بررسي اثر افزودن ذرات نانورس بر ريزساختار، سطح شكست و خواص مكانيكي آلياژ آلومينيوم پيستون در موتور خودرو

INVESTIGATION OF NANO-CLAY PARTICLES ADDITION ON MICROSTRUCTURE, FRACTURE SURFACE, an‎d MECHANICAL PROPERTIES OF PISTON ALUMINUM ALLOY IN AUTOMOTIVE

در اين پژوهش اثر افزودن ذرات نانورس بر ريزساختار، سطح شكست و خواص مكانيكي آلياژ آلومينيوم پيستون در موتور خودرو بررسي شده است. براي اين منظور، نمونه هاي آلومينيومي با/بدون ذرات نانو، به ترتيب ريخته گري گردابي و ثقلي شدند. با بررسي ريزساختاري مشخص شد كه اندازه ي ذرات سيليسيم در نتيجه ي افزودن ذرات نانورس، بزرگ تر و اندازه ذرات در فاز بين فلزي، كوچك تر شده است. نتايج آزمون كشش نشان داد كه در نتيجه افزودن ذرات نانورس، تنش تسليم، تنش كشش نهايي و تغيير طول آلياژ پايه، افزايش و مدول يانگ، كاهش يافته است. با بررسي سطح شكست، مشخص شد كه تقويت آلياژ پايه با ذرات نانورس، منجر به افزايش تعداد ترك ها و كاهش طول آن ها شده است. تحليل شيميايي سطح شكست نيز نشان داد كه آغاز و رشد ميكروترك ها، در نواحي شامل ذرات بين فلزي صورت گرفته و افزودن نانوذرات، تاثيري در محل آغاز و رشد ميكروترك ها نداشته است.

This research investigates the effect of the addition of nano-clay particles on the microstructure, fracture surface, and mechanical properties of the piston aluminum alloy in the automotive engine. To this end, aluminum samples with and without nano-particles were cast in stir and gravity conditions, respectively. Then, these initial cylinders were machined to have standard samples for tensile testing. Uniaxial tensile experiments were carried out in the displacement-controlled condition at a displacement rate of 1 mm/min for both reinforced and unreinforced aluminum specimens. Microstructure observations by the optical microscopy showed that the size of silicon particles increased and the size of intermetallic phases decreased due to the addition of nano-clay particles into the aluminum matrix. In addition, according to the uniaxial tensile test, the yield stress, the ultimate tensile stress, and the elongation of samples, made of the base metal, were enhanced. However, the Young modulus of specimens of the base metal decreased due to the addition of nano-clay particles. The fracture surface by the field emission scanning electron microscopy indicated that the reinforcement of the base material by nano-clay particles increased the number of cracks and decreased the total length of cracks. The mapping analysis by the Energy-dispersive X-ray spectroscopy, which was obtained from the fracture surface of the samples, implied that the crack initiation and the propagation occurred at the area, where intermetallic phases were located. Then, the addition of nano-particles into the aluminum matrix had no significant effect on the initiation location and the propagation of micro-cracks. Further investigations into this topic were done on high-cycle and low-cycle fatigue properties of both reinforced and unreinforced aluminum samples to find the effect of the addition of nano-particles to the aluminum matrix, which will be appeared in futures. Finally, it should be noted that the overall objective was to improve the aluminum alloy with nano-particles to have higher mechanical and fatigue properties in order to be used in high-performance engines.