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 (d 1) has been correlated with the growth rate (R), the temperature gradient in the liquid immediately ahead of the solid/liquid interface (G L) and the bulk alloy composition (C 0). Similar correlations were made for the secondary arm spacing (d 2). In addition,d 2 values were found to be related to the local solidification time (t f). It was observed that the relationshipR k G m d 1 =K, the primary arm spacing, andR l d 2 =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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Abbreviations
- d 1 :
-
Primary arm spacing, μm
- d 2 :
-
Secondary arm spacing, μm
- R :
-
Growth rate, μm sec−1
- G L :
-
Temperature gradient ahead of the solid/ liquid interface, ° C μm−1 or ° C cm−1
- C 0 :
-
Bulk alloy composition, wt%
- K,K′,K″:
-
Constants
- k, m, l, n :
-
Exponents
- t f :
-
Local solidification time, sec.
- ΔT 0 :
-
Freezing interval atC 0, ° C
- L :
-
Distance between eutectic front and the plane of dendrite tips, μm
- r t :
-
Tip radius of dendrites, μm
- D :
-
Diffusion coefficient of solute in the melt, cm2sec−1 or μm2sec−1
- Г :
-
Gibb-Thomson coefficient, °C. cm or °C μm
- k 0 :
-
Distribution or partition coefficient
- K T :
-
Thermal diffusivity
- P s :
-
Solutal Peclet number
- P t :
-
Thermal Peclet number
- R t :
-
Thermal Rayleigh number
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Tunca, N., Smith, R.W. Variation of dendrite arm spacing in Al-rich Zn-Al off-eutectic alloys. J Mater Sci 23, 111–120 (1988). https://doi.org/10.1007/BF01174041
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DOI: https://doi.org/10.1007/BF01174041