Annealing Behavior and Tensile Properties of Elevated-Temperature PM Aluminum Alloys

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Abstract
Two rapidly solidified powder metallurgy (PM) aluminum alloys, Al-7.4Fe-3.4Ce and Al-5.7Fe-6.1Ni, were investigated to characterize the annealing response and to relate room-temperature tensile properties with the forging reduction (up to 65%), starting from vacuum-hot-pressed material. The Al-Fe-Ce alloy is typified by a planar/dendritic microstructure having ultrafine (<200-Å) unidentified intermetallic compounds; the Al-Fe-Ni alloy exhibits a planar/coupled-eutectic/eutectic microstructure. At temperatures up to 350°C (660°F), both alloys show excellent stability, which degrades rapidly at higher temperatures. At temperatures above 350°C (660°F), the metastable dispersoids in Al-Fe-Ce transform into acicular (Al3Fe type) and spherical (Al10Fe2Ce type) compounds that grow rapidly with increasing temperature. The eutectic compounds (FeNiAl9) of Al-Fe-Ni are spheroidized before coarsening at temperatures above 350°C (660°F). The strength and elongation of both alloys are enhanced to a maximum value by increased forging reduction; however, they approach the maximum at different rates. Al-Fe-Ce attains maximum strength after 48% reduction, but the elongation continues to increase with additional reduction. In contrast, Al-Fe-Ni does not achieve maximum strength even after 65% forging, and the elongation is far below the maximum value and much lower than that of Al-Fe-Ce. These trends are explained in terms of powder particle bonding (for both alloys) and the breakup of eutectic intermetallics (for Al-Fe-Ni). The poorer properties of Al-Fe-Ni are attributed to incomplete eutectic breakup, even after 65% forging.

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