A POROSITY MODEL FOR MULTI-GAS SYSTEMS IN MULTI-COMPONENT ALLOYS

摘要

A general framework for the modelling of porosity formation in multi-component alloys with more than one gaseous element is considered in the present contribution. It offers several advantages and accounts for: ⅰ) the partial pressure of any gaseous element composed of one or two chemical elements (e.g., H_2, N_2, CO, etc.); ⅱ) the influence of the alloy composition on partial pressures through chemical activities; ⅲ) the account of both trace gaseous elements and volatile solute elements such as zinc through appropriate mass balances. The set of equations describing multi-gas equilibrium at a given location is first described, with the construction of appropriate databases for aluminium-, copper- and iron-base alloys. These local state equations are coupled to a macroscopic resolution of the Darcy-mass balance equations governing the pressure drop in the mushy zone. This solution is based on an evolving fine volume grid superimposed to a finite element mesh used for the heat flow computations. A few applications illustrate the effects of process and alloy parameters on the final porosity fraction.