Effect of process parameters on porosity distributions in high-pressure die-cast AM50 Mg-alloy

High-pressure die-casting is the preferred manufacturing process for cast Mg-alloy components used for numerous applications. High-pressure die-cast components usually contain micro-porosity that adversely affects their mechanical properties. In this contribution, the effects of three important process parameters, gate velocity, intensification pressure, and melt temperature on the micro-porosity distributions in high-pressure die-cast AM50 Mg-alloy are quantitatively characterized. The amounts of total porosity, gas porosity, shrinkage porosity, and pore size distributions are experimentally measured using novel digital image analysis techniques that permit quantification of both gas and shrinkage pores in an unbiased manner. The experimental data lead to the following conclusions: (1) Application of intensification pressure significantly reduces the total amount of porosity primarily via reduction in the gas porosity. The intensification pressure significantly reduces the number density and area fraction of the gas pores larger than 100 mu m diameter. (2) A decrease in the gate velocity decreases the total amount of porosity predominantly via a decrease in the gas porosity and a small extent of decrease in the shrinkage porosity. The lower gate velocity uniformly decreases the number density and area fraction of gas pores of all sizes (small and large). (3) A decrease in the melt temperature also reduces the total amount of porosity primarily via reduction in the gas porosity. The lower melt temperature reduces the number density and area fraction of the gas pores larger than 30 mu m. (c) 2006 Elsevier B.V. All rights reserved.