· Técnicas de simulación avanzadas ·
F. Yi,* H. D. Brody* and J. E. Morral**
* University of Connecticut, USA, ** The Ohio State University, USA
67th World Foundry Congress
Numerical simulations of solute redistribution and microstructure evolution
during solidification, post-solidification cooling, and solution heat treatment
have been extended to multi-phase, multi-component Al-Si-Cu-Mg alloys.
The basic models that have been applied to binary and ternary systems
have been modified to handle the extra degrees of freedom in quaternary
and higher order systems, which are more representative of commercial
casting alloys.
During solidification Si and Mg diffusion is extensive and microsegregation
of Si and Mg in the dendrite cores at the end of solidification is negligible.
Diffusion of Cu through the dendrite cores controls the extent of
microsegregation of Cu in the as-solidified alloy. The presence of small
amounts of Mg enhances diffusion of Cu, and the diffusivity of Cu in multiphase
interdendritic regions is several multiples of the diffusivity through
the single-phase dendrite cores.
Substantial solute redistribution occurs during post-solidification cooling in
sand or permanent molds. Si, in particular, diffuses from dendrite cores to
the interdendritic regions as the solubility of Si in the interdendritic α-Al
phase decreases sharply with decreasing temperature.
During solution heat treatment the redistribution of solute that occurs
during post-solidification cooling is reversed quickly. The nonequilibrium
amounts of θ-phase and Q-phase that are distributed in the interdendritic
regions between secondary dendrite arms at the end of solidification are
reduced to their equilibrium amounts within a few hours. Nonequilibrium
phases distributed in the grain boundaries and between primary dendrite
branches require ten or more hours to reduce to their equilibrium amounts.
