Abstract
Primary and secondary arm spacings were measured in various unidirectionally solidified Al-rich Zn-Al off-eutectic alloys. In order to determine the influence of convective processes on dendrite arm spacings, freezing was carried out both vertically upwards and downwards, and over a wide range of growth rates. The primary arm spacing parameter (d1) has been correlated with the growth rate (R), the temperature gradient in the liquid immediately ahead of the solid/liquid interface (GL) and the bulk alloy composition (C0). Similar correlations were made for the secondary arm spacing (d2). In addition,d2 values were found to be related to the local solidification time (tf). It was observed that the relationshipRkGmd1 =K, the primary arm spacing, andRld2 =K′, secondary arm spacing, were obeyed (K andK′ are constants). In addition, the effects of solute gradient-induced convection on the extent of macrosegregation in these alloys have been determined as a function of composition and growth rate.
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