The stoichiometric alloy MlB5.0 and the hypo-stoichiometric alloy MlB4.85 were prepared by twin-roller rapid quenching process, and their structure and electrochemical properties were studied. The results of XRD show ...The stoichiometric alloy MlB5.0 and the hypo-stoichiometric alloy MlB4.85 were prepared by twin-roller rapid quenching process, and their structure and electrochemical properties were studied. The results of XRD show that both of the alloys have a typical single-phase hexagonal CaCus-type structure. The cell volume of the hylpo-stoichiometric alloy M1B4.85 is slightly larger than that of the stoichiometric alloy M1B5.0, although its lattice constant cla is smaller. Under 2 C discharging rate, i.e. 640 mA/g, the M1B4.85 has a discharge capacity of 320 mAh/g, which is higher than that of the M1Bs.o, 312 mAh/g. Nevertheless, the capacities of the M1B4.85 and the M1Bs.o decline 24.7% and 20.2% after 400 cycles, respectively. The relationship of electrochemical performances of the alloys with their structures is discussed.展开更多
The effect of set-back distance on the thermo-mechanical behavior of the strip during twin roll casting(TRC)of an AZ31 magnesium alloy was modeled using finite element method(FEM).Model validation was done by comparin...The effect of set-back distance on the thermo-mechanical behavior of the strip during twin roll casting(TRC)of an AZ31 magnesium alloy was modeled using finite element method(FEM).Model validation was done by comparing the predicted and measured exit strip surface temperature as well as the secondary dendrite arm spacing(SDAS)through the thickness of the sheet to those measured during experiments.Model results showed as the set-back distance increases,the strip exit temperature decreases and the solidification front moves toward the entry of the roll gap.The cast strip also experiences more plastic deformation and consequently,the normal stress on the strip surface and effective strain at the strip center-line increase.Moreover,higher separating forces were predicted for longer set-back distances.Model predictions showed that changing the set-back distance by varying the final thickness has a more significant effect on the temperature and stress-strain fields than altering the nozzle opening height.展开更多
In order to study the mechanism of grain refinement induced by laser shock processing （LSP） in AZ31 magnesium alloy, the specimens were processed with Nd：glass pulse laser shocking and the microstructures of LSP sp...In order to study the mechanism of grain refinement induced by laser shock processing （LSP） in AZ31 magnesium alloy, the specimens were processed with Nd：glass pulse laser shocking and the microstructures of LSP specimens near the surface were examined by optical microscopy and transmission electron microscopy. Optical microstructure pictures show that the size of grains formed in the top surface layer is about 4-6 μm, which is obviously different from the original grains （with an average size of 20-30 μm） in the substrate in AZ31 magnesium alloy. Transmission electron microscopic observations show that the grain refinement process of AZ31 alloy by laser shock processing includes three stages. At the early stage of LSP, the lower strain and strain rate activates the three dislocation slip systems which include basal plane system, prismatic plane system and pyramidal plane system, with the deformation governed mainly by dislocation. At the intermediary stage, dislocation slip is hindered at grain boundaries and becomes more difficult to continue during LSP. Then, parallel twins appear, which divide the original coarse grains into finer twin platelets. Finally, high-density dislocation walls are formed and subdivide twins into sub-grains. Dynamic recrystallization occurs in the process of further deformation and forms recrystallized grains when strain energy reaches the value needed by recrystallization, which leads to refinement of the grains in the top surface layer.展开更多
基金[This project was supported by the National Natural Science Foundation of China (No. 20373016), the Key Project of In-ternational Science and Technology Cooperation of MOST of China (No. 2005DFA60580), the Key Project of Guangdong Province (No. 2005B50101003), and the Excellent Young Teachers Program of MOE of China.]
文摘The stoichiometric alloy MlB5.0 and the hypo-stoichiometric alloy MlB4.85 were prepared by twin-roller rapid quenching process, and their structure and electrochemical properties were studied. The results of XRD show that both of the alloys have a typical single-phase hexagonal CaCus-type structure. The cell volume of the hylpo-stoichiometric alloy M1B4.85 is slightly larger than that of the stoichiometric alloy M1B5.0, although its lattice constant cla is smaller. Under 2 C discharging rate, i.e. 640 mA/g, the M1B4.85 has a discharge capacity of 320 mAh/g, which is higher than that of the M1Bs.o, 312 mAh/g. Nevertheless, the capacities of the M1B4.85 and the M1Bs.o decline 24.7% and 20.2% after 400 cycles, respectively. The relationship of electrochemical performances of the alloys with their structures is discussed.
基金The authors of this work would like to appreciate the NSERC(Natural Sciences and Engineering Research Council of Canada)Magnesium Strategic Research Network(MagNET)for the financial support of this work and the Natural Resources Canada Government Materials Laboratory,CanmetMATERIALS located in Hamilton,Ontario for providing the opportunity to perform the experimental parts of the work.The assistance of Dr.M.Kozdras,Dr.A.Javaid,Dr.E.Essadiqi and Mr.G.Birsan and P.Newcombe(from CanmetMATERIALS)in processing the experimental data is gratefully acknowledged.
文摘The effect of set-back distance on the thermo-mechanical behavior of the strip during twin roll casting(TRC)of an AZ31 magnesium alloy was modeled using finite element method(FEM).Model validation was done by comparing the predicted and measured exit strip surface temperature as well as the secondary dendrite arm spacing(SDAS)through the thickness of the sheet to those measured during experiments.Model results showed as the set-back distance increases,the strip exit temperature decreases and the solidification front moves toward the entry of the roll gap.The cast strip also experiences more plastic deformation and consequently,the normal stress on the strip surface and effective strain at the strip center-line increase.Moreover,higher separating forces were predicted for longer set-back distances.Model predictions showed that changing the set-back distance by varying the final thickness has a more significant effect on the temperature and stress-strain fields than altering the nozzle opening height.
基金Funded by National Natural Science Foundation of China(Nos.51275221 and 51175231)the Natural Science Foundation of Jiangsu Province,China(No.BK2011261)+1 种基金Qing Lan Project,Jiangsu Province,Chinathe Applied Science Foundation of Changzhou City,Jiangsu Province,China(No.CJ20159051)
文摘In order to study the mechanism of grain refinement induced by laser shock processing （LSP） in AZ31 magnesium alloy, the specimens were processed with Nd：glass pulse laser shocking and the microstructures of LSP specimens near the surface were examined by optical microscopy and transmission electron microscopy. Optical microstructure pictures show that the size of grains formed in the top surface layer is about 4-6 μm, which is obviously different from the original grains （with an average size of 20-30 μm） in the substrate in AZ31 magnesium alloy. Transmission electron microscopic observations show that the grain refinement process of AZ31 alloy by laser shock processing includes three stages. At the early stage of LSP, the lower strain and strain rate activates the three dislocation slip systems which include basal plane system, prismatic plane system and pyramidal plane system, with the deformation governed mainly by dislocation. At the intermediary stage, dislocation slip is hindered at grain boundaries and becomes more difficult to continue during LSP. Then, parallel twins appear, which divide the original coarse grains into finer twin platelets. Finally, high-density dislocation walls are formed and subdivide twins into sub-grains. Dynamic recrystallization occurs in the process of further deformation and forms recrystallized grains when strain energy reaches the value needed by recrystallization, which leads to refinement of the grains in the top surface layer.
