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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 growth velocity on microstructure and mechanical properties of directionally solidified 7075 alloy
    (Taylor & Francis Ltd, 2020) Cadirli, Emin; Nergiz, Emel; Kaya, Hasan; Buyuk, Ugur; Sahin, Mevlut; Gunduz, Mehmet
    7075 alloys were prepared using metals of 99.99% high purity in the vacuum atmosphere. These alloys were directionally solidified upwards under various growth velocities (8.3-166.0 mu m/s) using a Bridgman-type directional solidification furnace. Dendritic spacings (lambda(1), lambda(2)) and microhardness (HV) were measured from both longitudinal and transverse sections of the samples. Ultimate tensile strength (sigma(U)) and yield strength (sigma(y)) of the solidified samples at room temperature were examined. The HV increased from 75.2 to 112.8 MPa, the sigma(U) increased from 155.8 to 210.1 MPa, and the sigma(y) increased from 198.4 to 319.8 MPa with increasing growth velocity from 8.3 to 166.0 mu m/s. Exponent values of the V for the lambda(1), lambda(2), HV, sigma(U) and sigma(y) were calculated as 0.27, 0.41, 0.05, 0.11 and 0.15, respectively. The results show that the hot tearing in the 7075 alloy is caused by the fracture of dendrites structures.
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    Effect of heat treatments on the microhardness and tensile strength of Al-0.25 wt.% Zr alloy
    (ELSEVIER SCIENCE SA, 2015) Cadirli, Emin; Tecer, Hicran; Sahin, Mevlut; Yilmaz, Elif; Kirindi, Talip; Gunduz, Mehmet
    In the present work, the effect of heat treatments on the microhardness and tensile properties of the Al-0.25 Zr (wt.%) alloy have been investigated. The Al-0.25 Zr (wt.%) alloy was melted in a vacuum furnace, and the molten alloy was poured into crucibles held in a hot filing furnace. Then, the samples were directionally solidified from bottom to top and aged isothermally and isochronally in a muffle furnace. Aging was performed in two ways: using a wide range of temperatures (350-600 degrees C) with a constant aging time (100 h) and a wide range of aging times (3-240 h) with a constant temperature (400 degrees C). The dependence of the microhardness (HV) and ultimate tensile strength (sigma(UTS)) on the aging temperatures and aging times was determined. According to the experimental results, the HV and sigma(UTS) values of the aged samples increase at a certain aging temperature and aging time values, reaching peak values at specific temperatures and aging times. The microhardness and ultimate tensile strength decreased with further increase of aging temperatures and aging times. The microscopic fracture surfaces of the aged samples under different 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 brittle depending on the aging times. Transmission electron microscopy was also used to characterize the precipitation processes in an Al-0.25 Zr (wt.%) alloy aged at 400 degrees C for 120 h. (C) 2015 Elsevier B. V. All rights reserved.
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    Effects of Aging Temperature, Time, and Pre-Strain on Mechanical Properties of AA7075
    (Univ Fed Sao Carlos, Dept Engenharia Materials, 2019) Kilic, Suleyman; Kacar, Ilya; Sahin, Mevlut; Ozturk, Fahrettin; Erdem, Oguz
    Aluminum alloys of the 7xxx series (AA7075) are preferred in the aerospace and automotive industries due to their low densities, high strength, good corrosion resistance properties. Additionally, these alloys show the most effective aging properties among aluminum alloys. For this reason, it is very important to determine the most appropriate aging parameters for microstructural development. Literature review reveals that the effect of pre-strain on springback has not been studied yet. In this study, the effects of aging temperature, time, and pre-strain on mechanical properties are investigated for AA7075. Precipitates present in solid solutions of AA7075 and their effects are examined. Results reveal that MgZn2 precipitation is not observed at aging temperatures of 120 and 160 degrees C. After the formation of MgZn2 precipitates, microstructure becomes softer when aging continues at a higher temperature or longer period of time. It is clearly seen that pre-strain causes Portevin-Le Chatelier (PLC) effect after aging at 120 and 160 degrees C for aging times of 30 and 90 minutes.
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    Investigation of mechanical, electrical, and thermal properties of a Zn-1.26 wt% Al alloy
    (SPRINGER, 2011) Cadirli, Emin; Sahin, Mevlut
    Zn-1.26 wt% Al alloy was directionally solidified upward with a constant growth rate (V = 16.6 mu m/s) in a wide range of temperature gradients (1.94-5.15 K/mm) and with a constant temperature gradient (G = 5.15 K/mm) in a wide range of growth rates (8.3-500 mu m/s) with a Bridgman-type directional solidification furnace. The microhardness (HV) and tensile strength (sigma) of alloy were measured from directionally solidified samples. The dependency of the microhardness, tensile strength for directionally solidified Zn-1.26 wt% Al alloy on the solidification parameters (G, V) and microstructure parameters (lambda(1), lambda(2)) were investigated and the relationships between them were experimentally obtained using regression analysis. According to present results, the microhardness and tensile strength of directionally solidified Zn-1.26 wt% Al alloy increase with increasing solidification processing parameters and decrease with the microstructure parameters. Variations of electrical resistivity (rho) with the temperature in the range of 300-650 K were also measured using a standard dc four-point probe technique for cast samples. The enthalpy of fusion and specific heat for same alloy was also determined by means of differential scanning calorimeter (DSC) from heating trace during the transformation from solid to liquid.
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    Investigation of the Some Physical Properties of the Directionally Solidified Al-Cu-Co Ternary Eutectic Alloy
    (SPRINGER INDIA, 2015) Cadirli, Emin; Yilmazer, Izzettin; Sahin, Mevlut; Kaya, Hasan
    The Al-23.9% Cu-1.2% Co (wt%) ternary eutectic alloy was prepared using a vacuum melting furnace and a casting furnace. The samples were directionally solidified upwards at a constant growth velocity (18.8 mu m/s) under different temperature gradients (1.23-5.66 K/mm) and at a constant temperature gradient (5.66 K/mm) under different growth velocities (8.3-166 mu m/s) in a Bridgman-type directional solidification furnace. The dependence of the eutectic spacing on the solidification parameters (temperature gradient and growth rate) and that of the microhardness and compressive strength on the eutectic spacing and solidification parameters were investigated. The electrical resistivity measurements of the studied alloy were performed and the temperature coefficient of the resistivity was calculated from the curve of the resulting rho-Icurrency sign plot. The thermal conductivities of the sample grown at a constant temperature gradient and growth rate were obtained using the Wiedemann-Franz and Smith-Palmer equations.
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    Mechanical properties of directionally solidified lead-antimony alloys
    (SPRINGER, 2011) Sahin, Mevlut; Kaya, Hasan
    The Pb-17w% Sb alloy was directionally solidified under two solidification conditions: with different temperature gradients (G=0.93-3.67 K/mm) at a constant growth rate (V=17.50 mu m/s) and with different growth rates (V=8.3-497 mu m/s) at a constant temperature gradient (G=3.67 K/mm) in a Bridgman furnace. Microstructure parameters, such as primary dendrite arm spacing (lambda(1)), secondary dendrite arm spacing (lambda(2)), and dendrite tip radius (R), were measured. The microhardness (Hv) and ultimate tensile strength (sigma) of the directional solidification samples were also measured. The influences of solidification and microstructure parameters on Hv and sigma were investigated. The results obtained in this work were compared with similar experimental researches in literatures. It is shown that the Hv and sigma values increase with the increase of G and V, but decrease with the increase of lambda(1), lambda(2), and R.
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    SOLIDIFICATION CHARACTERISTICS AND MICROSTRUCTURAL EVOLUTION OF Zn-1.26 wt.% Al ALLOY
    (WORLD SCIENTIFIC PUBL CO PTE LTD, 2011) Sahin, Mevlut; Cadirli, Emin
    Zn-1.26 wt.% Al alloy was directionally solidified upward with a constant growth rate (V 16.6 mu m/s) in a wide range of temperature gradients (G = 1.94-5.15 K/mm) and with a constant temperature gradient (G = 5.15 K/mm) in a wide range of growth rates (V = 8.3-500 mu m/s) with a Bridgman-type directional solidification furnace. Microstructure parameters, the primary dendrite arm spacing (lambda(1)), secondary dendrite arm spacing (lambda(2)) and dendrite tip radius (R), were measured and expressed as functions of G and V by using a linear regression analysis method. It was found that the values of lambda(1), lambda(2) and R decrease with increasing values of V and G. The experimental results were compared with the main predictive theoretical and experimental works for dendritic spacings.
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    The Effect of Growth Rate on the Microstructure and Mechanical Properties of 7020 Alloys
    (Springer, 2022) Kaya, Hasan; Buyuk, Ugur; Cadirli, Emin; Sahin, Mevlut; Gunduz, Mehmet
    The 7020 aluminum alloy is one of the hardenable Al-Zn-Mg based alloys, which are a family of high strength aluminum alloys. These 7020 alloys are commonly used in the aircraft and automotive industries. The microstructural changes have a significant impact on the mechanical properties of binary and multi-component alloys. For this reason, 7020 aluminum alloys were prepared with different growth rates on account of the changes in the microstructures; thus, directionally solidification processes were actualized with a Bridgman furnace at five various growth rates (V = 8.3-166.0 mu m/s) and at constant temperature gradient (G = 8.3 K/mm). Microhardness (HV), ultimate tensile strength (sigma(U)) and yield strength (sigma(y)) of the solidified alloys were determined. The HV increased from 758.8 to 917.1 N/mm(2), the sigma(U) from 125.4 to 208.1 N/mm(2) and the sigma(y) from 133.7 to 230.8 N/mm(2) with an increase in growth rate from 8.3 to 166.0 mu m/s.
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    The effects of temperature gradient and growth rate on the microstructure of directionally solidified Sn-3.5Ag eutectic solder
    (SPRINGER, 2012) Sahin, Mevlut; Cadirli, Emin
    The mechanical properties (microhardness, tensile strength) of alloys are controlled by their microstructure, which depends strongly on temperature gradient (G) and growth rate (V). Thus, it is important to understand the relationships among G, V and microstructure (rod eutectic) of Sn-Ag solders. The Sn-3.5 wt% Ag eutectic alloy was directionally solidified upward with a constant growth rate, V (16.5 mu m/s) at different temperature gradients, G (1.43-4.28 K/mm) and with a constant temperature gradient, G (3.93 K/mm) at different growth rates, V (8.3-500 mu m/s) in a Bridgman-type directional solidification furnace. The rod spacings (lambda) have been measured from both longitudinal section (parallel to the growth direction, lambda(L)) and transverse section (perpendicular to the growth direction, lambda(T)) of the samples. The undercooling values (Delta T) were calculated by using V, lambda and system parameters (K-1 and K-2). It was found that the values of lambda (lambda(T), lambda(L)) decrease while V and G are increasing. The relationships between rod spacing and solidification parameters (G and V) were obtained by linear regression analysis. The dependences of eutectic spacings lambda on undercooling (Delta T) are also analyzed. lambda V-2, lambda Delta T, Delta TV-0.5 and Delta TG(-0.5) values were determined by using lambda, Delta T, V and G values. The results obtained in this work are compared with the Jackson-Hunt eutectic theory and the similar experimental works. The experimental lambda V-2(T) value (159.3 mu m(3)/s) is slightly lower than the result 174.6 mu m(3)/s calculated from Jackson-Hunt eutectic theory.