Papers by Author: Ding Fei Zhang

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Authors: Xu Yang, Fu Sheng Pan, Ding Fei Zhang
Abstract: With the aim of evaluating corrosion inhibition for various inhibitors, a new qualitative method for corrosion inhibition effect test for magnesium and magnesium alloys was developed. The change of polarization current density of AZ61 magnesium alloy in electrochemical polarization experiments in alkali aqueous solution with 5mmol/L sodium dodecylsulphate(SDS), phytic acid(PA), ethylenediamine tetraacetic acid(EDTA), p-nitro-benzene-azo-resorcinol(PNBAR), acidum tannicum(AT) or stearic acid(SA) were tested. The SEM-EDS techniques and deposition experiment method were used for further confirmation of the corrosion inhibition. The results showed that those organic compounds which could form the inhibitor-magnesium precipitation in aqueous solution could be used as corrosion inhibitors for magnesium alloys to inhibit the increase of polarization current density as well as the dissolution and oxidation of magnesium alloys effectively.
Authors: Hong Jun Hu, Ding Fei Zhang, Fu Sheng Pan
Abstract: In order to study the influence of die structures and process parameters on ECAE for wrought magnesium alloy AZ31 and obtain optimized process parameters, the three-dimension(3D) new geometric models with different corner angles (90o,120o,135o) and with or without inner round fillets in the bottom die were designed. The simulation results showed that the loads of top dies declined mainly with the corner angles increasing and inner round fillets of the bottom dies manufactured, the bottom die with inner round corner and the corner angle of 90o was propitious to improve the plasticity and deformation homogeneity of the billets.
Authors: Ding Fei Zhang, Li Bo Cui, Yu Ping Liu
Abstract: The effect of different factors on the corrosion performance of the anodic film formed on AZ31 was studied by using electrochemical impedance spectroscopy (EIS) and Tafel polarization curves techniques. The result of EIS showed that the oxide film formed at 20 mA·cm-2 had the highest corrosion resistance and the optimum temperature was 40°C. The similar conclusion was drawn by the Tafel polarization curves. Moreover, the equivalent electrical circuit R(C(R (QR))) (CR) was used to analyze the EIS data.
Authors: Jian Peng, Ding Fei Zhang, Pei Dao Ding, Fu Sheng Pan, Xiang Yu
Abstract: In this paper, the flow stress curves during thermal deformation of AZ61B magnesium alloy have been measured by isothermal compression tests on Gleeble-1500D thermal simulation instrument, and effects of deformation temperature and strain rate on flow stress were analyzed. The thermal deformation activation energy of AZ61B alloy could be work out at 185.64 KJ/mol by means of empiric dynamic equation of elevated temperature deformation. The softening mechanism of AZ61B alloy under the testing condition of thermal deformation has been identified to be dynamic recrystallization.
Authors: Bin Chen, Ji Luo, Quan Yuan, Ding Fei Zhang, Guo Zheng Quan
Abstract: The mechanical response and failure of the specimens of magnesium alloy AZ61 with different heating rates (HR) and loading rates (LR) were investigated by a Gleeble-1500 thermal-mechanical material testing system. It was found that heating rate has markedly effect on the strength and plasticity of the specimens. The higher the heating rate is, the lower the strength and the smaller of the plasticity of the specimens will be. There is the relatively small effect of the loading rates on the strength and plasticity of the specimens. The metallographs of the failed specimens were also observed. It shows that there are many microvoids in the specimens near the fracture sections. These microvoids may come from the local thermal and stress inconsistency under high heating rate and loading rates and degrade the strength and plasticity of the specimens.
Authors: Chun Mei Yang, Ding Fei Zhang, Pei Dao Ding, Jian Peng, Xu Hong Chen
Abstract: In this paper, the influence of the cooling rate on the solidified structure of ZK60 Mg alloy has been studied by means of Gleeble-1500D thermal simulation instrument. The result showed that the grain size and grain shape depended on the cooling rate, Primary Dendrite Arm Space ( λI ) and Secondary Dendrite Arm Space ( λII) sharply decreased with the increasing of solidifying cooling rate (v) in the range of experimental cooling rate (0.2~100K/s). When superheat was constant, the empirical formulas of the relation between λI λII and v was obtained. In addition, the dependence between micro-hardness (HV) and Secondary Dendrite Arm Space ( λII) for ZK60 casting alloy was proved to be similar with Hall-Petch formula. The empirical formula for λII-HV has been proposed.
Authors: Hong Jun Hu, Zhao Sun, Ding Fei Zhang
Abstract: Based on characteristics of direct extrusion for magnesium alloy seamless tube and continuous equal channel angular pressing (ECAP) of tubes, a new composite extrusion process of tubes including direct extrusion and many steps ECAP was invented firstly, which are shorten for TES process in this paper. A three-dimensional finite element thermo-mechanical coupled model and conditions for TES process were established. The extrusion process and cumulative strains evolution during TES process were simulated. The results show that TES process can improve the cumulative strains significantly. The microstructures observations of longitudinal sections for tubes fabricated by direct extrusion and TES process were carried out. It was found that when the extrusion temperature was 400°C, and extrusion ratio was 8.4 and the channel angle was 150°, TES process can refine the microstructures of tubes effectively.
Authors: Ding Fei Zhang, Li Ping Ren, Hong Ju Zhang, Wei Yuang
Abstract: Developing new alloys and techniques is important for the applications of magnesium alloy products. The greatest challenge in the area is to exploit new wrought magnesium alloys[1]. In this paper, the effects of Zn addition on the microstructures and mechanical properties of the MZK60 wrought alloy which is modified from ZK60 have been investigated. The microstructures of these alloys at various states were evaluated by optical microscopy. The mechanical properties at room temperature of these alloys were studied systematically by tensile test. Experimental results indicated that increasing Zn content to 7~10%wt is able to get not only higher tensile strength and yield strength, but also higher elongation.
Authors: Ding Fei Zhang, Yu Ping Liu, Chang Guo Chen, Ya Juan Xu
Abstract: In this work, the galvanic corrosion behavior of AZ31 magnesium alloy in contact with A6N01S-T5 aluminum alloy in NaCl solution was investigated by electrochemical method, the salt immersion method, SEM. And three protection techniques: (a) rubber gasket technique ,(b)organic coating technique and (c) anodizing technique were used to inhibit the galvanic corrosion. The results of open circuit potential and polarization curve method were explained the corrosion behavior of AZ31 and A6N01S-T5.It was found that AZ31 as anode was accelerated corrosion and A6N01S-T5 as cathode was also corrode in salt immersion experiment. With the increasing of immersion time, the corrosion rate of AZ31 and A6N01S-T5 was gradually decreasing. Then, the efficacy of different anti-corrosive technologies was compared. Fluorine coating technique was an effective way to protect Mg alloy and Al alloy. It was possible to guide the anti-corrosion of magnesium alloy in mobile industry.
Authors: Bin Chen, Quan Yuan, Ji Luo, Ding Fei Zhang, Guo Zheng Quan
Abstract: The effects of strain rate (SR) and heating rate (HR) on the mechanical behaviors of the tensile specimens of magnesium alloy AZ61 were experimentally investigated using a Gleeble-1500 thermal-mechanical material testing system. It showed that the higher the temperature is, the lower the ultimate strength of the specimens will be. The higher the heating rate is, the higher the ultimate strength of the specimens will be. The metallurgraphs of the fracture section of the specimens were also experimentally investigated for exploring their failure mechanism under different temperatures and heating rates. It showed that the high temperatures and high heating rates will induce microvoids in the specimens. The microvoids make the specimens failure under relative low loads.
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