Uniform texture in Al-Zn-Mg alloys using a coupled force field of electron wind and external load

Cylindrical Al-Zn-Mg alloys were processed by electroplastic compression with forced air cooling.Compared to a simple compression process,an unequal intensity of {110} <111> was obtained,and other textures were eliminated by electroplastic compression,that is,electroplastic compression can promote a uniform texture.The various textures formed in different regions along the radial direction under a simple compression process were illuminated by analyzing the relationship between the crystal rotation and stress state.Furthermore,the interaction between the electrons and dislocations was studied in electroplastic compression.The electrons enhanced {110} <111> by promoting slipping of the dislocations when the Burgers vectors of the dislocations were parallel to the drift direction of the electrons.However,the electrons also inhibited crystal rotation by pinning the dislocations with the Burgers vectors perpendicular to the drift direction of the electrons.Therefore,textures other than {110} <111>have difficulty forming under electroplastic compression.The effect of the current energy on the texture(enhancement or attenuation) was in accordance with the law of conservation.The results provided reasonable explanations for the test phenomena.     

On the additivity of acoustoplastic and electroplastic effects

The influence of high density current pulses (approximately 10³ A mm⁻² for 25–80 μs) and the ultrasonic deformation (2 × 10⁴ Hz) on the flow stress of Cu tested in uniaxial tension at 300 K were investigated with the objective of determining the mechanisms of the joint action of electroplastic (EPE) and acoustoplastic (APE) effects. The experimental procedure used allows synchronization of the current pulse and the ultrasonic deformation and allows the current pulse and the ultrasonic deformation to be shifted in phase. It was found that the combined APE + EPE is smaller than the sum of separate effects and depends on the phase shift between the current pulse and the ultrasonic deformation. An extremum of the combined APE + EPE at a certain phase shift between the current pulse and the ultrasonic deformation was detected. An increase in the EPE after prior action of ultrasonic deformation was detected. Employing the thermally activated plastic flow concept, a differential equation for combined APE + EPE is proposed.     

Influence of electric current on superplastic deformation mechanism of 5083 aluminium alloy

5083 aluminium alloy superplastic forming adopted resistance heating can not only improve efficiency and cut energy but also generate electroplastic/electrosuperplastic effect to make the material deformation possess lower flow stress and higher plasticity. By analysing the influence of current on dislocation slipping, grain boundary migration and dynamic recrystallisation, it is found that the electron wind force can enhance the mobility of dislocations; meanwhile, the current also can reduce the activation heat of dislocation motion by joule heating effect. What is more, the grain size of resistance heating forming sample is significantly smaller than furnace heating, and the cavities in the sample become small and dispersive, so the resistance heating forming specimen possesses better performance.     

Electroplasticity Mechanisms in hcp Materials

Herein, the mechanisms of the electroplastic effect (EPE) in different hexagonal close-packed (hcp) metals under varying loading conditions and current densities through the analysis of flow curves and microstructural changes are investigated. The investigations show a significant change in the forming behavior of the hcp materials as a result of superimposed electric current impulses. This behavior could be attributed to two effects. On the one hand, additional dislocation types are activated; on the other hand, new characteristic twin bands are formed. This is shown for all three hcp materials under investigation: Ti, Mg, and Zn. Furthermore, the hypothesis of the existence of a critical value of the current density at which a significant change in the plastic behavior occurs is verified by the experiments. The magnitude of this critical value for the analyzed hcp materials corresponds approximately to the theoretical values reported to be in the range of 1.6 to 2.0 kA mm⁻². In addition to the current density, the duration of the pulses also has an influence on the EPE. Understanding the correlation between the individual activated deformation mechanisms during electric pulse treatment can be crucial for controlling the electroplastic forming processes in a systematic and targeted manner.     

The influence of electroplastic rolling on the mechanical deformation and phase evolution of Bi-2223/Ag tapes

Electroplastic rolling (EPR) of Bi-2223/Ag superconducting wires was performed, where pulse currents were applied during rolling to introduce an electroplastic effect. It was found that the rolling force decreased significantly compared with the traditional rolling process. Furthermore, EPR favorably minimized the sausage effect. It is revealed that the electroplastic effect can facilitate the mechanical deformation of Bi-2223/Ag composites. Segments of the Bi-2223/Ag tapes were heat treated at 830 °C for different time periods. The phase assemblies of these samples suggest that current pulses contribute to faster transformation kinetics from the Bi-2212 phase to the Bi-2223 phase. In addition, a preliminary improvement of 28% of critical current density has been achieved in a fully processed tape with EPR.     

AlN颗粒在不同铝合金中的增强行为

LD2为了解AlN颗粒对不同强度等级的铝合金的增强效果及机制 ,对 40 %体积分数的AlN颗粒增强 10 70、10 6 1、LY12铝合金复合材料拉伸前后的微观组织进行了观察 ,发现拉伸前在基体中存在由热错配引起的高密度位错 ,在AlN颗粒的内部也存在大量的位错 ,拉伸后基体中的位错增殖 ,同时 ,AlN颗粒中的位错亦增多 .力学性能的测试结果表明 ,AlN颗粒对低强度、高塑性的L3纯铝增强率最高 ,中等强度、较高塑性的LD2铝合金不仅有较高的增强率 ,而且保持了一定的塑性 .AlN颗粒对基体的这种选择性主要与AlN颗粒在拉伸过程中产生微量变形 ,从而松弛部分界面应力有关 .LY12基体的塑性较低 ,易产生低应力断裂 ,因此 ,AlN颗粒的增强作用难以得到充分发挥 .     

Dynamic Piezoresistivity Calibration for Eddy Current Nondestructive Residual Stress Measurements

It has been recently demonstrated [M. P. Blodgett and P. B. Nagy, J. Nondestruct. Eval. 23, 107 (2004)] that eddy current conductivity measurements can be exploited for near-surface residual stress assessment in surface-treated nickel-base superalloy components. To quantitatively assess the prevailing residual stress from eddy current conductivity measurements, the piezoresistivity coefficients of the material must be first determined using known external applied stresses. These calibration measurements are usually conducted on a reference specimen of the same material using cyclic uniaxial loads between 0.1 and 10Hz, which is fast enough to produce adiabatic conditions. Therefore, the question arises whether dynamic calibration measurements can be used or not for accurately assessing the sensitivity of the eddy current method for static residual stress. It is demonstrated in this paper that such dynamic calibration measurements should be corrected for the thermoelastic effect, which is always positive, i.e., it increases the conductivity in tension, when the material cools down, and reduces it in compression, when the material heats up. For low-conductivity titanium and nickel-base engine alloys the thermoelastic corrections are relatively modest at ≈5–10%, but for high-conductivity aluminum alloys the difference between the adiabatic and isothermal properties could be as high as 50%.     

7075铝合金的力学与电化学交互作用

用慢应变速率拉伸(SSRT)技术研究了7075铝合金在应力腐蚀过程中的力学与电化学交互作用.结果表明,外加极化会提高7075铝合金的应力腐蚀敏感性,这种通过极化而改变铝合金表面电化学反应从而影响断裂应力的现象是一种电化学-力学效应.然而,对于不同热处理状态的7075铝合金,外加极化对敏感性的影响程度不同.增加拉伸应力,7075-RRA铝合金的阳极极化曲线略向正移,滞后环面积扩大,但并不显著.这种拉伸应力对极化曲线的影响是一种力学-电化学效应,有利于应力腐蚀裂纹的扩展.铝合金在应力腐蚀过程中的电化学作用和力学作用是交互的,彼此促进的.     

Mg–3Al–1Zn alloy strips processed by electroplastic differential speed rolling

The effect of reduction per pass on the mechanical properties, microstructure and texture evolution of Mg–3Al–1Zn magnesium alloy strips processed by electroplastic differential speed rolling has been investigated. With increasing reduction per pass, the mechanical properties of the rolled strips increase. Both the shear effect and the current pulses play an important part in modifying the microstructure and texture by promoting dynamic recrystallisation. During dynamic recrystallisation, nucleus tends to nucleate in the vicinity of the shear bands. And as the progress of dynamic recrystallisation, shear bands are gradually consumed by the newly nucleated grains and become nearly indistinguishable. The athermal effect of current pulses plays an important role in promoting dynamic recrystallisation.     

Effects of strain and electropulse duration on elastic modulus of TiNi alloy

The elastic modulus of TiNi alloy was tailored by electroplastic rolling deformation and the effects of rolling strain and electropulse duration on the elastic modulus of electroplastic rolled TiNi alloy were systematically investigated. With rolling strain increasing from 0 to 1.70, the elastic modulus decreases from 61 to 30?GPa, which can be attributed to the increase in dislocation density and deformation-induced low modulus B19^′ martensite phase. With electropulse duration increasing from 80 to 120?µs, the elastic modulus first decreases due to the volume fraction increase in low modulus B19^′ martensite phase and then slightly increases on account of the dynamic recovery of dislocation and reverse martensite transformation resulted from electroplastic effect induced by high-energy electropulse.     

Experimental investigation of pulse current on mechanical behaviour of AZ31 alloy

The effect of pulse current on the mechanical properties of AZ31 alloy is investigated through uniaxial tensile test at different temperatures. The electroplastic effect is evaluated by the change of ultimate strength. During tensile test, both microstructure evolution and fracture behaviour are sensitive to the applied deformation conditions. In this work, the influence of pulse current is discussed from the point of view of microstructure evolution and fracture characteristics. The experimental results show that the dynamic recrystallisation temperature of AZ31 is reduced by the pulse current and continuous dynamic recrystallisation is found at 100°C for tensile test with current. The data also indicate that the pulse current accelerates the precipitation and dissolved of the second phase particles in AZ31 alloy.     

AIN颗粒在不同铝合金中的增强行为

LD2为了解A1N颗粒对不同强度等级的铝合金的增强效果及机制，对40％体积分数的A1N颗粒增强1070，1061，LY12铝合金复合材料拉伸前后的微观组织者了观察，发现拉伸前在基体中存在的热错配引起的高密度位错，在A1N颗粒的内部也存在大量的位错，拉伸后基体中的位错增残，同时，A1N颗粒中的位错亦增多，力学性能的测试结果表明，A1N颗粒对低强度，高塑性的L3纯铝增强率最高，中等强度，较高塑性的LD2铝合金不仅有较高的增强度，而且保持了一定的塑性，A1N颗粒对基休的这种选择性主要与A1N颗粒在拉伸过程中产生微量变形，从而松驰部分界面应力有关，LY12基体的塑性较低，易产生低应力断裂，因此，A1N颗普的增强作用难以得到充分发挥。     

Micromechanics of Tension‐Compression Asymmetry of Polycrystalline Shape‐Memory‐Alloys

The asymmetry associated with martensitic transformations observed in tension/compression experiments of shape‐memory‐alloys (SMAs) is investigated on the basis of a recently suggested micromechanical model. The approach is based on crystallographic theory and utilizes a framework of energy minimization in a finite deformation context. Polycrystalline NiTi under tension demonstrates smaller phase‐transformation start‐strain, differe phase‐transformation stress‐levels and flatter phase‐transformation stress‐strain slopes than that under compression in our numerical simulation. The phase‐transformation start‐stress is followed to have a linear relationship with respect to the temperature within a certain range. These results agree well with experimental results reported in the literature.     

The nature of the electroplastic effect in metals

On the basis of an analysis of the known regularities of the electroplastic effect (EPE) the article suggests a mechanism of plastic deformation of metallic materials when electric current pulses (ECP) act; in accordance with this mechanism the energy of conduction electrons is transferred directly to dislocations and is realized in the form of plastic work. The plastic strain rate at the instant when an ECP acts increases in consequence of the increased density of the moving dislocations and the mean speed at which they move. The article shows that the suggested mechanism makes it possible to describe all the known regularities of the EPE. With the aid of theoretical modeling of electroplastic deformation by the suggested mechanism new regularities of the EPE were established: when ECP act, the temperature of the deformed material is lower than that calculated by the Joule law of electric heating; the threshold value of the current density determining a jump of the load becomes lower with increasing degree of plastic deformation of the material, etc. The established regularities of the EPE were experimentally confirmed.Translated from Problemy Prochnosti, No. 1, pp. 47–51, January, 1991.     

A new algorithm for estimating fatigue life under mean value of stress

This paper discusses two problems: allowing for mean value of torsional stress and the variability of material properties with out of‐parallel fatigue characteristics. The effect of normal mean stress and shear mean stress is modified by reduction coefficients, which, to a large extent, depend on the value of existing loads. These coefficients have been developed experimentally on the basis of an analysis of the findings from fatigue tests on 2017A‐T4 and 6082‐T6 aluminium alloys and S355 alloy steel. The methods of calculation, suggested in this paper, are applicable to the materials in elastic–plastic state. The suggested algorithm for estimating fatigue life for the combination of bending or tension and compression and torsion under shear stress is based on Kluger's stress criterion. The usability of the algorithm was verified by comparing the calculation results with the results of own experimental tests on 2017A‐T4 and 6082‐T6 aluminium alloys, which have been noted to indicate sensitivity to shear mean stress, and the tests found in the professional literature (tests on S355, 30CrNiMo8 and 30NCD16 steel and Ti‐6Al‐4 V titanium alloy). A comparative analysis of the calculation and experimental results proved that there is a satisfactory correlation between them.     

Weld residual stress effects on fatigue crack growth behaviour of aluminium alloy 2024-T351

The interaction between residual stress and fatigue crack growth rate has been investigated in middle tension and compact tension specimens machined from a variable polarity plasma arc welded aluminium alloy 2024-T351 plate. The specimens were tested at three levels of applied constant stress intensity factor range. Crack closure was continuously monitored using an eddy current transducer and the residual stresses were measured with neutron diffraction. The effect of the residual stresses on the fatigue crack behaviour was modelled for both specimen geometries using two approaches: a crack closure approach where the effective stress intensity factor was computed; and a residual stress approach where the effect of the residual stresses on the stress ratio was considered. Good correlation between the experimental results and the predictions were found for the effective stress intensity factor approach at a high stress intensity factor range whereas the residual stress approach yielded good predictions at low and moderate stress intensity factor ranges. In particular, the residual stresses accelerated the fatigue crack growth rate in the middle tension specimen whereas they decelerated the growth rate in the compact tension sample, demonstrating the importance of accurately evaluating the residual stresses in welded specimens which will be used to produce damage tolerance design data.     

Fatigue crack growth in heat-treated aluminium alloys

Fatigue crack propagation tests have been performed in several heat-treated aluminium alloys under constant amplitude loading. All experiments were performed, in load control, in a servo-hydraulic closed-loop mechanical test machine. The tests were carried out using middle tension, M(T), specimens. The influence of stress ratio and thickness were analysed. Crack closure was monitored in all tests by the compliance technique using a pin microgauge. A strong stress ratio and material dependence effects on the fatigue crack growth were observed. These effects are discussed in terms of the different dominant closure mechanism. The crack growth behaviour of heat-treated aluminium alloys depends mainly on whether the dominant closure mechanism is plasticity-induced or roughness-induced. The enhancement of roughness-induced closure promotes higher crack growth resistance in these alloys. Roughness-induced closure dominates crack closure in aluminium alloys age hardened by naturally ageing and also artificially aged alloys with higher contents of Mn and Cr elements. In alloys aged hardened by artificially ageing and simultaneously with a lower content of these alloying elements plasticity-induced closure is dominant.     

基于拉弯比的焊缝名义应力的提取

为了获得任意拉弯组合载荷下焊缝的名义应力,利用纯弯和纯拉压载荷下的应力集中系数,引入拉弯组合名义应力换算系数,将基于纯拉压名义应力的焊缝疲劳性能数据,转换为疲劳损伤一致的、基于拉弯组合名义应力的焊缝疲劳性能数据．为了消除有限元建模导致的计算误差,引入单元尺寸影响因子,将拉弯组合的计算应力转换为拉弯组合的名义应力．通过上面2个转换,引入拉弯组合计算名义应力换算系数,将有限元中的拉弯组合计算应力转换为基于拉压载荷疲劳试验的名义应力,从而在具体的焊缝结构疲劳强度评估时可以直接使用拉压载荷下的疲劳试验数据．计算结果表明：拉弯组合计算名义应力换算系数与拉弯比、拉弯应力集中因子比和有限元模型中拉弯单元尺寸影响因子有关．通过选择合适的单元尺寸,使得拉压单元尺寸影响因子等于拉弯应力集中因子比,且弯曲单元尺寸影响因子等于1,可使得拉弯组合计算名义应力换算系数恒等于拉压单元尺寸影响因子,而与拉弯比无关．     

Development and properties of Ti–In binary alloys as dental biomaterials

The objective of this study is to investigate the effect of alloying element indium on the microstructure, mechanical properties, corrosion behavior and in vitro cytotoxicity of Ti–In binary alloys, with the addition of 1, 5, 10 and 15 at.% indium. The phase constitution was studied by optical microscopic observation and X-ray diffraction measurements. The mechanical properties were characterized by tension and microhardness tests. Potentiodynamic polarization measurements were employed to investigate the corrosion behavior in artificial saliva solutions with and without fluoride. In vitro cytotoxicity was conducted by using L929 and NIH 3T3 mouse fibroblast cell lines, with commercially pure Ti (CP–Ti, ASTM grade 2) as negative control. All of the binary Ti–In alloys investigated in this work were found to have higher strength and microhardness than CP–Ti. Electrochemical results showed that Ti–In alloys exhibited the same order of magnitude of passivation current densities with CP–Ti in artificial saliva solutions. With the presence of NaF, Ti–10In and Ti–15In showed transpassive behavior and lower current densities at high potentials. All experimental Ti–In alloys showed good cytocompatibility, at the same level as CP–Ti. The addition of indium to titanium was effective on increasing the strength and microhardness, without impairing its good corrosion resistance and cytocompatibility.     

Effects of the aluminum concentration on twin boundary motion in pre-strained magnesium alloys

We investigated the effects of Al concentration on the reciprocated motion of twin boundaries in pre-strained Mg-Al-Zn alloys through a combination of applied compression and tension,in-situ electron-backscattering diffraction observations,and high-angle annular dark-field scanning transmission electron microscopy observations.The twin growth was restricted by increased Al concentration,which resulted in the occurrence of smaller-sized twins.The reverse motion of twin boundaries was also restricted,resulting in the formation of higher fractions of secondary twins and 2-5° boundaries during reverse tension.The secondary twins and 2-5° boundaries mainly contributed to the increased ultimate tensile strength of the pre-strained Mg alloys.This effect is more significant in Mg alloys with larger pre-compression.Moreover,the increased amount of the Al solute atoms,rather than the precipitates,mainly contributed to the increased strengthening effect on the twin boundary motion.Our research contributes to development of high-strength Mg alloys by stabilizing twin boundaries.