| 2024 aluminum alloy is an aerospace alloy which has the superplasticity.With this property,superplastic bulging can obtain high quality and precision parts in a single forming process which has great potential.As the forming rate is controlled by the pressure,how to control the strain rate through the pressure and how to set the target strain rate to achieve the balance of production efficiency and quality is now the key problem.This paper will study the superplasticity of 2024 aluminum alloy and apply it to the simulation and experiments.It also studies the influence of different strain rate loading methods on the quality of bulging parts which can sustain the theory of saving time and forecasting the quality.?1?Study on superplasticity of 2024 aluminum alloy.The high temperature uniaxial tensile tests at 350?,400?,450?and 1×10-4s-1,5×10-4s-1,1×10-3s-1 strain rate were carried out to obtain the material superplastic properties under the experimental conditions.The real stress-real strain curves were fitted by several constitutive equations.The investigation shows that:the best superplasticity of the 2024 aluminum alloy is obtained at 450?and 1×10-4s-1 of which the maximum elongation is over 80%.The Backoften equation is used to fit the experimental curve which shows the strain-rate-sensitive coefficient m is larger than 0.3,so the specimen experiences the superplasticity.The strain will influence the superplasticity of the materiel and the Zener-Hollomon equation considering the compensation of strain is able to predict the superplastic deformation behavior whose error is less than 5%.?2?Study on superplastic forming simulation.The existing pressure regulation methods were summarized and a new one was put forward.Two stain rate loading methods?constant strain rate and variable strain rate?were proposed considering the influence of strain.The investigation shows that:the proposed pressure regulation method can precisely control the strain rate and the error is less than 3%.The variable strain rate loading method can significantly reduce the forming time by33%.?3?Study on superplastic forming experiments.The experimental results were obtained with the forming pressure gained in simulation.The quality of the parts was compared with the simulation results.The investigation shows that:the pressure variation law can be used to guide the experiment.The maximal thinning rate of the sheet is about 29.6%at the peak.Simulation can well predict the experiments results while the maximum error is 2.0%.Variable strain rate loading method can guarantee the quality and improve the efficiency obviously. |
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