Xuefeng Tang

Influence of process parameters on properties of AA6082 in hot forming process

Abstract The influences of process parameters on mechanical properties of AA6082 in the hot forming and cold-die quenching (HFQ) process were analysed experimentally. Transmission electron microscopy was used to observe the precipitate distribution and to thus clarify strengthening mechanism. A new model was established to describe the strengthening of AA6082 by HFQ process in this novel forming technique. The material constants in the model were determined using a genetic algorithm tool. This strengthening model for AA6082 can precisely describe the relationship between the strengths of formed workpieces and process parameters. The predicted results agree well with the experimental ones. The Pearson correlation coefficient, average absolute relative error, and root-mean-square error between the calculated and experimental hardness values are 0.99402, 2.0054%, and 2.045, respectively. The model is further developed into an FE code ABAQUS via VUMAT to predict the mechanical property variation of a hot-stamped cup in various ageing conditions.

Modeling of the flow behavior of SAE 8620H combing microstructure evolution in hot forming

With the development of net-shape forming technology, hot forming process is widely applied to manufacturing gear parts, during which, materials suffer severe plastic distortion and microstructure changes continually. In this paper, to understand and model the flow behavior and microstructure evolution, SAE 8620H, a widely used gear steel, is selected as the object and the flow behavior and microstructure evolution are observed by an isothermal hot compression tests at 1273-1373 K with a strain rate of 0.1-10 s−1. Depending on the results of the compression test, a set of internal-state-variable based unified constitutive equations is put forward to describe the flow behavior and microstructure evaluation of SAE 8620H. Moreover, the evaluation of the dislocation density and the fraction of dynamic recrystallization based on the theory of thermal activation is modeled and reincorporated into the constitutive law. The material parameters in the constitutive model are calculated based on the measured flow st...