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The Al-5.5Zn-2.5Mg (wt pct) ternary alloy was prepared using a vacuum melting furnace and a casting furnace. Five samples were directionally solidified upwards at a constant temperature gradient (G = 5.5 K/mm) under different growth rates (V = 8.3-165 lm/s) in a Bridgman-type directional solidification furnace. The primary dendrite arm spacing, k 1 , secondary dendrite arm spacing, k 2 , and microhardness, HV, of the samples were measured. The effects of V on k 1 , k 2 and HV properties of the Al-Zn-Mg alloy were studied by microstructure analysis and mechanical characterization. Microstructure characterization of the alloys was carried out using optical microscopy, scanning electron microscopy, wavelength-dispersive X-ray fluorescence spectrometry, and energy dispersive X-ray spectroscopy. From the experimental results, it is found that the k 1 , k 2 values decrease, but HV values increase with the increase in V, and HV values decrease with the increase in k 1 and k 2 . Dependencies of dendritic spacing and microhardness on the growth rate were determined using linear regression analysis. The growth rate, microstructure, and Hall-Petch-type relationships obtained in this work have been compared with the results of previous studies.

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