Effect of Growth Rate on the Microstructure and Microhardness in a Directionally Solidified Al-Zn-Mg Alloy
Abstract
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 μm/s) in a Bridgman-type directional solidification furnace. The primary dendrite arm spacing, λ 1, secondary dendrite arm spacing, λ 2, and microhardness, HV, of the samples were measured. The effects of V on λ 1, λ 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 λ 1, λ 2 values decrease, but HV values increase with the increase in V, and HV values decrease with the increase in λ 1 and λ 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.
- Publication:
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Metallurgical and Materials Transactions A
- Pub Date:
- June 2016
- DOI:
- 10.1007/s11661-016-3484-9
- Bibcode:
- 2016MMTA...47.3040A