Investigation On Creep Age Forming Of2A97Aluminum Alloy

Abstract:In this paper, the age forming process and creep aging behavior of2A97aluminum alloy has been investigated systematically. The effect of process parameters on the tensile strength and springback has been studied in the age forming and and gained the optimal parameters. The effects of age forming and stress free ageing on microstructures and mechanical and corrosion properties of the alloy were studied comparatively. The creep strain curve of the alloy was measured. The mechanism of creep aging has been explored and established the creep aging constitutive model of the alloy. The results are as follows:(1) The relationship between the two parameters (the springback and tensile strength) and the three factors (the pre-deformation radius, aging temperature and aging time) has been studied through orthogonal design in age forming process. The range analysis shows that the order of the importance for the factors to the springback, in sequence, is the aging temperature, the aging time, and the pre-deformation radius. And the order to the tensile strength, in sequence, is the aging temperature, the pre-deformation radius and the aging time. The variance analysis indicates that the specimen have the maximal amount of springback at age forming performed at120℃for5h using a single-curvature die with a radius of1000mm and the specimen have the maximal tensile strength at age forming performed at180℃for15h using a single-curvature die with a radius of1000mm. The regression and RBFANN methods can both be used to obtain the model, however, the simulation results of the RBFANN models are in better agreement with the experimental results under any conditions. It indicates that the prediction capacity of the RBFANN model is better than that of the regression model.(2) In contrast to the stress free ageing, the dislocation caused by age forming can provide many favorable nucleation sites for T1precipitation and make it distribute more dispersively and homegenously in the grain, result in decreasing nucleation of T1precipitates in grain boundary or sub-grain boundary, delaying the formation of PFZ and reducing the time to attain peak age, the tensile properties, hardness and corrosion resistance of the alloy is also improved. (3) The average apparent stress index and average apparent activation energy of2A97aluminum alloy has been calculated as3.0274and70.991kJ/mol based on the curves of creep strain vs. time of the alloy. According to the typical creep mechanism, that the creep processes of the alloy are controlled by the dislocation glide mechanism. The classical creep constitutive model, unified ageing-creep constitutive model,θ projection concept and artificial neural network model has been established for2A97aluminum alloy. All of the four model can have a better description of the creep aging behavior of the alloy.