Constitutive Model And Numerical Simulation Of Semi-solid Forming Technology In Aluminum Alloy

In comparison to casting and forging, Semi-solid forming is such a pattern of net shape forming technologies which can offer several potential advantages, such as reduction of macro segregations, reduction of porosity and high forming efforts, which is the one of the most potential metal forming technical in the 21'th century. semi-solid forming technology can fabricate near-net-shape products using light materials, bad formability materials and shape complexity components, Based on semi-solid processing of Al-Mg-Si alloy that is popular in some industries, the structure evolution mechanism was investigated, by thermal-mechanical experiment, the semi-solid materials model and the constitutive model of semi-solid plastic deformation are proposed, and numerical simulation of the semi-solid forming is carried out using the commercial software DEFOEM-3D/ABAQUS. The results of simulation agreed well with that in experiment, so this method are feasible and effective.The reheating of semi-solid billet aims at obtaining the semi-solid structure with the spherical solid particles which is saturated uniformly in the liquid phase to ensure that semi-solid material has thixotropy. The effect of all kinds of reheating process parameters structure evolution during the reheating process, such as heating temperature, holding time, are discussed in this paper revealing the evolution of microstructure. Using the Gleeble-3000 dynamic material testing machine, Semi-solid compression tests of 6061,6063, ZL201 semi-solid billet Al alloy were carried out under different temperature and strain rate, to investigate the deformation behavior and deformation mechanism. This study considers synthetically the effects of the strain rates and the deformation temperatures on the stress-strain curves on the deformation. The results showed that the value of flow stress decreases as temperature becomes higher and as strain rate becomes lower.Semi-solid constitutive relationship reflects the material's dynamic response of the thermodynamic parameters, which is the foundation of the finite element numerical simulation. The constitutive relationship was established for semi-solid Al alloy using multiple nonlinear regression method, regression results showed that the model had high regression precision.Due to the solid phase deformation and the liquid flow in the semi-solid state, conventional metal plasticity theory and casting theory are not available for semi-solid forming. Based on the theory of fluid saturated porous media, semi-solid material is described by combining of the deformable porous skeleton for the solid phase. The finite element calculation in DEFORM-3D software has been performed to simulate the semi-solid thixo-forming process, obtaining the distribution of solid fraction and the field of stress-strain. Using simplified two-phase model in the ABAQUS software to simulate the uniaxial compression of semi-solid 6061A1 alloy, the result of the simulation are well agreed with the experiment, so the simplified two-phase model has reference to practical application. With the numerical analysis of the semi-solid, we can predict the flow behavior and deformation defects, in favor of optimizing the semi-solid process parameters.