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    Effect of Growth Rate on the Microstructure and Microhardness in a Directionally Solidified Al-Zn-Mg Alloy
    (SPRINGER, 2016) Acer, Emine; Cadirli, Emin; Erol, Harun; Gunduz, Mehmet
    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 mu m/s) in a Bridgman-type directional solidification furnace. The primary dendrite arm spacing, lambda (1), secondary dendrite arm spacing, lambda (2), and microhardness, HV, of the samples were measured. The effects of V on lambda (1), lambda (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 lambda (1), lambda (2) values decrease, but HV values increase with the increase in V, and HV values decrease with the increase in lambda (1) and lambda (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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    Effect of Growth Velocity and Zn Content on Microhardness in Directionally Solidified Al-Zn Alloys
    (Univ Fed Sao Carlos, Dept Engenharia Materials, 2018) Acer, Emine; Cadirli, Emin; Erol, Harun; Kaya, Hasan; Sahin, Mevlut; Gunduz, Mehmet
    In this study, Al-xZn (x=1, 3, 5, 7, 10 and 20 wt. %) alloys were prepared using metals of 99.99% high purity in the vacuum atmosphere. These alloys were directionally solidified upward with a constant temperature gradient, G (10.3 K/mm) and different growth velocities (V) between 8.25 and 165 mu m/s in the directional solidification apparatus. The experimental results have revealed that with the increase of the growth velocity of the melts from 8.25 mu m/s to 165 mu m/s, the microstructures undergo a transition from cellular/cellular dendritic morphology to coarse dendritic form for each composition (Zn content, C-o). The measurements of microhardness (HV) of the specimens were performed by using a microhardness test device. The dependence of HV on V and C(o )was analyzed, and it has been found that with increasing the V and C-o the HV increases. Relationships between HV-V and HV-C-o were obtained by linear regression analysis, and the experimental results were compared with the results of previous similar works.
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    Effect of heat treatment on the microstructures and mechanical properties of Al-5.5Zn-2.5Mg alloy
    (ELSEVIER SCIENCE SA, 2016) Acer, Emine; Cadirli, Emin; Erol, Harun; Kirindi, Talip; Gunduz, Mehmet
    The Al-5.5 Zn-2.5 Mg (wt%) ternary alloy was prepared using a vacuum melting furnace and a casting furnace. Microstructural and mechanical properties of the alloy were investigated as-cast and under heat-treated conditions. To investigate the effect of heat treatment, numerous designed Al-5.5 Zn-2.5 Mg samples were homogenized under different conditions and then aged under different regimes. The effects of heat treatment on the microstructures were examined by OM, SEM, and TEM, and mechanical properties of the Al-Zn-Mg alloy were studied. A good combination of high microhardness and reasonable tensile strength were obtained by successive and suitable heat treatments. After aging for 24 h at 150 degrees C, the peak microhardnes and tensile strength values were achieved as 157 MPa and 188.8 MPa, respectively. The microscopic fracture surfaces of the aged samples under different homogenization and aging conditions were observed using scanning electron microscopy. Fractographic analysis of the tensile fracture surfaces shows that the type of fracture changed significantly from ductile to more ductile depending on the aging regime. (C) 2016 Elsevier B.V. All rights reserved.