Research On High Vacuum Die-casting Process For Aluminum Alloys

During the process of die-casting, air is unavoidably entrapped into the liquid metal because of the process's high speed and high pressure, and this will cause gas porosity occurred in the die castings. Because of the air holes, common die castings don't adapt to be heat-treated to improve their mechanical properties. The high vacuum die-casting is an effectual method to decrease air holes and improve the mechanical properties of die castings. MFT(Minimum Fill Time) method is a high vacuum die-casting process more suitable for small-scale die-casting plants. Based on the MFT method, researches were done in the aim of developing a vacuum shut-off valve and its vacuum system for high vacuum die-casting. Experiments were also done to prove that the vacuum shut-off valve and its vacuum system can work in order, and ZL101 castings manufactured with high vacuum die-casting process adapt to be heat-treated to improve their mechanical properties.The vacuum shut-off valve for high vacuum die-casting was designed by consulting designs existed, and shares the same structure that has an initiative piston and a driven piston. Its theory is that the driven piston was forced to move through the transmission when the liquid metal hit the initiative piston. The difference happens in the transmission, a lever was used in our new design while designs existed use an integration or gears. And the lever transmits force more flexible and reliable. Also the vacuum system was computed to validate: it meets the need of high vacuum die-casting consuming less than 1s.A method of die sealing, which is based on modifying the vacuum die-casting moulds, was developed before experiments. Two kinds of ZL101 alloy castings were manufactured under the conditions of common die-casting process and high vacuum die-casting process. After comparing their appearances, mechanical properties and microstructures, it's found that the high vacuum die-casting process enhances the ZL101 alloy castings with their tensile strength to 204.55MPa and their elongation to 8.41%, better than the common die-castings by 17.16% and by 71.98%. After being heat-treated, no bubbling can be found on the surface of ZL101 castings manufactured with high vacuum die-casting process and their tensile strength was enhanced by 7.68% while their elongation was weakened by 6.78%.