| Ultra-fine, monocrystalline, gas atomized Al 99.7% powder was consolidated into profiles by means of direct extrusion. Conventional approach, with complicated (i.e. expensive) procedure steps of powder degassing and encapsulating, was avoided. Structural stability of compacts and enhanced mechanical properties, predominantly those at elevated temperatures, were of paramount interest. Extrusion yielded sound profiles with ultra-fine grained (UFG) microstructures of fcc-Al matrix reinforced with homogenously redistributed α-alumina dispersions. Nano-scale dispersions, originated from torn surface oxides envelopes, effectively acted as dislocation movement and grain growth barriers. Microstructures were found to be intact to long term high temperature exposures. Relatively high tensile strengths (Rm up to 310 MPa) accompanied with good ductility (A10 ∼ 10%) and impact fracture toughness (KC ∼ 45Jcm-2) were determined at room temperature. Due to unique structural stability no pronounced strength decline was observed and compacts retained their relatively high strength even at testing temperatures of 500 œC (∼ 70 MPa). Simple consolidation route without prior degassing resulted in the structure containing micropores filled with entrapped and compressed gasses. These pores had no negative effect on room temperature mechanical properties, though expansion of entrapped gases may lead to the reduction of high temperature ductility. |
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