Properties of near- and sub-micrometre Al matrix composites strengthened with nano-scale in-situ Al2O3 aimed for low temperature applications

Mechanical and electrical properties of in-situ Al-Al2O3 metal matrix composites (MMCs) fabricated by powder metallurgy approach using different aluminium powders of particle size 0.8-21 µm and purity 99.8-99.996% were examined. Hot working powder consolidation by vacuum hot pressing at 270 °C and direct extrusion at 425 °C and reduction ratio of 7:1 were applied. Subsequently, extruded composite rods with the diameter of 7.5 mm were cold worked by groove rolling and rotary swaging to the wires with the diameter of 1.1 mm. Detailed microstructural characterization of composite materials was carried out. Stress-strain characteristics of composite wires were measured at 77 and 300 K. In addition, resistivity of all wires were measured by four-probe method between 25 and 300 K and eddy current losses at frequency 72 Hz and temperatures between 18 and 77 K. Obtained results clearly showed that properly designed Al-Al2O3 MMC materials can be utilized at low temperatures e.g., for the thermal stabilization of superconducting wires.