| The relation of solidification parameters to the resulting microporosity has been investigated experimentally in Al-4.5% Cu alloy castings. Plate and bar castings of Al-4.5% Cu alloy were cast in a variety of configurations and mold media, in order to cover a wide range of commercial casting practice. Castings were sectioned for density measurement; porosity values were determined from the measured densities. Solidification parameters such as thermal gradient in the freezing range, G, isotherm velocity, R, instantaneous cooling rate ;The results show that porosity at a location depends on the initial hydrogen content in the liquid alloy, the resistance to fluid flow to feed shrinkage and the pressure in the pore due to the effect of the surface tension of the liquid alloy. Microporosity formation behavior is classified into four types, one in which the porosity is less than that predicted by equilibrium considerations, equilibrium behavior, gradually increasing porosity, and rapidly increasing porosity. These effects and their relation to casting practice are discussed and some recommendations of "quality criteria" for use in the computer-aided-design and analysis of casting processes are suggested. |
