Fundamentals of Solidification in Aluminum Castings

In this paper the foundation is laid for a fundamental understanding of what happens during solidification. This knowledge is then used to derive practical conclusions about commercial casting alloys. Important phase diagrams are given. These describe, in the form of easily read graphs, what phases form and the relationships between the phases. The non-equilibrium process of solidification is then discussed. The formation, growth and coarsening of dendrites is described and correlations given for secondary dendrite arm spacing (SDAS) as a function of local solidification time. Finally, segregation is considered and models which describe the segregation are reviewed. Example calculations are made for solidification paths in Al-Si casting alloys and suggestions are made to optimize casting alloy compositions.