Study On The Processing Parameters Of The Grade-controlled Solidification Of Vacuum Counter-pressure Casting Aluminum Alloy

Vacuum counter-pressure casting (VCPC) is an advanced precision forming method of the counter-pressure in which the filling and solidification processes are executed under different pressures. Because of the excellent mechanical condition during the filling and solidification processes, the VCPC is one of the most superior technology to be extensively employed to produce high quality thin wall casting, such as aerospace, defense, and automotive fields. At present, the constant pressure was employed during the solidification process of VCPC, which is unfavorable to the solidification feeding, Leading to the shrinkage porosity and the reduction of the density. Therefore, by improving the solidification keeping pressure at the right time in the middle and latter solidification stage, the grade-controlled solidification of VCPC can avoid the shrinkage porosity effectively in order to form compact microstructure.In this paper, the grade-controlled solidification of VCPC is adopted to produce aluminum alloy sample, whose density and microstructure is analyzed by means of Archimedes principle, metallographic microscope and other many analysis and testing techniques. Meanwhile, the article investigates the main process parameters, the grade-controlled time and the grade-controlled pressure, about the influence on the density and microstructure of the samples, of which there is the different wall thickness same area and the same wall thickness different area.The results indicate that the grade-controlled time has significant effect on the samples in different wall thickness, but the effect degree becomes lower with the wall thickness development. When the grade-controlled time is constant, as the development of wall thickness lots of dendrites are destroyed, resulting in the increase of grain number and dendrite refinement. With the continuous extension of the grade-controlled time, the eutectic silicon topography appears fibroid and the number of the grain is increasing firstly, reaching a maximum number and then decreasing. In compare to the single-controlled pressure, the grade-controlled pressure can observably improve the density and increase the number of grain and the refinement dendrite. The more the grade-controlled pressure increase, the better the density is, however, the increasing trend becomes smaller. Under the same grade-controlled pressure, different area has different density and the variation trend of the density is likely to be V shape from the bottom to the top.The investigation results of present paper offer the theory basis and the technical support for near net-shape technology, which can be applied to the preparation of the high-quality, large and complicated thin-wall casting production by Vacuum counter-pressure (VCPC).