The electrochemical behaviors of Mg-5Li-3Al-1La and Mg-8Li-3Al-1La alloys in sodium chloride solution

The electrochemical behaviors of Mg-5Li-3Al-1La and Mg-8Li-3Al-1La electrodes in NaCl solution are investigated by means of potentiodynamic polarization, potentiostatic oxidation, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and X-ray diffraction (XRD). It is found that the Mg-8Li-3Al-1La electrode is of higher discharge activity than the Mg-5Li-3Al-1La electrode in 0.7 mol L^?1 NaCl solution, which is consistent with the results observed from SEM images. The composition of the discharging products is also analyzed by means of XRD diffraction. This result shows that the Mg-8Li-3Al-1La alloy displays better compatibility with salt than the Mg-5Li-3Al-1La alloy, and the electrolyte can easily permeate the electrode, which enlarges the reaction zone and improves the activity of the electrode. The continuous discharging utilization efficiency of the Mg-5Li-3Al-1La and Mg-8Li-3Al-1La electrodes is 47.36 and 50.46%, respectively. The utilization of the Mg-Li-Al-La electrode is increased by 3.10% with the amount of Li increased from 5 to 8%. Meanwhile, the interval discharging utilization efficiency of the two electrodes is 46.13 and 49.88%, respectively, and the increase in the amount of Li in the electrode also brings a favorable effect on the interval electrochemical properties of the electrode.     

Scaling behavior of the Portevin-Le Chatelier effect in an Al-2.5%Mg alloy

The scaling behavior of the Portevin-Le Chatelier (PLC) effect was studied by deforming an Al-2.5%Mg alloy for a wide range of strain rates. To reveal the exact scaling nature, the time series data of true stress versus time, obtained during deformation, were analyzed by two complementary methods: the finite variance scaling method and the diffusion entropy analysis. From these analyses we could establish that, in the entire span of strain rates, the PLC effect showed the Levy-walk property.     

Enhancement of ductility,weakening of anisotropy behavior and local recrystallization in cold-rolled Ti-6Al-4V alloy strips by high-density electropulsing treatment

The effect of high-density electropulsing treatment (EPT) on the microstructure, mechanical properties and fracture behavior of cold-rolled Ti-6Al-4V alloy strip was investigated. The results indicated that EPT accelerated the local recrystallization process tremendously in pre-deformed titanium alloy. The EPT-induced microstructural change resulted in remarkably increasing elongation to failure while remained tensile strength unchanged. In addition, anisotropy behavior of mechanical property is weakened dramatically. A mechanism for rapid local recrystallization in low temperature during EPT was proposed based on the reduction of nucleation thermodynamic barrier and enhancement of atomic diffusion. Uneven fractures of different direction specimens with quasi-cleavage fracture mode were gradually evolved into uniform ductile fracture mode with transgranular dimples under EPT.     

Effect of structure transformations on the microhardness of Al-15at.% Zn alloy

The ageing of single crystals of Al-15 at. % Zn alloy was studied at the temperature of 205 °C by X-ray diffraction and by measurement of microhardness. A close correlation of individual structure stages with microhardness was found on ageing the alloy.In conclusion the authors would like to express their thanks to Doc. Dr. V. Syneek CSc. for helpful discussion, to Ing. J. Laek CSc. for the careful chemical analyses of the investigated alloy and to Mr. Z. iký and Mr. S. Pazour for assistance in measurements.     

Study of ultrasonic melt treatment on the quality of horizontal continuously cast Al-1%Si alloy

The fluctuation of the melt temperature in a tundish was measured during casting and experiments were conducted to investigate the effects of ultrasonic melt treatment on the surface quality and solidification structures of Al-1%Si ingots. The results show that the uniformity of melt temperature was enhanced with the application of ultrasonic melt treatment. When the ultrasonic power is 1,000W, the surface quality was evidently improved and grains of cast ingots were refined. Moreover, EPMA analysis was adopted to study the relationship between the ultrasonic power and boundary segregation of Si element. The result shows that boundary segregation is suppressed with the increase of ultrasonic power and the phenomenon was theoretically interpreted.     

Effect of hardening temperature on the disintegration kinetics of the Al-10 at. % Zn alloy

The existence of the Al-10 at. % Zn alloy at temperatures above the equilibrium curve below about 350°C in the K state is investigated here by the methods of diffusion x-ray scattering, small-angle scattering, transmission electron microscopy, and microhardness measurements.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 3–8, April, 1986.In conclusion, the author wishes to express his gratitude to Professor H. Loeffler and to the assistants and instructors at the N. K. Krupskaya Teachers' College in Halle (GDR) for their aid in carrying out these studies with various methods, as well as for their active participation in the discussion of the results obtained.     

The influence of quenching rate on the kinetics of transformations of metastable phases in the Al-30 wt.% Zn alloy

The effect of quenching rate on the precipitation process in the Al-30 wt. % Zn alloy has been studied by the X-ray diffraction and electron microscopy. No effect has been observed both on the T-T-T curve for the transformation of coherent into semicoherent phase and on the isothermal growth of precipitates of these phases. The significant dependence has been, however, found when the ageing of the investigated alloy led to the formation of incoherent phases. The T-T-T curves for _R and _R transformations are shifted to the shorter ageing times with the increased quenching rate. The slopes of these T-T-T curves yielding parallel straight lines remain unchanged. The role of coherency stresses and of quenched-in strains in the investigated processes is discussed.In conclusion the authors would like to express their appreciation to Doc. Dr. V.Syneek, CSc. for his valuable discussions and to Ing. V.íma for the preparation of Al-Zn alloys. Our thanks are also due to Mr. V.Petr and Mr. Z.iký for their help in the heat-treatment and X-ray diffraction measurements of the investigated samples, and to Mr. P.Vyhlídka for the homogeneity control of the Al-Zn alloys.     

On the decomposition of the transition rhombohedral phase in the Al-30 wt.% Zn alloy

The decomposition of the transition rhombohedral α′_R-phase at the temperatures between 85 and 250 °C was investigated by transmission electron microscopy and by X-ray diffraction on single crystals. Below 161 °C the direct decomposition of α′_R-phase into the equilibrium hexagonal β-phase without the formation of the transition cubic α′-phase was found. Both transformation sequences α′_R → β and α/′_R→α′ → β were observed in the temperature range from 161 to 180 °C whereas only the previously known sequence α′_R → α′ → β was detected on ageing the alloy between 180 and 250 °C. The precipitation process at the temperatures from 161 to 180 °C is characterized by the decomposition of α′_R-phase into the equilibrium β-phase prior to the formation of the transition α′-phase and by the increased rate of decomposition of α′-precipitate. The observed transformation processes are related to the variation of strains at the partially coherent interface between α′_R-phase and α-matrix with the temperature in correlation with the metastable α′_R-phase boundary. These considerations allowed to estimate the relative stabilities of precipitated phases and their activation energies of formation and thus to discuss the decomposition mechanism of α′_R-phase at various temperatures.     

The effect of thermal aging on the strength and the thermoelectric power of the Ti-6Al-4V alloy

When the Ti-6Al-4V alloy is overaged at 500-600°C, nanometer-sized α₂ (Ti₃Al) particles can be homogeneously precipitated inside a phases, thereby leading to strength improvement. Widmanstätten and equiaxed microstructures containing fine α₂ (Ti₃Al) particles were obtained by overaging the Ti-6Al-4V alloy. Precipitation of α₂ (Ti₃Al) particles was monitored using thermoelectric power measurements for different aging conditions in the Ti-6Al-4V alloy. Overaging heat treatments were conducted at 515, 545 and 575°C for different aging times. In addition, overaging samples were examined by optical microscopy, scanning electron microscopy and hardness measurements. It was found that the thermoelectric power is very sensitive to the aging process in the two studied Ti-6Al-4V structures.     

The effect of phase transformations on the recrystallization texture of cold-rolled steel

The texture changes in cold-rolled steels with various degrees of reduction before and after heating them below and above the critical points Ac₁ and Ac₃, have been investigated by a magnetometric method. It is shown that at annealing temperatures above the Ac₃ point the sharpness of the recrystallization texture in general diminishes. The recrystallization texture of the first kind with negative amplitudes A₄ of the normal component of the magnetization vector (of the type {110} 001 with corresponding scattering) scarcely emerges as the dominant texture at such preliminary reductions as are obtained by cold rolling. This is due to the high-temperature heating of the iron in the -phase.     

The effect of different concentrations of Na2SnO3 on the electrochemical behaviors of the Mg-8Li electrode

In this research, the effect of the different concentrations of NaSnO₃ as the electrolyte additive in 0.7 mol L^?1 NaCl solution on the electrochemical performances of the magnesium-8lithium (Mg-8Li) electrode are investigated by methods of potentiodynamic polarization, potentiostatic current-time, electrochemical impedance technique, and scanning electron microscopy (SEM). The corrosion resistance of the Mg-8Li electrode is improved when Na₂SnO₃ is added into the electrolyte solution. The potentiostatic current-time curves show that the electrochemical behaviors of the Mg-8Li electrode in the electrolyte solution containing 0.20 mmol L^?1 Na₂SnO₃ is the best. The electrochemical impedance spectroscopy results indicate that the polarization resistance of the Mg-8Li electrode decreases in the following order with the concentrations of Na₂SnO₃: 0.05 mmol L^?1?>?0.00 mmol L^?1?>?0.30 mmol L^?1?>?0.10 mmol L^?1?>?0.20 mmol L^?1. The scanning electron microscopy studies indicate that the electrolyte additive prevents the formation of the dense oxide film on the alloy surface and facilitates the peeling off of the oxidation products.     

The effect of pulse to pulse variation on ultrashort pulsewidth measurements

An alternate interpretation is presented for the exponential shapes of the second harmonic autocorrelation functions obtained from synchronously pumped mode locked dye laser systems. The shape is reinterpreted as being due to a weighted average of pulses of varying widths and smoothly varying pulse shapes in time. Such pulse width measurements in the past have averaged over a large number of pulses. Several pulse shapes and pulse width distributions are examined all leading to exponential shaped autocorrelation functions. This interpretation implies that the currently determined pulsewidths are shorter, possibly many times shorter than the actual average pulsewidths. A method for selectively descriminating the shortest pulses from the train to increase the time resolution of current laser systems is presented.     

固溶处理对Al-Cu合金中Portevin-Le Chatelier效应空域行为的影响

研究了在定加载速率拉伸条件下，固溶处理对Al-Cu合金材料中PLC(Portevin-Le Chatelier)效应空域行为的影响.在较低拉伸速率时，变形初期PLC变形带在试件宽度方向中央附近某点处“成核”.随着变形的继续，出现多带共存的现象.且带宽较小，带与拉伸轴向的夹角较大.在较大拉伸速率条件下，PLC变形带先连续传播，再随机出现. 关键词： PLC效应 动态应变时效 固溶处理     

The effect of laser surface treatment of Al-Si alloy on the surface hardness and structure

In this paper, some samples of Al-Si alloy with various silicon content were treated by laser beam. The effects on structure, hardness and substructure of samples were investigated. The experimental results show that the primary crystal Al and eutectic silicon in the laser treated samples is got thinning obviously, the mosaic dimension is decreased and the dislocation density is increased.     

Unstable plastic flow in the Al-3% Mg alloy in the process of continuous nanoindentation

Methods of dynamic nanoindentation were used to study unstable modes of plastic flow in micro-and submicrovolumes of the Al-3% Mg alloy. It was established that, depending on the rate of loading and dimensions of the deformed region, various regimes of unstable plastic deformation are realized. In the course of deformation, the irregular deformation curve (corresponding to a random process) reveals a quasi-periodic behavior with a characteristic amplitude of hardness oscillations.     

The effect of the shear flow on directional solidification of SCN-3wt% Salol alloy

The directional solidification process of SCN-3wt% Salol transparent alloy is investigated in the presence of the shear flow at the liquid-solid interface. It is found that the shear flow induces a stabilizing effect on planar interface. At higher pulling rates, oscillation of the growth pattern together with fluctuation of the growth velocity takes place. With the increase of the pulling rate, the interface growth pattern transits from “planar-cellular” oscillation to “cellular-dendritic” oscillation, and the periodicity increases. The modification of the growth pattern is due to the effect of the shear flow on solute distribution, and the time and history dependent character of interface morphology evolution also plays an important role in the formation of the oscillating growth pattern. Supported by the National Natural Science Foundation of China (Grant Nos. 50331040 and 50702046)