In situ dispersion of yttrium and calcium oxides in mechanically alloyed Al-Y and Al-Ca alloys

With a purpose of attesting preferential oxidation of alloying elements which have low solid solubility in aluminum, Al-5at%Y and Al-5at%Ca alloys were mechanically alloyed with or without addition of metal oxides; CuO and Fe2O3. Yttrium and calcium were chosen as the alloying elements since they have a higher oxidation tendency than Al and low maximum solid solubility. Mechanically alloyed powders were consolidated to the P/M materials by hot-extrusion. The constituent phases, microstructures and mechanical properties were examined for the mechanically alloyed powders, as-extruded and heat-treated P/M materials. It has been shown that the added oxygen, either from the milling agent or from the added oxide powders, acted as the oxygen sources for internal oxidation. Yttrium in Al was shown to be preferentially oxidized to Y2O3 and Al5Y3O12, while calcium in Al to CaO and CaAl4O7. Thus, in-situ dispersion of Y2O3, Al5Y3O12, CaO and CaAl4O7 has been attained by the solid state reactions induced in Al-Y and Al-Ca alloys. The Al-Y based P/M materials with addition of oxide show high tensile strength of above 600MPa at room temperature.