Effects of Casting Pressure on Deformation of Gas Porosity in Aluminum Die Casting

This study was conducted on the mechanism of the deformation of porosity, which reduces markedly the quality of high-pressure die casting, and on the effects of injection pressure on porosity. Casting was carried out at a wide range of injection pressures between 1 MPa and 90 MPa and at different injection rates. Porosity, density and gas contents of the casts were observed and measured. In the castings produced at the very low pressure of 1 MPa and at high injection rates, the runner region had no pores and high density, while the product region had numerous pores and so its density was very low. The pores were mainly caused by gas entrapment at the gate and in the cavity. Increasing the injection pressure had no effect on the amount of gas in the product region, but increased the density with the decrease in the number of pores. This is why high injection pressure decreases gas porosity. Detailed evaluation of the change in pore volume showed that the product of injection pressure and gas volume (PVG) was constant and therefore the Boyle-Charles' law was established at injection pressures higher than 20 MPa.