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191.
Zn─22%Al合金的电致超塑性效应 总被引:1,自引:0,他引:1
以普通处理的Zn22%Al合金为研究对象,研究了脉冲电流对其超塑性效应的影响。结果表明,合金的延伸率显著提高并以更高的m值为特征;最佳超塑变形温度扩宽为一区间。电镜观察表明,合金局部表现出强烈的变形强化特征,同时局部又以很高的应力松驰为特点,这两个过程达到动态平衡,有效地提高了合金的均匀变形能力 相似文献
192.
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194.
Li?LinEmail author Zheng?Liu Lijia?Chen Teng?Liu Shiding?Wu 《Metals and Materials International》2004,10(6):501-506
Microstructure evolution and superplastic behaviors of ZK40 magnesium alloy were investigated in the temperature range of
473–623 K. Transmission electron microscopy (TEM) was used to study the microstructure changes. After the alloy had been processed
by equal channel angular pressing (ECAP) for one pass through the die, significant twinning was found to have occurred, and
the mean grain size was 5.6 μm. Finer grains were obtained after multi-pass ECAP, and the average grain size of the alloy
ECAPed for three passes was as low as 0.8 μm; this alloy exhibited low temperature superplasticity at 473–523 K, and the elongations
obtained at the initial strain rate of 1×10−3 s−1 were 260% at 473 K and 612% at 523 K. Corresponding values for the ZK40 alloy processed by ECAP for only one pass were 124%
at 473 K and 212% at 523 K. Poor superplastic behavior of the ZK40 alloy processed by ECAP for only one pass was related to
the longrange stresses associated with the non-equilibrium grain boundaries within the coarse grains. The incompatibility
between the fine grains and the coarse grains was thought to be unfavorable to the improvement of superplascity.
This article is based on a presentation in “The 7th Korea-China Workshop on Advanced Materials” organized by the Korea-China
Advanced Materials Cooperation Center and the China-Korea Advanced Materials Cooperation Center, held at Ramada Plaza Jeju
Hotel, Jeju Island, Korea on August 24–27, 2003. 相似文献
195.
The effect of Sc and Zr on the superplastic properties of Al-Mg-Mn alloy sheets was investigated by control experiment. The superplastic properties and the mechanism of superplastic deformation of the two alloys were studied by means of optical microscope, scanning electronic microscope and transmission electron microscope. The elongation to failure of Al-Mg-Mn-Sc-Zr alloy is larger than that of Al-Mg-Mn alloy at the same temperature and initial strain rate. The variation of strain rate sensitivity index is similar to that of elongation to failure. In addition, Al-Mg-Mn-Sc-Zr alloy exhibits higher strain rate superplastic property. The activation energies of the two alloys that are calculated by constitutive equation and linear regression method approach the energy of grain boundary diffusion. The addition of Sc and Zr decreases activation energy and improves the superplastic property of Al-Mg-Mn alloy. The addition of Sc and Zr refines the grain structure greatly. The main mechanism of superplastic deformation of the two alloys is grain boundary sliding accommodated by grain boundary diffusion. The fine grain structure and high density of grain boundary, benefit grain boundary sliding, and dynamic recrystallization brings new fine grain and high angle grain boundary which benefit grain boundary sliding too. Grain boundary diffusion, dislocation motion and dynamic recrystallization harmonize the grain boundary sliding during deformation. 相似文献
196.
Ti-6Al-4V合金超塑性变形时的组织演化 总被引:1,自引:0,他引:1
利用光学显微镜和扫描电镜对超塑性拉伸后的细晶Ti-6Al-4V合金分别进行了断口形貌分析和组织演化规律研究。结果表明:细晶Ti-6Al-4V合金室温拉伸时,断裂方式为准解理断裂;超塑性拉伸时,试样断裂的主要形式是韧窝-空洞聚集型断裂。在初始应变速率不变的条件下,随着拉伸温度的升高,α相晶粒尺寸增大,β相数量增多,空洞数量减少,且在840℃至930℃拉伸时,α相晶粒仍保持等轴状态,但在较高温度(960℃)拉伸时,α相晶粒被拉长,部分区域出现网篮组织。在拉伸温度不变时,随着初始应变速率的降低,α相晶粒尺寸增大,β相增多,空洞数量减少。高温(960℃以上)拉伸时,β相颗粒具有良好的塑性和较低的硬度,丰富的β相有利于晶界协调滑动,并对空洞的产生具有抑制作用。 相似文献
197.
198.
高速钢的组织超细化与超塑性变形力学行为 总被引:6,自引:1,他引:5
研究了W6Mo5Cr4V2高速钢的超细化热处理工艺和超塑变形力学行为。结果表明,该钢在1040℃两次循环淬火是实现其超细化的最佳热处理工艺;按此工艺进行预处理后,在810℃、初始应变速率为3.33×10^-4s^-1的最佳变形条件下,该钢的超塑伸长率可达192%,流变应力为58MPa,应变速率敏感性指数(m)为0.27。 相似文献
199.
Based on state equation that stress is the function of strain, strain-rate and temperature, the paper establishes the differential constitutive equation used for analyzing load-stability and the variational constitutive equation used for analyzing geometry-stability during superplastic tensile deformation, which contain strain hardening index, strain-rate sensitivity index, temperature sensitivity index introducted for the first time and temperature undulation index introducted for the first time in the paper. And then, based on the universal condition of plastic elementary theory, the paper analyzes load-stability and geometry-stability under continuously rising temperature and under the non-uniform temperature along the axes of specimen respectively. The results prove the impact of continuously rising speed and non-uniform value of temperature on deformation stability is that the faster temperature rises and the more non-uniform temperature is, the smaller the corresponding uniform strain of load-stability and geometry-stability are; strain hardening index is the necessary condition of stability during superplastic tensile deformation, and geometry-instability will not happen when load-instability occurs, but happen when uniform deformation has lasted after load-instability; in the superplastic temperature field, constant temperature is not necessary condition of superplasticitiy, but during the deformation, the slower temperature rises and the more uniform temperature is, the more stable deformation is. 相似文献
200.
2091铝锂合金动态再结晶诱发超塑变形中的空洞行为 总被引:8,自引:1,他引:7
研究了2091铝锂合金动态再结晶诱发超塑变形中的空洞行为.金相观察和图象分析表明,在最佳变形条件下,空洞率及空洞平均直径先随着变形增大而增大,变形至ε=1.03时,空洞率及空洞平均直径均减小,出现了超塑变形初期的空洞弥合现象.超塑变形初期的空洞形核取决于应变速率,最佳应变速率下断裂试样出现大量的圆角空洞,并且此时空洞率出现最大值. 相似文献