Basic research on super-high-vacuum semisolid high-pressure-die casting

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The use of light alloys such as Al- and Mg alloys has been increasing to prevent global warming and save energy, and development of high-pressure-die casting (HPDC) with high productivity is required, because weldability of these alloys is bad. However, it is not easy to produce reliable products with the conventional HPDC. We have done a fundamental work to develop super-high-vacuum HPDC as a new process, and the following results have been obtained ;(1) It was confirmed to be able to reduce the cavity till 7kPa for graphite mold and 3kPa for metallic mold with using the proposed gate seal. Although this value of vacuum is better than conventionally obtained in plants, we could not achieve the target of 1kPa. Increasing the degree of vacuum requires a measure to the air permeability of the graphite mold and improving machining accuracy for metallic mold and mounting.(2) The porosity defects of sample plate castings produced by the vacuum HPDC with the pressure of the cavity of 7kPa were greatly decreased and mechanical properties greatly increased, comparing those produced by air atmosphere HPDC.(3) The surface quality was also greatly improved when cast under the vacuum.(4) Direct observation of mold filling with using graphite mold and X-ray has been succeeded, and the mold fillings under vacuum and air atmosphere were rather similar, while the flow into the cavity at gate was more perpendicular when cast under vacuum.(5) Comparison of observed mold filling with computer simulation revealed that the wetting between the melt and mold is large and a new simulation code considering the effect has been almost developed.(6) It seemed that high quality products can be produced with a new high-vacuum HPDC including the proposed gate seal.