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    EFFECTS OF THE ARTIFICIAL-AGING TEMPERATURE AND TIME ON THE MECHANICAL PROPERTIES AND SPRINGBACK BEHAVIOR OF AA6061
    (INST ZA KOVINSKE MATERIALE I IN TEHNOLOGIE, 2015) Polat, Aytekin; Avsar, Mustafa; Ozturk, Fahrettin
    In this study, the effects of the artificial-aging temperature and time on the mechanical properties and springback behavior of AA6061 are investigated. The results reveal that the yield strength, the tensile strength and the elongations decreased with the increasing artificial-aging temperature, but increased with the increasing artificial-aging time up to the peak age. The springback of the alloy increased significantly with the increasing artificial-aging time at the artificial-aging temperature ranging from 160 degrees C to 180 degrees C and decreased with the artificial-aging time at 200 degrees C. The springback angle in the as-received condition is lower than in all the aged conditions.
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    Effects of the artificial-aging temperature and time on the mechanical properties and springback behavior of AA6061
    (Institute of Metals Technology, 2015) Polat, Aytekin; Avsar, Mustafa; Ozturk, Fahrettin
    In this study, the effects of the artificial-aging temperature and time on the mechanical properties and springback behavior of AA6061 are investigated. The results reveal that the yield strength, the tensile strength and the elongations decreased with the increasing artificial-aging temperature, but increased with the increasing artificial-aging time up to the peak age. The springback of the alloy increased significantly with the increasing artificial-aging time at the artificial-aging temperature ranging from 160 °C to 180 °C and decreased with the artificial-aging time at 200 °C. The springback angle in the as-received condition is lower than in all the aged conditions.
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    Influence of sodium silicate concentration on structural and tribological properties of microarc oxidation coatings on 2017A aluminum alloy substrate
    (ELSEVIER SCIENCE SA, 2010) Polat, Aytekin; Makaraci, Murat; Usta, Metin
    In this paper, thick and hard oxide coatings resistant to wear were produced on 2017A-T6 Al alloy by the microarc oxidation (MAO) technique in an alkali electrolyte consisting of different sodium silicate concentrations (0-8 g/l). The coatings were characterized by means of optical microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD) and surface profilometry. Microhardness, scratch adhesion and pin-on-disk sliding wear tests were also performed to evaluate the tribological properties of the coatings. The influence of sodium silicate concentration on the structural and tribological properties of the MAO coatings was discussed. Results reveal that increasing sodium silicate concentration from 0 to 8 g/l in the electrolyte caused an increase in the electrolyte conductivity (from 7.71 to 18.1 mS/cm) and a decrease in positive final voltage (from 627 to 590 V) in the MAO process. In response to the increase in sodium silicate concentration, the thickness, surface roughness (R(a)) and critical load (L(c)) corresponding to adhesive failure of the coatings were increased simultaneously from 74 to 144 mu m, and 4.4 to 6.58 mu m, and 127.76 to 198.54 N, respectively. At the same time, the phase structure and composition of the coatings also varied by the participation of silicate ions in the reactions and their incorporation into the coating structure. Moreover, it was observed that the coating formed in the low sodium silicate concentration (4 g/l) had higher surface hardness (2020 HV) and improved wear resistance than the one (1800 HV) formed in the high sodium silicate concentration (8 g/l). The coatings produced in three different electrolytic solutions provided an excellent wear resistance and a load carrying capacity compared to the uncoated aluminum alloy. (C) 2010 Elsevier B.V. All rights reserved.
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    Mechanical and microstructural evaluations of hot formed titanium sheets by electrical resistance heating process
    (ELSEVIER SCIENCE SA, 2013) Ozturk, Fahrettin; Ece, Remzi Ecmel; Polat, Naki; Koksal, Arif; Evis, Zafer; Polat, Aytekin
    In this study, effect of temperature in the electrical resistance heating process on mechanical properties and microstructures of commercially pure titanium grade 2 (CP2) and Ti-6Al-4V (T64) alloy sheets was investigated. Sheets were successfully heated by the electric resistance heating process, and their mechanical properties and microstructures were evaluated. Ductilities of both materials were increased significantly after 400 degrees C. Results indicate that no significant change was observed in grain sizes and microhardness of the materials. XRD analysis revealed that presence of secondary phases regarding oxidation of Ti was observed for 164 alloy above the manufacturer specified temperature ranges. However, no secondary phase was observed even above the manufacturer specified temperature ranges for CP2. (c) 2013 Elsevier B.V. All rights reserved.
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    The Effects of Strain Rate and Temperature on the Deformation Behavior of Cold-Rolled TRIP800 Steel
    (WILEY-V C H VERLAG GMBH, 2012) Polat, Aytekin
    In the present study, the influences of temperature and strain rate on the deformation behavior of cold-rolled TRIP800 steel were investigated. Microstructural observation and tensile tests were performed and volume fractions of retained austenite were measured at various temperatures and strain rates. The results reveal that both temperature and strain rate affect the volume fractions of retained austenite that transforms into martensite. The strain-induced transformation of retained austenite is retarded with increasing temperature and the retained austenite becomes more stable against straining. The amount of retained austenite that transforms into martensite is not influenced significantly by strain rate. The variation in mechanical properties with temperature and strain rate was related to the effects of dynamic strain aging, tempering of banite, high temperature softening, and the volume fractions of retained austenite.