Zhang Milin

Influence of Rare Earth Elements on Microstructure and Mechanical Properties of Mg-Li Alloys

Abstract A series of α-based Mg-Li-Al-Zn- x RE alloys were prepared. These alloys have low density ranging from 1.5 to 1.7 g· cm −3 and high strength properties. The influence of RE element on the microstructure and the mechanical properties of these alloys were studied. The results indicate that the addition of RE (La, Pr, Ce) leads to the formation of rodshaped intermetallic compound Al 2 Zn 2 La distributed in the matrix. Al 2 Zn 2 La induces reduction of the laminar spacing and causes refinement of the microstructure. Therefore, this compound improves the strength of alloys at a high temperature.

Electrochemical Behavior of Dy(III) and the Selective Formation of Dy-Ni Intermetallic Compounds in LiCl-KCl Eutectic Melts

采用循环伏安、方波伏安和开路计时电位等电化学方法研究了Dy（III）离子在Li Cl-KCl共晶盐中的电化学行为及Dy-Ni合金形成的电化学机理.循环伏安和方波伏安法研究表明,Dy（III）离子的电化学还原过程为三个电子转移的一步反应.与惰性W电极相比,Dy（III）离子在Ni电极上的循环伏安曲线多出了三对氧化还原峰,是由于Dy与Ni形成了合金化合物,导致Dy（III）离子在活性Ni电极发生了欠电位沉积.采用X射线衍射（XRD）和扫描电子显微镜（SEM）附带能量散射谱（EDS）对恒电位（-1.6,-1.8和-2.0 V）电解制备的Dy-Ni合金进行分析,分别获得了DyNi5,Dy2Ni7和DyNi2金属间化合物.实验结果表明,通过控制电位进行恒电位电解可以有选择性地制备不同的金属间化合物.

Wide-band underwater acoustic absorption based on locally resonant unit and interpenetrating network structure

The interpenetrating network structure provides an interesting avenue to novel materials. Locally resonant phononic crystal (LRPC) exhibits excellent sound attenuation performance based on the periodical arrangement of sound wave scatters. Combining the LRPC concept and interpenetrating network glassy structure, this paper has developed a new material which can achieve a wide band underwater strong acoustic absorption. Underwater absorption coefficients of different samples were measured by the pulse tube. Measurement results show that the new material possesses excellent underwater acoustic effects in a wide frequency range. Moreover, in order to investigate impacts of locally resonant units, some defects are introduced into the sample. The experimental result and the theoretical calculation both show that locally resonant units being connected to a network structure play an important role in achieving a wide band strong acoustic absorption.

EFFECTS OF COMBINED ADDITION OF Y AND Nd ON MICROSTRUCTURE AND TEXTURE AFTER COMPRESSION OF Mg-Li ALLOY AT ROOM TEMPERATURE

Due to the super light-weight property,Mg-Li alloys are very promising in the fields of aerospace and military defense.Up to now,many studies about hot deformation behavior of Mg-Li alloys have been reported.However,there are little researches on their room-temperature deformation behavior.Therefore,the plastic deformation mechanism of Mg-Li alloys needs further investigated.It is known that addition of RE to Mg alloys could cause solid solution strengthening, fine grain strengthening and secondary phase strengthening.Nevertheless,reports refer to the effect of RE on the texture of Mg-Li alloys.This work was devoted to study the microstructure,mechanical properties and the evolution of texture after compression at room-temperature of the as-cast Mg-5Li-3Al-2Zn and Mg-5Li-3Al-2Zn-1.2Y-0.8Nd alloys with OM,SEM,XRD,ODF and EBSD techniques as well as material testing machine.The results show that with the addition of Y and Nd,most of the filamentous AlLi intermetallic compounds are suppressed and substituted by other two intermetallics Al_2Y and Al_(11)Nd_3.Meanwhile,the grains are refined with the average size of 30μm.ODF analysis indicates that for Mg-5Li-3Al-2Zn alloy,when the strain is 0.17 the C-axis of most grains is roughly 75°form ND,while in Mg-5Li-3Al-2Zn-1.2Y-0.8Nd,when the strain is 0.10 the strong prismatic texture appeares,which means that the(1010) of most grains parallel to ND. Both of the two alloys exhibit high plasticity when tested at room-temperature,while the compression deformation of the alloy containing Y and Nd can reach up to 27%.The combined addition of Y and Nd significantly reduces the c/a of the magnesium lattice,weakes basal texture,activates the pyramidal slip system and,especially,activates the prismatic slip system which seldom occurs at room-temperature in magnesium alloys.

A Wide Band Strong Acoustic Absorption in a Locally Network Anechoic Coating

Composite materials with interpenetrating network structures usually exhibit unexpected merit due to the cooperative interaction. Locally resonant phononic crystals (LRPC) exhibit excellent sound attenuation performance based on a periodical arrangement of sound wave scatters. Inspired by the interpenetrating network structure and the LRPC concept, we develop a locally network anechoic coating (LNAC) that can achieve a wide band of underwater strong acoustic absorption. The experimental results show that the LNAC possesses an excellent underwater acoustic absorbing capacity in a wide frequency range. Moreover, in order to investigate the impact of the interpenetrating network structure, we fabricate a faultage structure sample and the network is disconnected by hard polyurethane (PU). The experimental comparison between the LNAC and the faultage structure sample shows that the interpenetrating network structure of the LNAC plays an important role in achieving a wide band strong acoustic absorption.

Performance Improved by Incorporating of Ru Atoms into Zr-Si Diffusion Barrier for Cu Metallization

Thin Ru21Zr64Si15 films deposited on Si substrates by radio frequency reactive magnetron sputtering are studied and evaluated as diffusion barriers for Cu metallization. Cu/Ru21Zr64Si15/Si and Cu/Zr67Si33/Si structure samples are prepared under the same procedures for comparison. The thermal stability, phase formation, surface morphology and atomic depth profile of the Cu/Ru21Zr64Si15/Si and Cu/Zr67Si33/Si structures before and after annealing at different temperatures are investigated. In conjunction with these analyses, the Cu/Ru21Zr64Si15/Si contact system shows high thermal stability at least up to 650°C. The results obtained reveal that the incorporation of Ru atoms into the Zr67Si33 barrier layer is shown to be beneficial for improving the thermal stability of the Cu/barrier/Si contact system.

Direct Electrochemical Formation of Different Phases Al-Y Alloys by Codeposition in LiCl-KCl Melts

Abstract Electrochemical preparation of different phases Al-Y alloys were investigated in LiCl-KCl-AlCl 3 -Y 2 O 3 melts at 773 K by cyclic voltammetry, square wave voltammetry, open circuit chronopotentiometry and polarization curve. The electrochemical measurements show that the underpotential deposition (UPD) of Y on pre-deposited Al forms two Al-Y intermetallic compounds. The results of X-ray diffraction (XRD) indicate that the two different Al-Y intermetallic compounds are Al 2 Y and α -Al 3 Y. The microstructure and the micro-zone chemical composition of Al-Y alloys were characterized by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS), respectively. The results illustrate that element Y is mainly distributed on nubby precipitates. Different phases Al-Y alloys can be obtained by adjusting the concentration of AlCl 3 .

New preparation of Mg-Li-Al alloys by electrolysis in molten salt

This work presents a study on electrochemical formation of Mg-Li-Al alloys on an inert electrode(Mo electrode) in a molten KCl-LiCl-AlCl3-MgCl2-KF system.It aims at preparation Mg-Li-Al metal alloy directly under an optimal electrolytic parameters.Main factors which affect current efficiency are investigated.We have discussed the co-electrodeposition conditions and the effect of technical parameters on these experiments,and gained a good electrolytic process.The result of calculation shows that co-electrodeposition Mg,Li and Al occurs at the cathode current density higher than 9 A/cm2 and electrolytic voltage between 6 to 9 V.And at the optimal parameters,12-13 A/cm2,620-640 ℃,the highest current effciency reaches as high as 86%.Lithium combined with magnesium forms Li0.92Mg4.08 and Li3Mg7,and aluminum mainly exists in a form of Mg0.58Al0.42,distributing in the alpha phases and beta phases.

Underpotential Deposition of Al-Ce Alloys at an Al Electrode from LiCl-KCl-CeCl3 Melts

Abstract Electrochemical behavior of Ce(III) and underpotential deposition of Al-Ce alloys were investigated at an Al active electrode in LiCl-KCl-CeCl3 melts. Compared with the cyclic voltammetry curves on a Mo electrode, the redox potential of Ce(III)/Ce at the Al electrode is more positive; there are two new plateaus between the deposition plateau of Al and Ce metal by open circuit chronopotentiometry, which means two kinds of intermetallic compounds. All above show Ce(III) forms intermetallic compound by underpotential deposition electrochemically. Furthermore, it is also confirmed by Al-Ce alloys, which are obtained at the Al active electrode in LiCl-KCl-CeCl3 melts after potentiostatic deposition under the same condition. The formation of AlCe and AlCe3 is illuminated by X-ray diffraction (XRD). The reasons of AlCe and AlCe3 formation were explained by XRD and phase diagram of Al-Ce. The standard Gibbs free energies of AlCe and AlCe3 formation were calculated by XRD and open circuit chronopotentiometry. The analysis of scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) reveals that cerium exists at the surface of Al electrode to form an Al-Ce alloys layer, which is about 28 μm in thickness, and evenly coated the Al electrode.

Electrochemical Behavior and Extraction Efficiency Evaluation of Gd in Chloride Molten Salt System

The electrochemical behavior and thermodynamic properties of GdCl3 in LiCl-KCl molten salt system on both Mo and Al electrodes at 773 K were investigated. An open circuit chronopotentiogram was used to determine the equilibrium potentials and standard apparent potentials of the Gd(III)/Gd(0) system in the temperature range 723-873 K. The results showed that the equilibrium potentials and apparent standard potentials became positive with increasing temperature. The activity coefficients of GdCl3 were calculated at different temperatures. The depolarization values were calculated by steady state polarization tests, and the theoretical extraction efficiency was obtained at 773 K. Potentiostatic electrolysis was performed to extract gadolinium from LiCl-KCl-GdCl3 molten salt on Al electrodes at-1.5 V. The extraction efficiency was about 94.22% after 20 h. The Al3Gd phase was identified in the deposit by X-ray diffraction (XRD).