Primary cellular/dendritic spacing selection of Al-Zn alloy during unidirectional solidification

Al-4.95 wt% Zn alloy is directionally solidified with Bridgman apparatus to investigate response of cellular/dendritic microstructures and primary spacing to the variation of growth velocity. The results show that, with increasing growth rate, there exist a transition from dendrite to cell and a wide distribution range in primary cellular/dendritic spacing. The maximum, λ_max, minimum, λ_min, and average primary spacing, λ̄, as functions of growth rate, V, can be given by λ_max = 4578V^-0.697, λ_min = 1315.7V^-0.6543, λ̄ = 3084.5V^-0.6982, respectively. The experimental results are compared with the Hunt-Lu model, and a reasonable agreement is found.