Research On The Microstructure And Properties Of Rolling-Casting Of Semi-solid Magnesium Alloy

Magnesium alloy, which fulfills the requirements of lightweight and friendly to environment for materials, has very vast development foreground as a new engineering materials because of its low density, high strength-to-weight ratio, high modulus, good heat conductivity, superior damping characteristic, good machinability, and so on. Semi-solid metal processing technology, synthesized the merits of liquid-casting technology and solid-press forming technology, is catching many researchers'attention in various fields and is regarded as one of the near-net shape forming technologies with wide application in 21 century。Twin roll casting process is a kind of technology which combines fast solidification and continuous deformation progresses together. In recent ten years, there has been growing interest in the research of twin-roll rapid casting of thin-strip near end product shape in the world, which is thought to be one of the most potential technologies in the metallurgy and material field. The process has many advantages over the conventional casting technique. The primary advantages are of enhancing production efficiency, saving energy and reducing production cost, at the same time, it is potential to improve quality of casting strip.Today the consuming of Magnesium in the world wide are becoming more and more, China is a rich resource country of Magnesium。But our production levels is backward and its manufacturing cost are very high, which reduced the market ratio and limited the development of Magnesium。So it is crucial to expoit the new low cost and short stage technology applied to produce Magnesium and enlarge its using。The technology of Semi-solid strip by Rolling-Casting is a whole new technology which is high efficience,energy conservation,short stage and near end product shape, which is the combination of the semi-solid technology and the roll casting technology。Magnesium Alloy manufactured by this technology is a technological innovation which can widen the application of the semi-solid and cast-roll technology, can develop the manufacture of Magnesium to provide next procedure with the strip, fulfills the requirements of lightweight and friendly to environment for materials, develop our resouces especially in western zone。This paper researched the process of the semi-solid AZ91D by casting-rolling。Firstly the semi-solid slurry was gotten by the semi-solid manufacturing equipment which is the nondendritic grain; secondly, the slurry was casted and rolled on the casting-rolling equipment and got the semi-solid casting-rolling strip; then the microstructure and the properties was tested。Furthermore, the simulation experiment was carried out in computer by the finite element method. On the numerical and experimental base, the technical parameter was optimized by the orthogonal design and neural network.The result is1. The experiment of AZ91D semi-solid castin-rolling was carried out on the equipment made by ourselves, AZ91D semi-solid castin-rolling strip was gotten, whose microstructure is the the first crystallization non-dendrite particle distribute in the matrix.2. it was found that there is an obvious effect on the semi-solid microstructure by casting and rolling in the experiment. Before and after casting and rolling the microstructure is different, before is somewhat dendritic, after is near ball which is the globurization by casting and rolling。The solid ratio is different with the casting-rolling temperature, low temperature high solid ratio。3. The numerical model was studied by deal with heat conduction and convection in the flow of the slurry using the conversion of the convection coefficient, deal with the latent heat because of the crystallization using enthalpy. The simulation showed that the temperature gradient higer nearer the entrance of casting-rolling, the temperature gradient lower nearer the exit of casting-rolling. It was also studied the effect of the temperature of casting-rolling, the speed of casting-rolling, the gap of roller, the temperature of roller and the diameter of roller on the temperature field of casting-rolling.4. On the numerical and experimental base, the technical parameter was optimized by the orthogonal design and neural network. The optimum slurry manufacture parameters is stirring speed: 1000r/min, static time: 5 min, stirring time: 5 min, casting temperature 560℃。The optimum casting-rolling parameters is casting-rolling temperature 723K, casting-rolling speed: 0.5m/s, roll gap: 2mm, roll coiling: small water cool, roll diameter: 210mm。5. on the base of the experiment the process of slurry manufacturing and casting-rolling is two dependent and independent process, which can freely combined together。6. The further hot-cold working showed: AZ91D semi-solid castin-rolling strip has a big plasticity。The cold total deformation is 28%, the hot total deformation47%。...