Wear Behaviour of SiC reinforced 2618 Al matrix composites

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Alüminyum alaşımları arasında, 2618 alüminyum alaşımı yüksek sıcaklık uygulamaları için (özellikle uçak motor parçası) geliştirilen Al-Cu-Mg-Fe-Ni içeren ısıl işlemle sertleştirilebilir bir dövme alüminyum alaşımıdır. Bu alaşımda bulunan Fe ve Ni elementleri sıcaklık altında mikroyapısal kararlılık sağlayarak alaşımın 200 °C’ye kadar mukavemetini korumaktadır. Bu çalışmada, sıkıştırma döküm yöntemi ile üretilmiş olan % 50 hacim oranında SiC partikül takviyeli döküm halindeki ve yaşlandırılmış durumdaki 2618 alüminyum matrisli kompozitin kuru kayma aşınma davranışları incelenmiştir. Kompozitlerin oda sıcaklığı mekanik özellikleri sertlik ve darbe deneyleri ile belirlenmiştir. % 50 SiC içeren 2618 aluminyum matrisli kompozitin sertliği yaşlandırma işlemi ile % 5 oranında artarken darbe direnci ise yaklaşık olarak % 12 oranında azalmıştır. Kompozitlerin aşınma davranışları ileri-geri aşınma deneyleri ile incelenmiştir. İleri-geri aşınma deneyleri 1.5-6.0 N yük aralığında, 0.02 m/s ve 0.09 m/s olmak üzere iki farklı kayma hızında Al2O3 topun sürtünmesi ile yapılmıştır. Aşınma deneyleri sonunda SiC ile takviye edilmiş 2618 alüminyum matrisli kompozitin döküm haline kıyasla, yaşlandırma ısıl işlemi ile aşınma direncinin düşük test yüklerinde ve yüksek kayma hızlarında değişmediği, ancak yüksek test yüklerinde ve düşük kayma hızlarında ise arttığı tespit edilmiştir.   Anahtar Kelimeler: Alümyum alaşımı, aşınma, kompozit, SiC.In the past two decades, a strong interest has been shown in the application of the aluminum matrix composites in the design of many engineering and non-engineering components. Potential uses of these materials are numerous in industries and they include such areas of application as aerospace (satellite struts), defense (electronic instrument racks), automotive (drive shafts and brake disks), sports goods (golf clubs and mountain bicycle frames), and marine (yacht fittings). Aluminum and its alloys with low density and high strength to weight ratio is an excellent candidature matrix material for compositing. Aluminum alloys can be divided into two categories: heat treatable and non-heat treatable alloys. Among aluminum alloys, 2618 (AA2618) is one of the most attractive matrix materials. 2618 aluminum alloy is a heat treatable Al-Cu-Mg-Fe-Ni forging alloy developed for high temperature applications, especially in the manufacture of aircraft engine components. This alloy has good elevated temperature strength up to 204 °C. The addition of small amounts of Fe and Ni produces microstructural stability under thermal exposure. It is anticipated that reinforcing 2618 aluminum alloy with SiC particles can lead to significant improvement in stiffness and strength, both at room and elevated temperatures besides improvement in wear resistance. In this study, structure and mechanical properties of squeeze cast 50 % SiC particle-reinforced 2618 aluminum matrix composites were investigated. 1 wt % Mg to enhance interfacial bonding between Al and SiC was added to commercially available 2618 Al alloy utilized as the matrix alloy. Composites were tested in as-cast and T6 temper states. The examined composite was fabricated by squeeze casting technique. During squeeze casting, the molten Al was poured into the pre-heated mold immediately after transferring the pre-heated SiCp?s. Subsequently, a high pressure of 600 MPa was applied on the mixture by a hydraulic press. Abrasive grade green SiCp?s having the mean size of 30 µm were used as the reinforcement. Structural characterization was carried out after grinding and polishing the samples by utilizing a light optical microscope (LOM), a scanning electron microscope (SEM) equipment with energy dispersive spectroscopy (EDS) and a X ray diffractometer. Room temperature mechanical properties of the composites were determined by hardness measurements and charpy impact tests. The hardness measurements were carried on a hardness tester under a load of 2 kg with a diamond Vickers indenter. Impact tests were conducted on a pendulum charpy-type impact tester on un-notched specimens having width and thickness of 5x5 mm. The results of impact tests were evaluated by averaging the results of three specimens. Wear performance of the composites was determined on a reciprocating wear tester designed according to ASTM G 133 standard. A 10 mm diameter Al2O3 ball was rubbed against the unlubricated surfaces at normal atmospheric conditions (room temperature and 50 % humidity). The stroke of the Al2O3 ball was 12 mm and test loads ranging from 1.5 to 6.0 N were applied for the total sliding distance of 120 m. Wear tests were carried out at two different sliding velocities (0.02 m/s and 0.09 m/s). During wear testing, frictional force data were continuously recorded. After wear test, the wear tracks formed on the composites were examined by a profilometry and a light optical microscope. Microstructural examination revealed presence of dense and pore free microstructure with a homogeneous distribution of SiC particles surrounded by matrix alloy. During microscopic examinations, only Al and SiC peaks were evident on the XRD patterns obtained from 2618 aluminum matrix composite in the as cast and aged states. Application of T6 temper to 50 vol.% SiC 2618 aluminum matrix composites increases the hardness (about 5 %) and decreases the impact resistance (about 12 %). Reciprocating wear tests carried out at two different sliding velocities (0.02 m/s and 0.09 m/s) and test loads in between 1.5 and 6.0 N revealed that the following results: the effect of T6 temper on wear resistance is almost negligible at low test loads and high sliding velocity. However, T6 temper improved the wear resistance (about 50%) at high test loads and low sliding velocity, when compared to as-cast state.   Keywords: Aluminum alloy, wear, composite, SiC