High strain-rate superplasticity in a fine-grained PM 7475 Al Alloy

Superplastic behavior of powder-metallurgy (PM) processed 7475 +0.7Zr Al alloy having a fine grain size of 2 um was investigated. Strain-rate-change tests were conducted at elevated temperatures to examine the strain rate-stress relations. The deformation behavior was analyzed by assuming the presence of threshold stress for grain boundary sliding. After the threshold-stress compensation, the plastic flow was found to correlated well with lattice self-diffusion in pure aluminum. A maximum tensile elongation of up to 1000% was observed at a very high strain rate near l0^-1s^-1 and 515°C. A deformation map was constructed to identify the dominant deformation mechanism for the PM alloy. It was the grain boundary sliding controlled by lattice diffusion in aluminum. Evidence of short fiber or whisker-like formation were observed on the fractured samples over a wide range of temperature.     

黑色金属模具复杂型腔超塑成型技术研究

以典型热作模具钢的复杂型腔为对象,研究了超塑制模的工模具设计及工艺,成型出连杆精锻模具型腔。系统归纳、总结了工模具钢超塑制模技术的特点并展望了未来发展趋势。     

基于INTERNET的超塑性数据库系统

介绍了首个基于国际互联网INTERNET的超塑性数据库，包括超塑性简介、超塑性材料、超塑性文献、超塑性专家、单位等，为广大的超塑成形工作者提供服务。     

变形条件对MB15镁合金组织性能及其超塑性的影响

采用自行设计的热模拟试样,研究变形条件对MB15镁合金力学性能及组织影响的规律,并对热压缩后的MB15镁合金试样超塑性性能进行了试验研究。研究结果表明,对于MB15镁合金,当变形温度为300℃、应变速率为5.0×10-3s-1、变形程度为80%时,MB15镁合金具有良好的综合力学性能;当变形温度为340℃、应变速率为5.56×10-3s-1时,延伸率可达到307.9%;当应变速率在5.56×10-4s-1~1.0×10-2s-1范围时,延伸率≥251.2%。     

电沉积纳米复合材料的超塑性研究

采用脉冲电沉积技术制备了含不同Al2O3颗粒的Al2O3/Ni-Co纳米复合材料,在应变速率从8.33×10-4s-1到1.67×10-2s-1,温度从723K到823K的范围内,研究了它们的超塑性拉伸变形行为,确定了最佳超塑性条件并获得了最大延伸率.采用SEM和TEM对电沉积和超塑变形前后试件的显微结构进行了表征.应用晶粒长大行为和协调机制对合金和复合材料的超塑性进行了对比研究和讨论.     

生物医用Ti-29Nb-13Ta-5Zr合金的超塑性行为

采用拉伸速率突变法,研究Ti-29Nb-13Ta-5Zr(Ti-29-13)合金冷轧后在700~800 ℃和5′10-4~1′10-2 s-1应变速率范围内的高温变形行为和变形机制,并与典型β钛合金Ti-15V-3Cr-3Sn-3Al(Ti-15-3)进行比较。结果显示两种合金中均出现了非连续屈服现象,Ti-29-13合金的亚晶行为不同于Ti-15-3合金。Ti-29-13合金的延伸率低于Ti-15-3合金,应力指数n几乎恒定为3.3,变形激活能为152~161 kJ/mol;Ti-15-3合金在730 ℃以上的n值为2.3~2.5,变形激活能为173~176 kJ/mol。     

双相NiAl金属间化合物超塑性

研究双相Ni-31Al金属间化合物的高温变形行为。结果表明,该合金在950~1075℃温度范围,1.25×10-4~8×10-3s-1应变速率范围内呈超塑性变形。在温度为1000℃、应变速率为5×10-4s-1时,最大延伸率可达281.3%。显微结构分析表明,超塑性变形过程中两相具有很好的协调变形能力,超塑性变形后原始组织拉长、细化。双相Ni-31Al金属间化合物超塑性变形机制可能为连续动态回复与再结晶。     

Superplastic behavior of friction-stir welded Al–Mg–Sc–Zr alloy in ultrafine-grained condition

The present work was undertaken to improve superplastic ductility of friction-stir welded joints of ultrafine-grained (UFG) Al–Mg–Sc–Zr alloy. In order to suppress the undesirable abnormal grain growth, which typically occurs in the heavily deformed base material, the UFG material was produced at elevated temperature. It was suggested that the new processing route could reduce dislocation density in the UFG structure and thus enhance its thermal stability. It was found, however, that the new approach resulted in a relatively high fraction of low-angle boundaries which, in turn, retarded grain-boundary sliding during subsequent superplastic tests. Therefore, despite the successful inhibition of the abnormal grain growth in the base-material zone, the superplastic deformation was still preferentially concentrated in the fully-recrystallized stir zone of the material. As a result, the maximal elongation-to-failure did not exceed 700%.     

镁合金超塑性的变形机理﹑研究现状及发展趋势

综述不同成形条件下的镁合金激活能及本构方程,对粗晶和细晶镁合金的超塑性变形机理予以详细的介绍。并对常见的几种镁合金超塑性加工方式进行探讨,并概述超塑性镁合金的发展趋势,认为未来超塑性镁合金将取得快速发展。获得高应变速率与低温超塑性镁合金并实现镁合金低成本化、安全化、环保化是目前研究的热点。     

Microstructure evolution and mechanical behavior of AZ31 Mg alloy processed by equal-channel angular pressing

AZ31 Mg alloy bar was subjected to 8-pass equal-channel angular pressing(ECAP) at 623 K. Microstructure evolution was observed by optical microscopy(OM) on cross section and X-ray diffraction analysis. The room temperature mechanical properties of the ECAP processed specimens were also investigated. A fine-grained structure with an average sub-grain size of 9 μm is obtained after 7 ECAP passes. XRD analysis indicates that after ECAP, in placing of planes and become the dominant directions that are favourable for grain refinement. ECAP processed AZ31 Mg alloy exhibits significant improvement in elongation but decrease in strength. The elongation of the specimen increases continuously up to 2 passes and then remains stable at further passes. This improvement can be related to the evolution of crystallographic texture and the scattered orientation of the basal plane (0001).