Directional solidification and physical properties measurements of the zinc-aluminum eutectic alloy

Abstract

Zn-5wt% Al eutectic alloy was directionally solidified with different growth rates (5.32–250.0 μm/s) at a constant temperature gradient of 8.50 K/mm using a Bridgman-type growth apparatus. The values of eutectic spacing were measured from transverse sections of the samples. The dependences of the eutectic spacing and undercooling on growth rate are determined as λ=9.21V ^−0.53 and ΔT=0.0245V ^0.53, respectively. The results obtained in this work were compared with the Jackson-Hunt eutectic theory and the similar experimental results in the literature. Microhardness of directionally solidified samples was also measured by using a microhardness test device. The dependency of the microhardness on growth rate is found as Hv=115.64V ^0.13. Afterwards, the electrical resistivity (r) of the casting alloy changes from 40×10⁻⁹ to 108×10⁻⁹ Ω·m with the temperature rising in the range of 300–630 K. The enthalpy of fusion (ΔH) and specific heat (C _p) for the Zn-Al eutectic alloy are calculated to be 113.37 J/g and 0.309 J/(g·K), respectively by means of differential scanning calorimetry (DSC) from heating trace during the transformation from liquid to solid.

Keywords

eutectic alloys / directional solidification / microhardness / electrical conductivity / enthalpy / specific heat

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