Nano-sized dispersoids formed by solid state reactions in mechanically alloyed aluminum based materials

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Mechanically alloying was carried out for the Al-Fe and Al-Mn systems from three different starting materials : (1) powders from prealloyed ingots, (2) mixed powders of pure elements and (3) pure aluminum powder with addition of oxides of alloying elements. Mechanically alloyed powders were consolidated to the P/M materials by vacuum hot pressing and hot extrusion. Structures and mechanical properties were examined on the P/M materials. It has been shown that oxide addition is an effective way to obtain materials of superior mechanical performance since dispersion of Al_2O_3 and aluminide compounds is obtained in situ by the displacement reaction of oxygen during or after mechanical alloying treatment. Furthermore, mechanically alloyed materials were produced in the Al-Cr, Al-Hf, AL-Mo, Al-Ti, Al-W, Al-Zr systems by adding the oxide of alloying elements to aluminum powder. X-ray diffraction revealed that the added oxides were discomposed and Al_2O_3 and aluminide compounds were formed … More in these materials. These aluminum alloy systems are known to be difficult to prepare by the melting and casting method because of significant differences in the density and melting point between aluminum nd slloying elements. It has been confirmed that mechanical alloying with additon of the oxides of alloying elements is an effective alloying method for such alloy systems. Since formation of dispersoids in these materials occurs by solid state reactions, the amount and average size of dispersoids can be more easily controlled than in the liquid state reactions. Thus, oxide addition enables to obtain nano-sized dispersoids formed by solid state reactions in mechanically alloyed aluminum based materials. Hardness increases were observed in many of these materials with the progress of such solid state reactions when consolidated materials were heated at very high temperatures such as 773 or 873K.The highest hardness increase of HV75 was observed in Al-Mo system when its hot-extruded material was heated at 873K for 40ks. Most of the as-extruded materials of these alloy systems showed high tensile strength above 500MPa, and thus dispersoids formed by solid state displacement ractions of oxygen in mechanically alloyed materials are shown to be effective for strengthening aluminum based materials. Less