بررسي تاثير فعال سازي سطح ذرات Al2O3 به روي ريز ساختار نانو كامپوزيت هاي Al-Al2O3

Effect of surface modification of Al2O3 particles on the microstructure of Al-Al2O3 nanocomposites

در اين تحقيق به منظور افزايش قابليت تر شوندگي ذرات Al2O3 در مذاب آلياژ آلومينيوم ،ابتدا سطح ميكرو و نانو ذرات Al2O3 بوسيله روش الكترولس دو مرحله اي با لايه Cu پوشش داده مي شوند. متعاقبا اين پودرها به داخل مذاب آلياژ آلومينيوم A356 تزريق مي شوند و نمونه هاي كامپوزيتي شامل درصدهاي وزني مختلف ذرات Al2O3 (ميكرو و نانو ذرات، پوشش داده شده و پوشش داده نشده) بوسيله روش ريخته گري گردابي توليد مي شوند. آناليز ذرات پوشش داده شده و نمونه هاي ريختگي با استفاده از ميكروسكوپ هاي OM و SEM و TEM انجام گرفته است. نتايج نشان مي دهد كه وقتي ذرات پوشش داده شده با مس استفاده مي شوند به طور قابل توجهي تر شوندگي ذرات Al2O3 در مذاب بهبود مي يابد، به دليل تشكيل اينترمتاليك CuAl2 در فصل مشترك زمينه / تقويت كننده پيوند فصل مشترك قوي تري ايجاد مي شود، جدايش ذرات محدود تر شده و توزيع يكنواختي از ذرات Al2O3 در زمينه مشاهده مي شود.

Aluminum matrix composites containing dispersion of nano-sized Al2O3 particles are under attention for many applications in aerospace and automobile industries because of their light weight, high strength and good wear resistance properties. These kinds of nanocomposites are widely prepared through stir casting method; however in this method wettability of reinforcement particles within the matrix melt is really poor. In this study in order to improve wettability of Al2O3 particles in Al matrix, surface of Al2O3 particles (50nm diameter) were modified with metallic Cu layer (20nm thickness) by using two step electroless coating techniques. Subsequently Cu coated Al2O3 particles were annealed at temperature of 450 °C and then injected into the molten Aluminum. Nanocomposite samples containing different weight percentage of Al2O3 particles were prepared by stir casting. Morphology of Cu coated particles and distribution and interfacial reactions in the cast nanocomposites were characterized using scanning electron microscopy (SEM) equipped with an energy dispersive spectroscopy (EDS) and transmission electron microscopy (TEM). The results show when copper coating particles are applied, reinforcement wetting by molten matrix significantly improves, strong interfacial bonding appeared due to the formation of CuAl2 intermetallics in matrix/reinforcement interface, reinforcement’s segregation limited and uniform distribution of Al2O3 nano particles within Al matrix observed. Density, hardness and compression strength of samples were investigated and it is revealed that the amount of hardness, compressive strength and porosity increased when Cu coated particles used and weight percentage of nano Al2O3 particles increased.