Effect Of Pressure Parameters On Properties Of A357 Alloys In Semi-Solid During Thixoforging

Semi-Solid metal processing is applied commercially in western developed countries as a new metal processing technology. But in our country, this technology is still in the stage of laboratory research or small scale production test. In this paper, the thixoforming properties and flow rule of semi-solid A357 alloy, which is one of commonly used cast alloy, has been systematically studied through single compression test and thixoforming test. The constitutive equation of thixoforming property has been established. And a finite element calculation has been applied to simulate the thixoforming process. The influence of different processing parameters on the compressive flow stress of semi-solid A357 alloy has been investigated through the isothermal compression test. It is found that the flow stress is not only the function of strain and temperature, but also the function of strain rate. The deformation mechanism of semi-solid metal has been discussed. The deformation of semi-solid metal has following modes: (1) the viscous fluid flow of liquid metal around the solid particles; (2) the slip behavior and rotary motion between solid particles; (3) breading of solid particle clusters under the pressure. The scales of above three modes will change when the semi-solid metal is deformed at different temperature and strain rate.A rigid-viscoplastic finite element calculation in DEFORMTM-3D software was performed to simulate the above thixoforming test. The metal flow velocity field, the equivalent strain field, the equivalent stress field, the rate of solidification and the law of change in relative densities were obtained.Some thixoforming experiments with different values of processing parameters on A357 alloy were carried out on the self-made die in order to study the influence of processing parameters on the deformation properties. The rule of pressure parameters influence on the real density, microstructure and mechanical properties of semi-solid A357 alloy has been investigated through discussion the real density of finish product in different pressure and height of the ingot. The simulation results were compared with the experimental data and showed good agreements.