Correlation between unsteady-state solidification conditions, dendrite spacings, and mechanical properties of Al-Cu alloys

The wide range of operational conditions existing in foundry and casting processes generates as a direct consequence a diversity of solidification microstructures. Structural parameters such as grain size and interdendritic spacings are strongly influenced by the thermal behavior of the metal/mold system during solidification, imposing, as a consequence, a close correlation between this system and the resulting microstructure. Mechanical properties depend on the microstructural arrangement defined during solidification. Expressions correlating the mechanical behavior with microstructure parameters should be useful for future planning of solidification conditions in terms of a determined level of mechanical strength, which is intended to be attained. In the present work, analytical expressions have been developed describing thermal gradients and tip growth rate during one-dimensional unsteady-state solidification of alloys. Experimental results concerning the solidification of Al-4.5 wt pct Cu and Al-15 wt pct Cu alloys and dendritic growth models have permitted the establishment of general expressions correlating microstructure dendrite spacings with solidification processing variables. The correlation of these expressions with experimental equations relating mechanical properties and dendrite spacings provides an insight into the preprogramming of solidification in terms of casting mechanical properties.