development of a Ti-6Al-4V alloy with a grain size of around 1 μm has led to the possibility of superplastic forming at a much lower temperature than regular Ti-6Al-4V. In addition, the forming speed can be increased. This work looks at some of the SPF attributes of fine-grain titanium, in particular, the optimum forming temperature, the thinning characteristics, alpha case formation, and forming speeds. The authors also address manufacturing advantages, such as die life, equipment needs, and operator comfort. Some prototype and preproduction aircraft components on Boeing airplanes are presented. The results show that the new fine-grain material could significantly lower the cost of SPF Ti-6Al-4V part production for the aerospace industry. This paper was presented at the International Symposium on Superplasticity and Superplastic Forming, sponsored by the Manufacturing Critical Sector at the ASM International AeroMat 2004 Conference and Exposition, June 8–9, 2004, in Seattle, WA. The symposium was organized by Daniel G. Sanders, The Boeing Company.     

应变速率强化与应变强化的过程及其对比分析

本文用密栅云纹实验法显示和观测了具有应变速率强化效应与应变强化效应材料的应变产生、发展及传播过程,并对两种强化效应传播应变的能力进行了分析比较。     

Superplasticity of Mg-5.8Zn-1Y-Zr alloy sheet fabricated by combination of extrusion and hot-rolling processes

Superplastic behaviors of quasicrystal phase containing Mg-5.8Zn-1Y-0.48Zr alloy sheets fabricated by combination of extrusion and hot-rolling processes have been investigated at temperature ranging from 623 to 753 K and at the strain rates ranging from 10-4 to 10-2 s-1 by uniaxial tensile tests. An excellent superplasticity with the maximum elongation to failure of 1020% was obtained at 753 K and the strain rate of 1.04×10-3 s-1 and its strain rate sensitivity, m, is as high as up to 0.75. The microstructure was stable during superplastic deformation due to the uniformly distributed fine quasicrystal particles. In addition, micro-cavities and their coalescences were observed in the superplastic deformation of the ZW61 magnesium alloy. Grain boundary sliding (GBS) was considered to be the main deformation mechanism during the superplastic deformation. Dislocation creep controlled by atom diffusion through grain boundaries or interior grains is suggested mainly to accommodate the GBS in super-plastic deformation.     

Property and microstructure analysis of ZK60 alloy superplastic sheet

It was investigated that the superplastic mechanical properties of fine-grained ZK60 magnesium alloy sheets at the temperature range of 200-420 ℃ and strain rate range of 5.56 × 10-4 -5.56 ×10-2 s-1 by tensile tests.And the microstructure evolution during the superplastic deformation of ZK60 magnesium alloy was examined by metallurgical microscope and transmission electronic microscope (TEM).The results showed that fine-grained ZK60 magnesium alloy starts to exhibit superplasticity from 250 ℃ and the maximum elongation is about 1106% at 400 ℃ and 5.56 × 10-4 s-1.The strain rate sensitivity is significantly enhanced with the increase of temperature and with the decrease of strain rate.The predominate superplastic mechanism of ZK60 magnesium alloy is grain boundary slide (GBS) at the temperature range of 300-400 ℃.The grains of ZK60 alloy remain equaxial after superplastic deformation,and dynamic continuous recrystallization (DCRX) is an important softening mechanism and grain stability mechanism during the superplastic deformation of the alloy.The curved grain boundaries and crumpled bands at grain boundaries after deformation prove GBS generates during superplastic deformation of ZK60 magnesium alloy.     

Replica technique for the inspection and measurement of small internal screw threads

The superplastic behaviour of zinc-22% aluminium alloys can be utilized in the production of replicas of small internal screw threads. Reproduction of size is better than with epoxy resin, moulding rubber or plaster of Paris and the replica has sufficient hardness to enable a contact method of measurement to be used. The replica technique is described and examples of dimensional measurement and of the determination of surface finish parameters are presented.     

Fe3Al基合金用作结构材料的应用基础研究

研究了Fe-28Al-5Cr与Fe-28Al-5Cr-0.5Nb-0.1C合金的高温变形行为,发现温度在850℃左右,应变速率为8.33×10-4s-1时,呈现出大晶粒的超塑性变形行为,延伸率分别达到145%和254%.这意味着不需要获得细晶的特别工艺处理就可以直接进行超塑性成形.与传统细晶导致超塑性不同,其激活能分别为243kJ/mol和218kJ/mol,变形机理为位错运动而不是晶界滑动.在较低的应变速率及大约850℃下制备出壁厚为1.7～2mm,直径为50mm的薄壁管坯分别用电子束焊(EBW)及钨极氩弧焊(GTA)两种方法对厚度为2mm左右的Fe-Al基合金试样进行了可焊性及焊接工艺优化研究.电子束焊在真空中进行,集中的高能量输入使熔合区组织细化,可实现对Fe3Al基合金的焊接.采用钨极氩弧焊时,以中低碳铬钼钢为填充料,降低焊接电流和热输入,对焊件采用适当的预热、缓冷工艺,是焊接工艺优化的主要因素,应用可焊性及焊接工艺优化研究的结果,制备出相应尺寸的薄壁焊管.     

Effect of initial microstructure on superplastic deformation of AZ70 magnesium alloy

The mechanical properties and deformation mechanism of semi-continuously casting and as-extruded AZ70 magnesium alloys in a wide range of grain sizes(from 14 to 103μm)were investigated at 653 K and 1×10-3s -1.It is discovered that with reducing grain size,flow stress is weakened and plasticity is improved and even superplasticity exhibits.SEM and OM were used to clarify the deformation mechanism.It is suggested that dynamic recrystallization(DRX)is the coordination deformation mechanism of grain boundary sliding(GBS)for coarse grain,and cavity and intracrystalline slip are the coordination deformation mechanisms of GBS for fine grain.     

西北有色金属研究院钛合金研究进展

概述了西北有色金属研究院（NIN）研发的部分高温、高强、低成本、超塑性及低温钛合金近年来的研究进展。指出：使用温度在550～650℃之间的高温钛合金中，550℃高温钛合金已获得应用，Ti-600合金因室温和600℃下综合性能优异，尤其是极佳的蠕变性能，可以用做高推重比发动机压气机轮盘和叶片，具有较好的应用前景；在强度级别为1000～1600MPa的高强钛合金中，Ti—B20合金和Ti-1300合金适宜制作高强或超高强钛合金弹簧；低成本钛合金、超塑性温度较低且应变速率较高的超塑性钛合金、低温钛合金的研究从未间断过，某些合金也已得到应用；NIN今后研究重点是建立已研发合金的规范体系，降低其制造成本，提高其使用性能，最终使其获得广泛应用。