Cellular growth of single-phase Zn–Ag alloys unidirectionally solidified

• The scale of cellular microstructures is fundamental for properties of castings.
• Cellular spacing is correlated with the cooling rate by an experimental growth law.
• The proposed law encompasses steady-state and transient solidification regimes.

Transient unidirectional solidification experiments have been carried out with a single-phase Zn–Ag alloy under cooling rates in the range of 0.1–40 K s−1. The resulting macrostructure is shown to be typified by columnar grains aligned along the heat flow direction and the microstructure is characterized by a cellular morphology along the entire casting length with no evidence of cellular/dendritic transition. A regular to plate-like cells transition is shown to occur for cooling rates higher than 10K s−1. Experimental results from the literature on the cellular growth of single-phase Zn–Ag alloys in steady-state solidification conditions are compared with the results of the present investigation. An experimental growth law relating the cell spacing with the cooling rate is proposed, which is shown to be able to represent both the steady-state and transient growth regimes of single-phase Zn–Ag alloys. The Bouchard–Kirkaldy model is shown to be the only theoretical growth model that matches the cellular experimental scatters in both solidification regimes.