Study On The Micro Thixoforming Process Of Semi-Solid A356 Alloy In Meso Scale

Supported by "Research on the theory and method of ultrasonic assisted semi-solid micro thixoforming in meso-scale", a project from National Natural Science Foundation of China (Grant No.50775203), the key problems of semi-solid micro thixoforming were analyzed on the new issue of applying semi-solid forming technology into microforming field. The mechanism and processing of inductive heating for A356 alloy, the flow stress constitutive model at semi-solid temperature range of A356 alloy, finite element analysis and numerical simulation for micro thixoforming process, the experiment research and processing parameters optimization for micro thixoforming were studied.In Chapter 1, the background and significance of this research, the current research situations of metal microforming technology, the key technical problems of semi-solid metal forming and the micro thixoforming technology were introduced, then the research contents of this thesis were proposed.In Chapter 2, the effects of induction reheating parameters, such as reheating steps, reheating time, holding temperature and holding time, on the microstructure of the billet were studied. Based on the research results of induction reheating parameters, the heating schemes for billets in different shape were designed. The induction heating experiment results were analyzed under optical microscope.In Chapter 3, based on the data of uniaxial isothermal compression test on Gleeble 1500D thermal simulator, the flow stress of semi-solid A356 in high temperature range was investigated. The relationships between deformation behavior and deformation parameters were studied. At last, based on the Arrhenius equation, the flow stress constitutive model of A356 in high temperature range was obtained through multiple linear regression analysis.In Chapter 4, the forming process of semi-solid A356 aluminium alloy was simulated by applying the thermo-mechanically coupled rigid-viscoplastic FEM in Deform-3D. The effects of forming parameters, such as punch speed and friction condition, on the workpiece were investigated. Meanwhile the formation mechanism of workpiece with micro-pins was studied.In Chapter 5, an experimental study on semi-solid micro thixoforming processing parameters in meso scale was conducted, and the reaction plate for micro-channel reactor for hydrogen production from methanol steam reforming was manufactured. Firstly, the semi-solid micro thixoforming experiment setup was built, then the influences of processing parameters on the reaction plate part were studied by orthogonal experiment design. Based on the analysis of processing parameters, optimum parameters were obtained after generally balancing the forming indicators. Finally, semi-solid micro thixoforming technology was applied in the manufacture process of reaction plate for micro-channel reactor for hydrogen production from methanol steam reforming.In Chapter 6, the chief work of this thesis were summarized, and further research subjects were proposed.