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Dendrite spacing in unidirectionally solidified Al-Cu alloy
Authors:An Geying  Liu Lixin
Institution:

Department of Metallic Materials and Technology, Harbin Institute of Technology, Harbin, People's Rep. of China

Abstract:Directional solidification experiments have been carried out to study the variation in primary and secondary arm spacings with solidification parameters in the Al-Cu system. It is found that the primary arm spacing Z1 obeys the common correlation Z1 = KG-aV-b in the high velocity regime or low temperature gradient regime, where a and b are constants, the value of K included the composition dependence, G is the temperature gradient in the liquid and V the growth rate; however, it does not obey this correlation for the low velocity regime or high temperature gradient regime but goes through a maximum or a catastrophe as a function of V or G at V = Vcs/k or G = kGcs, where k is the equilibrium distribution coefficient, and Vcs and Gcs are the critical velocity and temperature gradient at the limit of constitutional undercooling respectively. The initial secondary arm spacings Z20 are nearly independent of G and mainly depended on V, Z20 = 0.016 V-0.54 (mm). The secondary arm spacing Z2 tends to c oarsen with time and thus is a function of coarsening time tf, Z2 = 0.016t0.34f (mm). Theoretical analyses of the primary arm spac ing and the initial secondary arm spacing have been proposed, and the derived relationships agree reasonably well with the above experimental results.
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