Fuxiao Chen

Research on the Superplastic Forming of Copper Alloy Solid-Bearing Cages Used in Railway Vehicles

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.

Study of the Superplasticity of Copper Alloys Used for Solid Cages

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.

The activation energy of superplastic flow above the critical temperature for steel CrWMn

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.