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Öğe Drilling of a hybrid Al/SiC/Gr metal matrix composites(Springer London Ltd, 2012) Altunpak, Yahya; Ay, Mustafa; Aslan, SerdarThe present study investigates the influence of cutting parameters on cutting force and surface roughness in drilling of Al/20%SiC/5%Gr and Al/20%SiC/10%Gr hybrid composites fabricated by vortex method. The drilling tests are conducted with diamond-like carbon-coated cutting tools. This paper is an attempt to understand the machining characteristics of the new hybrid metal matrix composites. The results indicate that inclusion of graphite as an additional reinforcement in Al/SiCp reinforced composite reduces the cutting force. The cutting speed and its interactions with feed rate are minimum. Feed rate is the main factor influencing the cutting force in both composites. The surface roughness value is proportional with the increase in feed rate while inversely proportional with cutting speed in both composites. For all cutting conditions, Al/20%SiC/10%Gr composite has lower surface roughness values than Al/20%SiC/5%Gr composite. The surface is analyzed using scanning electron microscope.Öğe Effect of Aging Heat Treatment on Bending Strength of ?-Al2O3 Short Fiber Reinforced LM 13 Aluminum Alloy(TUBITAK, 2019) Altunpak, Yahya; Akbulut, Ve HatemIn this study, ?-Al2O3 short fibers (0%-30 %) reinforced Al-12Si (wt-%) LM-13 aluminum composites formed by gas pressure infiltration method were used. In the literatüre; the standard aging heat treatment of LM-13 aluminum alloy is given as solutionizing at 515 °C for 8 h. And aging at 171 °C for 12 h. Prior experiments on these composites have shown that this aging treatment was not sufficient to get the intermetallics, that to be precipitated during aging, could not be solved by the standard solution temperatures and times. For this purpose, different heat treatment parameters have been tried to clarify the effect of the reinforcing element on the matrix phase precipitation in these composites. The aim of the work was to study the effect of ?-Al2O3 short fibers and aging heat treatment on the bending strength of the composites. Unreinforced alloy and the composite samples have subjected to three-point bending tests and the shear strength values were measured. Measurement of bending strength with scanning electron microscopy studies show that the biggest value of bending strength increment for unreinforced and ?-Al2O3 short fiber reinforced LM13 alloys are very different. Initial studies have shown that the solution take-up temperature of 535 is ideal for maximum bending strength. For this reason, the composites and unreinforced alloy specimens were solution treated at 535 °C temperature for 8, 12, 16 and 20 hours and quenched in water at 20 °C. Aging was carried out at four aging temperatures of 151, 161, 171 and 181°C for a varying time of up to 22 h in air. The results revealed that at the optimized aging heat treatment conditions have given higher bending strength results when compared with standard aging treatment. For example, optimum heat treatment for 30 pct ?-Al2O3/ Al-12Si composite the optimum heat treatment was recorded as follows; solution treatment at 535°C for 20 hours and artificial aging at 151°C for 14 hours. The fracture surface investigations that performed by secondary electron images by scanning electron microscopy (SEM) showed that the fibers are bonded very well to the matrix and the phenomenon of fiber pull-out from the matrix is minimum at the optimum heat-treated composite samples. © 2019, TUBITAK. All rights reserved.Öğe The effect of aging heat treatment on the sliding wear behaviour of Cu-Al-Fe alloys(Elsevier Sci Ltd, 2009) Yaşar, Mustafa; Altunpak, YahyaAluminium bronze is one of the versatile wear resisting engineering materials that work under a corrosive environment with high stress. Alloys were produced by casting of C95200 and C95300 aluminium bronzes and aged. Wear behaviors, friction coefficient, and microstructure were investigated. The results indicated that a suitable aging treatment resulted in the formation of smaller alpha grains than their cast condition. These small alpha grains could improve the hardness and wear resistance of Cu-Al-Fe alloys. But with increasing aging temperature, the wear rate of the aged Cu-Al-Fe alloys initially decreased and then began to increase. (C) 2008 Elsevier Ltd. All rights reserved.Öğe Effect of alternative heat-treatment parameters on the aging behavior of short-fiber-reinforced 2124 al composites(Inst Za Kovinske Materiale I In Tehnologie, 2016) Altunpak, Yahya; Aslan, Serdar; Güler, Mehmet Oğuz; Akbulut, HatemThe 2124 Al alloy and a composite of the 2124 Al alloy reinforced with 20 % of volume fractions of delta-Al2O3 short fibers made by squeeze casting were subjected to controlled and systematic aging treatments. The materials were solution treated at (495, 525 and 555) degrees C. After quenching, the matrix alloy and the composite were artificially aged at (160, 170, 180 and 190) degrees C up to 36 h. The aging was monitored with hardness measurements and differential scanning calorimetry. The time required to reach the peak hardness of the composite matrix during a precipitation treatment was shorter than that for the unreinforced 2124 Al. An increase in the solution-treatment temperature resulted in an increase of the composite-matrix hardness. The delta-Al2O3-reinforced composite exhibits no grain-boundary melting, but appears to show incipient melting around short alumina fiber interfaces at temperatures above 525 degrees C. The highest HV value was obtained after solutionizing at 495 degrees C for 6 h, followed by water quenching and aging at 190 degrees C for 10 h for the unreinforced matrix alloy. In the case of the reinforced alloy the highest HV value was found after solutionizing at 555 degrees C for 6 h, quenching and aging at 170 degrees C for 12 h.Öğe Effect of electrode materials type on resistance spot welding of AISI 430 ferritic stainless steel(Trans Tech-Scitec Publications Ltd, 2017) Onsekiz, Murat; Altunpak, YahyaIn this study, AISI 430 ferritic stainless steel sheet with 0.6 mm thickness was joined by resistance spot welding using different electrode materials. The effects of electrode materials and welding parameters on the mechanical properties of welded samples are defined in terms of peak load. The hardness and tensile shear load bearing capacity of welded joint was determined and the microstructure of welded samples was also evaluated. The most suitable welding parameters for each electrode material were determined.Öğe The effect of plasma spraying on the microstructure and aging kinetics of the Al-Si matrix alloy and Al-Si/SiC composites(Springer, 2010) Altunpak, Yahya; Akbulut, Hatem; Üstel, FatihThe Al-Si (LM 13)-based matrix alloy reinforced with SiC particles containing 10, 20, and 30 vol.% SiC particles were spray-formed onto Al-Si substrates. The sprayed samples were directly subjected to a standard aging treatment (T551). From the experiments, it was observed that the high rate of solidification resulted in very fine silicon particles which were observed as continuous islands in the matrix and each island exhibited several very fine silicon crystals. Analysis showed that plasma-spraying caused an increased solid solubility of the silicon in the aluminum matrix. DSC measurements in the permanent mold-cast Al-Si matrix alloy and plasma-sprayed Al-Si matrix alloy showed that plasma-spraying causes an increase in the amount of GP-zone formation owing to the very high rate solidification after plasma-spraying. In the plasma-sprayed Al-Si/SiC composites GP zones were suppressed, since particle-matrix interfaces act as a sink for vacancies during quenching from high plasma process temperature. Introduction of SiC particles to the Al-Si age-hardenable alloy resulted in a decrease in the time required to reach plateau matrix hardness owing to acceleration of aging kinetics by ceramic SiC particles.Öğe Effects of aging heat treatment on machinability of alumina short fiber reinforced LM 13 aluminum alloy(Springer London Ltd, 2009) Altunpak, Yahya; Akbulut, HatemIn this paper, the surface integrity (Ra and Rmax) has been investigated with various aging heat treatment and machinability parameters in an aluminum-silicon based (LM-13) MMCs, produced by infiltration method. The composites have been subjected to heat treatment at different temperatures and times which was discussed in detail in an earlier publication (Altunpak and Akbulut, Teknoloji 8(4):331-339, 2005). In the milling of alumina short fiber reinforced LM-13 aluminum alloys, the surface integrity decreased when feed rate increased. It was found that increasing amount of fiber reinforcement and solutionizing temperature has a significant effect on the surface integrity and sub-surface damage of the materials. Increasing the solutionizing temperature and fiber reinforcement produced higher Ra and Rmax values. Microhardness measurement indicated that the sub-surface damage and the hardness increased by increasing the feed rate and fiber content.Öğe The Grey-based Taguchi method: optimisation of drilling of hybrid aluminum matrix composites(Polish Acad Sciences Inst Physics, 2017) Ay, Mustafa; Altunpak, Yahya; Hartomacıoğlu, SelimThe aim of this study was to investigate the influence of cutting parameters and effect of graphite rate on cutting force and surface roughness in drilling of Al/20% SiC/5% Gr, Al/20% SiC/7.5% Gr and Al/20% SiC/10% Gr hybrid composites, fabricated by vortex method. The drilling tests are conducted with diamond-like-carbon coated cutting tools. The Grey relational analysis based Taguchi optimization method was selected to determine the optimum cutting conditions. The results show that the spindle speed ( 4500 rpm), the rate of graphite (10%) and feed (0.1 mm/rev) were found to be significant parameters for surface roughness and cutting force. The predicted values from the developed model and experimental values are found to be very similar in this study.Öğe Mechanical properties of a squeeze-cast 2124 Al composite reinforced with alumina short fibre(Edp Sciences S A, 2017) Altunpak, Yahya; Akbulut, HatemThe tensile, flexural and fracture behaviours of alumina short fibre reinforced 2124 Al alloy produced by squeeze-cast method have been investigated. The composite and unreinforced alloys have been subjected to heat treatment at different temperatures and times. The highest yield strength, ultimate tensile strength and flexural strength values were obtained after solution treatment at 495 degrees C for the unreinforced alloy. The optimum mechanical properties of the composite material were obtained at 525 degrees C owing to better fibre-matrix interfacial bonding. The peak aging heat treatment conditions at which maximum hardness values are obtained do not provide maximum strength values in the composite. Increasing solution treatment temperature caused fibre decohesion from the matrix due to porosity formed at the fibre matrix interface.Öğe Wear behaviour of aged Cu-Be alloy under electrical sliding(Academic Journals, 2010) Altunpak, YahyaThe sliding friction and wear behaviors of aged Cu-Be alloy was studied in the presence of electrical current. Electrical sliding was performed between a Cu-Be pin and a flat surface of a hardened steel disk in ambient atmosphere. The effects of aging heat treatment, electrical current density on the friction and wear behavior were investigated. The microstructure and the worn surfaces of the aged Cu-Be alloy were also investigated by optical microscope, scanning electron microscope (SEM) and energy-dispersive spectroscopy (EDS). The results indicated that the aging treatment has affected the microstructure, hardness and wear resistance of Cu-Be alloy. The values of hardness for the alloy reached the peak hardness after an aging treatment at 330 degrees C for 3 h and over-aging occurred at higher temperature. Both the coefficient of friction and wear loss increased when small electrical current was applied and decreased as the electrical current density increased. Adhesive wear and abrasive wear were the dominant mechanisms during the electrical sliding processes. The alloy treated at 330 degrees C for 3 h exhibited much better wear resistance.