Study On Microstructure And Mechanical Properties Of Low Volume Fraction Sub-Micron Al₂O_3p/Al Composites

The Al₂O₃ particle and aluminum powder were mixed uniformly to make preform by high-energy-milling, then the 15%Vol.% Al₂O_3p/Al composites were fabricated by pressure infiltration technigue. The structure and mechanical properties of the composites was improved by adjusting to the alloy elements in matrix, hot extrusion technigue and heat-treatment technique. The microstructure of Al₂O_3p/Al composites was studied by an optical microscopy, scanning electronic microscopy (SEM) and transmission electron microscopy (TEM). The relation of the microstructure and mechanical properties of the composites was studied.We found that speed of ball milling and ball milling time could affect the uniformity of mixture distinctly, and the best ball milling parament is 250 (r·min-1)/2h→350 (r·min-1)/1h. During hot extrusion, the temperature has obvious effect on surface quality of the composites.Microstructure observations show that the composites became denser and the uniformity of reinforcement has been improved both in macro and micro scale after hot extrusion. There areγ-Al₂O₃ particles on the surface of aluminum powder when the magnesium content is low. By increasing the magnesium content, the oxidation film is broken, but the interface reactant increase, and the aging precipitation reduce. After hot extrusion, the dislocation density is high in the matrix, and the grain is refined.The strength and plasticity of the composites is low before hot extrusion, especially, the plasticity is very low. By adjusting the alloy elements in matrix, the strength of the composites has been improved but the plasticity is still low. After hot extrusion, the strength and plasticity of the composites has both been improved. The elongation of 15%Al₂O_3p/Al composite containing 2 wt.% Mg reached 1.58%, which has been improved 10.3 times. The tensile strength of the 15%Al₂O_3p/Al composite containing 4 wt.% Mg reached 473.3MPa. SEM observations show that the composites fractured brittlely in macroscale but the matrix aluminum failed in a ductile manner and there is a great amount of fine dimples and tearing edges after hot extrusion. The results show that the strength and plasticity of the composites is not continuously improved by increasing the magnesium content. Considering synthetically the strength and plasticity, when the magnesium content is 1wt.%, the mechanical properties of the 15%Al₂O₃p/Al composite is the best.