Papers by Author: Yong Shun Yang

Abstract: In the paper, the Deform-3D software was used to simulate the mechanism of metal flow behaviour under the influence of different friction in the backward extrusion process, and further study its influence on die stress. The numerical simulation demonstrates that: smaller friction could reduce difficult deformation area of extrusion metal significantly; friction state not only affected the plastic deformation extent, but also would increase the consumption of extrusion energy; the unit pressure of punch and stress of inner wall increased along with the increase of friction, meanwhile, the ratio of them increased as well.

Abstract: The preform of Al2O3 fiber was obtained by wet method,and the result shows that the fiber distribution of preform is more uniform after the pretreatment, and the length - diameter ratio can fully meet the demand of qualified preform. The surface of preform prepared by this process is flat, and fiber is distributed evenly, with certain strength,so it can be used for pressure infiltration fabrication of alumina fiber reinforced metal matrix composites.

Abstract: The Poly-crystal alumina short fiber reinforcing 2024 matrix composites was produced by the gas pressure infiltration, and a new apparatus has been developed for the infiltration of MMCs by the gas pressure infiltration technique. The reasonable sintering parameter for the preform were determined.The preform was heated at 450°C to remove the organic binder and pore-forming material, and then heated at 1050°C for 2.5h to obtain the comprehensive properties.Scanning electron microscope was used to observe the tensile fracture of Aluminum matrix composites, and the fracture feature of composites produced in different temperature was analyzed. The melting temperature of 2024Al was 800°C and holding time was 20mins; the infiltration gas pressure was 0.5Mpa and holding time was 20s.And then interface reaction is appropriate between the fiber and matrix ,a good performance of composites was produced.

Abstract: Using the compression tests on a Gleeble-1500 thermo-mechanical simulator to study the dynamic recrystallization behaviours of AZ80 magnesium alloy in the temperature range of 593-683K and strain rate range of 0.01-10s^-1. By the analysis of the dynamic recrystallization kinetics, the Avrami exponent (m) and the constant (k) have been determined, and they aren’t constant and depend on the dimensionless parameter(Z/A).

Abstract: There are many advantages of magnesium alloy such as light mass, nonrattling and electromagnetic interference shield. Yet, its ductility was poor at room temperature and plastic forming was difficulty due to its close-packed hexagonal structure. In this paper, the superplasticity of magnesium alloy AZ91D was explored and the relationship between flow stress and true strain were achieved at different temperature by tensile tests. It was found that the flow stress of AZ91D as cast was less than 20MPa at 340-450°Cand superplastic deformation could be used to manufacture magnesium alloy parts. Utilized superplastic air bulking mold, AZ91D seamless pipes with variable cross-section were manufactured successfully based on process parameters being optimized. Moreover, the relationship between loading path of internal pressure and wall thickness was analyzed also.

Abstract: ZrO2 (3Y)-CaO-SiO2-TiO2 powders with excellent chemical homogeneity were synthesized by heating the alcohol-aqueous salt solutions. The powders have good dispersion, with particle size of 11~15nm and no hard agglomeration. The nanocomposite powders were hot-pressed in vacuum. The obtained zirconia-based multi-phase nanocomposites were characterized by using XRD and SEM, as well as relative density testing. The results demonstrated that, even though the sintering temperature was as low as 1250°C, a high relative density of 97.5% was achieved. The superplastic compressive tests of the as-sintered specimens demonstrate that this material behaves good deformability at 1350~1500°C, at which the maximum extrusion pressure is lower than 35MPa.

Abstract: By means of superplastic tensile test above the Ac1 temperature (γ→α transformation temperature), superplastic deformation activation energy of ultrafine-grained commercial die steel CrWMn is investigated on the basis of the Arrhenius theory equation, exp( / ) 1 ε& = Aσ m −Q RT , which indicates the resistance of the superplastic deformation. According to the Arrhenius equation, the activation energy is estimated from the log σt vs 1/T relationship at a constant of sensitivity index of strain rate. The results show that the strain rate sensitivity index is a constant and rather high at the conditions of superplastic deformation for the CrWMn steel, the activation energy for superplastic deformation of steel CrWMn above the critical temperature is 187KJ/mol, and the superplastic deformation activation energy is approached to the grain boundary diffusion activation energy of γ-Fe. This indicates that the grain boundary sliding (GBS) in superplastic deformation of CrWMn steel is controlled by grain boundary diffusion. The characters of superplastic deformation of the steel above the critical temperature, on the other hand, are also analyzed in this paper.

Abstract: The superplasticity of LY12 alloy was reviewed in this paper. Complex component was extruded by taking advantage of the superplasticity of supplied LY12 alloy. The research demonstrates that in isothermal compression process dynamic recrystallization may occur in supplied LY12 alloy. In superplastic forming test grain refinement was combined with initial extrusion step utilizing dynamic recrystallization to complete grain refinement, which ensured the superplasticity in supplied LY12. In the early stage of extrusion, using high deformation speed and large amount of deformation can result in grain refinement, which primarily satisfied the demand of the superplasticity. In the final stage, the forming speed decreased sharply so that the optimum strain rate was satisfied and the complicated component can be extruded successfully. The resulted product has reasonable flowing traces, which improves its service performance.

Abstract: The superplasticity of cast copper alloys used for solid cages is studied by tests of tension and compression in this paper. The results show that cast copper alloys exhibited superplasticity without any pretreatment. Cast aluminum bronze is of superplasticity at the temperatures between 750~800°C with the initial strain rate 1×10-2s-1, the elongation being over 260%. Under the condition of superplasticity compression with the strain rate (1.136~9.091)x10-4s-1 at temperatures between 600~650°C, the cast lead brass presents the superplasticity effect with the maximum flow stress under 2MPa.

Abstract: In this paper uniaxial tensile tests were carried out at temperature range of 650~810°C and initial strain rate range of 10-4~10-1s-1 to evaluate the superplasticity of as-casting aluminum-bronze QAl10-3-1.5 alloy. The superplastic forming technology (SPF) was adopted to produce solid-bearing cages made of aluminum-bronze QAl10-3-1.5 alloy. The results demonstrate that as-casting QAl10-3-1.5 copper alloy shows good superplasticity without prior-treatment. The maximum elongation of 545% is obtained at 790°C and initial strain rate of 1.0×10-2 s-1, while the maximum flow stress is only 12.4MPa. By using superplastic extrusion technology solid-bearing cages used in railway vehicles were obtained. As-extruded cages have good surface quality and the dimensional accuracy satisfies the design standards. Using this technology the production efficiency is greatly enhanced and the manufacturing cost is reduced, especially the expensive copper alloys are saved.