| Preheating processes before the extrusion of rapidly solidified Al-7.9wt%Zn-2.4wt% Mg-1.5wt%Co-0.92wt%Ni alloy powders were studied. Cellular dendrite structures of aluminum alloy powders are found to be decomposed when cold compacted powders are preheated at the temperatures above 490℃. In an aluminum alloy preheated at 490℃ and hot extruded, the density of pores is lower than 0.1% and the maximum diameter of pores is less than 1㎛. The grain size of the aluminum alloy is less than 1㎛ and fine oxide particles are dispersed uniformly within grains and at grain boundaries. After solution (490㎛/1hr) and aging (120㎛/1hr) treatments, the room temperature yield, strength tensile strength and elongation of the aluminum alloy are 71.9㎏/㎟, 76㎏/㎟ and 5.0%, respectively. |
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