The fabrication of particulate composite by in situ oxidation process

A new technique for making particulate composites has been investigated. Unstable oxides such as CuO, SnO2 ZnO and Cr2O3 whose absolute value of standard free energy of formation is smaller than that of Al2O3 were added to moleton aluminum and Al-3.0%Mg alloy. Al2O3 particles are formed in Al-Cu matrix by adding CuO to moleton aluminum at 1273K. Furthermore, by adding CuO the moleton Al-3.0%Mg alloy, MgAl2O4 (spinel) particles are formed. No particles are found in the pure aluminum matrix by adding either SnO2 Or ZnO because of the poor wettability between these oxides and moleton aluminum. However, in case of Al-3.0%Mg alloy matrix, MgAl2O3 particles are formed by adding these oxides because the wettability is improved by presence of magnesium. On the other hand, by addition of Cr2O3, whose absolute value offree energy of formation is relatively large and close to that of Al2O3, in situ particles are formed in neither pure aluminum nor Al-3.0%Mg alloy matrix. The size and shape of particles formed by the in situ reaction depend on temperature of molten metal. The size of in situ particles increases and the shape becomes complicatedly with increase in the temperature of reaction. Although oxide particles formed in this experiment are small and some of them are under 1μm in diameter, macroscopic distribution is not uniform.