Reduction of shrinkage porosities in aluminum alloy castings by external pressure fluctuation under gravity field

Abstract

S hrinkage porosity is one of the typical and most common defects in castings, which can deteriorate the properties of produced castings. It is very difficult to reduce the defects through subsequent thermomechanical treatments [1] or forging process [2] , especially for defects formed in the near-net shape casting process. A lot of research has been done to extend the service life of castings by reducing the shrinkage porosity in the castings [3-8]. Generally, this kind of defects are caused by insuffi cient feeding pressure or obstruction of the feeding channel [9-12]. The studies of many investigators show that vibration can improve the casting quality since Chernov first successfully refined grains of steel castings by gentle vibration of the mould. The application of vibration to the mould is one of the most convenient methods to improve casting quality [13]. However, there still are some drawbacks, and one example is that vibration with low frequency during the solidifi cation process usually makes