An Enhanced Johnson–Cook Model for Hot Compressed A356 Aluminum Alloy

In this work, isothermal compression tests over wide ranges of deformation parameters (deformation temperatures and strain rates) are carried out for investigating the hot deformation behaviors of low-alloyed ultrahigh strength steel 30CrMnSiNi2A. For clarifying the effects of deformation parameters on microstructural evolution and dynamic recrystallization (DRX) nucleation mechanisms, the optical microscope (OM) and transmission electron microscope (TEM) are employed. It is found that DRX easily take place and the initial microstructures are greatly refined under low deformation temperatures (920 and 970 ° C ) or high strain rates (1 and 10 s -1 ). The DRX behaviors are nearly completed with the strain rate decreasing or deformation temperature increasing, and the DRXed grain growth takes place. Under high strain rates, the uncompleted DRX aggravates the inhomogeneous grain distribution, thus the average grain size initially decreases and then increases with the strain rate decreasing. It is also found that discontinuous DRX behavior characterized by grain boundary migration takes place under various deformation parameters. Besides, the dislocation cells and subgrains are detected under the strain rate of 10 s -1 , which means continuous DRX mainly takes place under high strain rate. According to the experimental data, an Arrhenius type model and a physically-based model are constructed, respectively. The good agreements between the reproduced and measured stresses indicate that both models enjoy the excellent capability in reproducing the hot deformation behaviors of 30CrMnSiNi2A steel.

Hot deformation behaviors of low-alloyed ultrahigh strength steel 30CrMnSiNi2A: Microstructure evolution and constitutive modeling

The complexity of hot deformation behaviours of metallic materials is acknowledged in decades of study. The present work uses a new constitutive model by Zhu-Ou-Popov (ZOP model) and its modifications to predict the hot deformation behaviours of metals. The ZOP model and its modifications are introduced firstly. The basic idea of these models is centred on a set of piecewise and transition functions: the piecewise functions are used to predict flow stress at different strain ranges, whilst the transition functions enable a smooth shifting from small strain to large strain ranges. The methods for identification of four variant models are developed and given in detail. Hot compressive flow stress curves of 42CrMo at different strain rates and temperatures are used to show the validity of these models. Results show that, all of the developed models are able to predict the hot compressive behaviour of 42CrMo. Using the Arrhenius type equation and modified Zener-Holloman parameter to predict the flow stress from the yield point, the Modified model Ⅲ gives the most favourable prediction accuracy with R2 of 0.9569, whilst other models are also effective with R2 higher than 0.91. The modifications of the ZOP model can be used to predict the yield stress and to reflect the peak stress. In addition, the applicability and advancement of the presented constitutive models are discussed. The models are considered to be effective in reflecting the occurrence and completion of dynamic recrystallization (DRX) in hot deformation of metallic materials. It is shown that the studied models are capable of predicting the peak strain and completion strain of DRX, with comparable results obtained to experimental data. 

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Constitutive modelling of hot deformation behaviour of metallic materials

In this paper, the hot deformation behavior of Zn–22Al alloy was investigated by performing hot compression tests under different deformation conditions. The Arrhenius-type constitutive model was developed and the constants were determined for this alloy. In addition, the processing map was constructed using the principle of the dynamic materials model (DMM). The results show that the Arrhenius-type model, with an activation energy of 63.722 kJ/mol, can provide an accurate prediction of the flow behavior of the alloy at various conditions. The higher energy dissipation efficiency was observed in the high-temperature ranges and low strain rates. The results showed that the unstable processing zone of Zn–22Al alloy has mainly occurred at high strain rates and low-temperature region. Besides, it is found that the strain has less significant effects on instability parameter and power dissipation efficiency.

An investigation of hot deformation behavior of Zn–22Al alloy and development of its processing maps during isothermal compression

Modified Johnson–Cook model of SWRH82B steel under different manufacturing and cold-drawing conditions

The compression experiments of as-received A356 alloy were conducted at temperatures ranges from 300 to 500 °C with varying strain rates. The influence of deformation parameters on the strain softening of flow stress were researched. The observation of microstructure indicated that high temperature and large strain were favorable for dynamic recrystallization behavior. In order to improve the predictability, a modified Johnson-Cook (JC) model considering strain softening mechanism was proposed. The JC model and modified JC model were calculated according to experimental data. In contrast with the JC model, the new proposed model had the better correlation and the smaller average absolute error (1.46%). Furthermore, thermal compression experiments at constant reduction speed and finite element simulations based on the new model were performed. High consistency of load-displacement curve indicated that new model had good prediction accuracy for the A356 aluminum alloy.

A modified Johnson-Cook model considering strain softening of A356 alloy

Preparation of chemically etched surface texture and its friction characteristics in sheet forming


 Tube hydroforming (THF) technology is widely applied, especially in the automotive and aircraft industries. Material characteristics of tubular workpieces should be evaluated in terms of bending and THF processes. A mathematical model, which combines the assumption of elliptical contour of a bulged wall and the prediction equation of wall thickness, is provided to analyze the THF process and to obtain the strain-stress relationship of tubes. Material characteristics of a DC04-welded tube is obtained by using a self-designed THF test machine. Considering the effects of pre-work hardening, we discuss the material strain-stress relationships of the tube and original sheet blank. An approximate determination method is proposed to obtain the stress-strain curve of the tube by using the curve of the original sheet blank and the hardness of the tube and sheet blank. A suitable constitutive equation with pre-work hardening is applied to the DC04-welded tubes through simulation and experimental methods.

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Bin Han

Papers

A modified Johnson-Cook model considering strain softening of A356 alloy

Preparation of chemically etched surface texture and its friction characteristics in sheet forming

Material Characteristics Evaluation for DC04-Welded Tube Hydroforming