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

为了防止全球变暖和节约能源，铝合金和镁合金等轻合金的使用越来越多，并且由于这些合金的可焊性较差，需要开发具有高生产率的高压压铸件。然而，传统的高压直流工艺不易生产出可靠的产品。我们为开发超高真空高压直流新工艺做了基础性工作，取得了以下成果：(1)经验证，使用所提出的浇口密封，石墨模具的模腔可减小到7kPa，金属模具的模腔可减小到3kPa。虽然这个真空度值比工厂常规获得的要好，但我们无法达到1kPa的目标。提高真空度需要对石墨模具的透气性和提高金属模具及安装的加工精度采取措施。(2)与气相高压压铸相比，真空高压压铸在型腔压力为7kPa时，其气孔缺陷大大减少，力学性能大大提高。(3)真空铸造时，表面质量也大大提高。(4)利用石墨模具和x射线对充型过程进行了直接观察，发现真空和空气环境下的充型过程非常相似，而真空条件下浇注时浇口处流入型腔的气流更加垂直。(5)充型过程与计算机模拟结果的对比表明，熔体与模具之间的润湿作用较大，考虑到这一影响的新的模拟程序已基本建立。(6)采用新型高真空高压直流电机，包括所提出的浇口密封，似乎可以生产出高质量的产品。

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.