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    The effect of Ni addition on microstructure and mechanical properties of cast A356 alloy modified with Sr
    (Redakcia Kovove Materialy, 2021) Ozyurek, D.; Yildirim, M.; Yavuzer, B.; Simsek, I; Tuncay, T.
    In this study, casting A356 alloy was pre-alloyed with Ni, and the modification process with Sr was applied by the casting method. The role of Ni on the microstructural and mechanical properties of the produced A356-Ni alloys was investigated. The produced alloys were naturally aged at room temperature for 24 h and artificially aged at 170 degrees C for 10 h. Optical microscopy (OM), scanning electron microscopy (SEM), and X-ray diffractometer were used in microstructure studies of the A356-Ni alloys. Tensile tests and hardness measurements were carried out to determine mechanical properties. Statistical analysis of Weibull distribution on the tensile test results revealed that the characteristic ultimate tensile strength increased due to increasing the amount of alloying elements, while the characteristic percentage elongation is decreased. This was because Al-Si-Fe intermetallic decomposition and Al-Si-Fe-Ni intermetallics were formed, primarily, 0.5 and 1.0 % Ni addition. It was also determined that the Al-Si-Fe-Ni intermetallics with a morphology non-sharp corners formed more homogeneous in the microstructure. But in the A356 alloys with the addition of 1.5 % Ni, Al-Si-Fe-Ni intermetallics are formed in coarser morphology. In A356 alloys, aluminium dendrites, Al-Si eutectic between dendrites, Mg2Si precipitates are formed in the structure by ageing. Depending on the amount of Ni added to the A356 alloy, the tensile strength of the alloys containing 0.5 and 1.0 % Ni is increased.
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    Investigation of the electrochemical corrosion properties of high-energy milled Ti6Al4V alloy in simulated body fluid environment
    (Taylor & Francis Ltd, 2019) Simsek, I; Ozyurek, D.
    In this study, the electrochemical corrosion properties of high-energy milled Ti6Al4V alloy are investigated. The Ti6Al4V alloy is produced by high-energy milling at different milling times in mechanical milling device as 15-120min. Produced alloy powders are cold-pressed under 620MPa pressure and sintered at 1300 degrees C temperature and characterised by scanning electron microscopy (SEM), X-ray diffraction, hardness and density measurements. Corrosion tests are conducted in simulated body fluid at 37 degrees C body temperature. Results showed that the average particle size of the powder is reduced, and the hardness of the alloy is increased with the increasing milling time. It is determined that the corrosion properties of the alloys change by the high-energy milling time, and the corrosion rate increases by the decreasing particle size of the powder. SEM examination of the corroded surfaces after potentiodynamic polarisation tests revealed that pitting formation tendency of the alloys on the alloy surface increases by the increasing high-energy milling time.
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    Relationship between Al2O3 Content and Wear Behavior of Al+2% Graphite Matrix Composites
    (De Gruyter Poland Sp Z O O, 2020) Simsek, D.; Simsek, I; Ozyurek, D.
    In this study, the microstructure and wear behaviours of aluminium composites, reinforced with different amounts of (3-12%) Al2O3 and 2% (% vol.) graphite were investigated. The Al2O3 and graphite were added to Al matrix and mechanically alloyed for 60 minutes. Subsequently, the mechanically alloyed powders were pressed under 700 MPa pressure and sintered at 600 degrees C for 120 minutes. The produced aluminium composites were characterized by microstructure, scanning electron microscope (SEM), X-ray diffraction (XRD), density and hardness measurements. Afterwards, wear tests were carried out on a block on-ring type wear testing device, under three different loads and four different sliding distances. As a result, the hardness and density of composites were observed to increase due to the increase in the amount of reinforcement in aluminium composites. The highest hardness and density values were obtained in composite material containing 12% Al2O3. The wear tests, the lowest weight loss was also obtained in composite containing 12% Al2O3.