| Summary: | 碩士 === 國立中正大學 === 機械工程學系暨研究所 === 100 === Plastic processing, is also known as metal forming, it’s the effective way of production, because its process is simple, time-saving. It is suitable to product a large number of parts. In metal processing, the boundary between the billet and the dies will have high friction and high temperature , and than the boundary friction surface are exposed to high shear stress, the shear stress flow lines (Shear flow) becomes dense. In the reason, it is formation of a thin hard layer of shear flow (Thin shear boundary layer) near the boundary, and than this layer affects the uniformity of the finished product. To further explore the property, must be able to predict trends, and then develop process using different way parameters to control the region -wide changes.
Study focused on the extrusion process, the design dies of the micro-inclined angle (5 °, 10 °, 15 °), to explore if the material under different the high stress and strain will changes or not. The extruded product will be experimented by metallographic and nano-indentation, to observe the experiment from the metallographic grain distributions and changes in circumstances, in the fine grain boundary and the distribution density, then the nano-indentation hardness experiments, get a thin layer of hard layer. Equivalent thickness measuring this change, we found a different angle extrusion dies product produced the thickness of the layer is different, and calculate with the width of the layers can derive in a same material coefficient, this is the magnesium alloy material coefficient, by which material coefficients can be calculated by this process in different dies angles, to predict the next extruded magnesium alloy dies produce the thickness of layer.
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