| Cast Aluminum-Silicon alloys are used in automotive and industrial weight sensitive applications because of their low density and excellent castability. The presence of trapped gas and or shrinkage pores in certain locations within castings has been shown to influence mechanical properties such as tensile strength and fatigue life. These micromechanical defects can be found most anywhere in a casting depending on processing conditions. A large amount of porosity located in the center of the casting may have no effect on mechanical properties or fatigue performance. A smaller, isolated pore near a surface may have a significant impact on mechanical properties. Hence, it is important to develop a comprehensive model to predict the size, location and distribution of microporosity in castings.; In this work, we model the effect of various casting process parameters on microporosity formation for equiaxed aluminum A356 alloy castings. The process parameters include cooling rate, hydrogen content of the melt, grain refiner and eutectic modifier melt additions. The two dimensional model predicts the size, morphology and distribution of microporosity at a given location in the casting. The method couples a mathematical model of porosity evolution with a probabilistic grain structure prediction method. The porosity evolution model is based on the simultaneous solution of the continuity and momentum equations for the metal and the mass conservation equation for the dissolved gas. It incorporates various solidification phenomena such as the formation of a dendritic phase, hydrogen evolution at the solid/liquid interface, solidification shrinkage, interdendritic fluid flow, and formation and growth of pores. Microshrinkage porosity, which has not been modeled by mathematical models, can also be predicted by the proposed approach. Two permanent mold gravity casting experiments were conducted to verify the proposed model. The comparisons between experimental results and simulations demonstrate good agreement. |
