Papers by Author: Ling Yun Wang

Abstract: The superplastic bulging test of AZ31B magnesium alloy sheet of 0.6mm thick was carried out on Alliance RT/50 tensile machine at 573K and 3.3×10^-4S^-1. It is found that either in tensile-compressive deformation or in bi-axis tensile deformation, the judgment criterion for local necking of superplastic deformation is dε₂=0. The superplastic forming limit diagram(FLD) at 573K and 3.3×10^-4S^-1 was established for the first time.

Abstract: After superplastic tensile tests and quantitative analysis of cavity volume fraction, the damage evolution equation based on the law of the micro-damage evolution and statistical mechanics was derived out. The characteristic parameters of damage evolvement and critical value of damage variables are achieved from the experiments.

Abstract: The superplastic bulging test of AZ31B magnesium alloy sheet of 0.6mm thick was carried out on Alliance RT/50 tensile machine at 573K and 3.3×10 −4 −1 s . It is found that either in tensile-compressive deformation or in bi-axis tensile deformation, the judgment criterion for local necking of superplastic deformation is 0 2 dε = . The superplastic forming limit diagram
FLDat 573K and 3.3×10 −4 −1 s was established for the first time.

Abstract: Microstructural evolution and mechanical properties of the AZ31 magnesium alloy during rolling and annealing process were investigated. The sheet samples were prepared after different stages of the hot rolling, cold rolling and annealing processes. The hot rolling temperature was between 300-450
C and the final thickness of the cold rolled sheets was 1.5mm. The cold rolled sheets were annealed at different annealing temperature (260-350
C) for different time (10~120min). Tensile test was performed to investigate the mechanical properties of the samples obtained from different stages. With aid of the optical microscopy, scanning electron microscopy (SEM) techniques, the microstructure of the samples were characterized and the results were related to the mechanical properties. It was found the hot-rolled sheets exhibit higher ductility comparing with the cold-rolled sheets. The microstructural investigation showed that the microstructure of the hot-rolled samples was dominated by recrystallized equiaxed grains while the microstructure of the cold-rolled samples dominated by deformation twining. By applying annealing on the cold-rolled sheets, fine recrystallization grains were obtained and ductility of the samples was improved. The effects of the grain size and twining on mechanical properties of the AZ31 sheet were further discussed based on the experimental results.

Abstract: The dynamic recrystallization characteristic of 3104 alloy has been investigated by isothermal compression deformation at temperatures from 573K to 773K under constant strain rates ranges from 10-3s-1 to 1s-1. It was shown that the form of flow stress curves were very sensitive to temperature and strain rate. At high temperatures and low strain rates, dynamic recrystallization of 3104 alloy deformation occured. The critical value for dynamic recrystallization start was determined from an inflection point that was observed in the plot of work hardening rate vs. flow stress and verified metallograhically based on quenching samples interrupted during deformation. In the experimental domain studied, the ratio of the critical strain for the initiation of dynamic recrystallization to that of the peak strain falled in the range 0.4-0.6. Furthermore, the dependence of εc on Zener-Hollomon parameter( Z) has been developed.

Abstract: In this paper, the basic formability of stamping of magnesium-alloy AZ31B sheet has been studied through experiments. The stamping formability of magnesium-alloy AZ31B sheet, such as the conical cup value, bending formability, deep drawing formability, formability of hole expanding, forming limit has been studied by simulating processing experiments. The formability of stamping supplies the basic reference data for the stamping processing. It is also found that the formability of stamping of magnesium-alloy AZ31B sheets is poor at room temperature and is excellent at intermediate and high temperatures.

Abstract: A model was developed for the analysis and prediction of correlation between composition and mechanical properties of Mg-Al-Zn (AZ) magnesium alloys by applying artificial neural network (ANN). The input parameters of the neural network (NN) are alloy composition. The outputs of the NN model are important mechanical properties, including ultimate tensile strength, tensile yield strength and elongation. The model is based on multilayer feedforward neural network. The NN was trained with comprehensive data set collected from domestic and foreign literature. A very good performance of the neural network was achieved. The model can be used for the simulation and prediction of mechanical properties of AZ system magnesium alloys as functions of composition.

Abstract: Conventional manufacturing processes of metal and alloys sheets are rolling. The poor formability of magnesium alloys at room temperature makes rolling difficult. In the present paper, a manufacturing technique of sheets by powder rolling was employed to fabricate magnesium alloy sheets. The technique consisted of roll compaction, sintering, re-rolling and annealing. Powders of Mg-3 wt% Al mixed using a global mill were roll compacted into green sheets using two counter rotating rolls to the thickness of approximately 0.60 mm. Roll compacted green sheets were sintered at 823 K in argon atmosphere. Sintered green sheets were then re-rolled at ambient temperature to approximately 0.22 mm to obtain fully dense sheets. There was no significant edge cracking observed in the process of cold rolling. It is reasonable to believe that powder rolling is a promising technique for manufacturing magnesium alloys sheets.

Abstract: Recent research and development status of wrought magnesium alloys in China is reviewed, and more attentions are paid to structure controlling, plastic processing, welding, surface treatment and product application. The control of alloy phases, grain refinement, deforming behavior and twin-roll strip casting process are discussed. The existing problems on the research and development of wrought magnesium alloys in China are analyzed.

Abstract: The deformation behavior of AZ31 magnesium alloy has been investigated by isothermal compression at temperatures between 573-723K and at constant strain rates ranging from 10-3 -1s-1. It is shown that the form of flow stress curves is very sensitive to temperature and strain rate. In the experimental domain studied, the flow stresses are modeled using a power law with an average activation energy of 145.16 kJ/mol, and dynamic recrystallization (DRX) occurs. The critical strain for DRX is determined by analysis of flow stress curves. The ratio of the critical strain to the peak strain falls in the range of 0.4-0.5. At low temperatures and high strai rates, the deformation become macroscopically inhomogeneous, and the fracture of the specimens is accompanied by shear banding. Grain refinement resulting from DRX is less effective at high temperatures due to rapid grain growth. It is also shown that there is no difference between peak stress and stable state stress at high temperatures and lower strain rates, presenting the feature of continuous dynamic recrystallization (CDRX).