2015 Volume 56 Issue 1 Pages 160-166
To develop a machinable aluminum alloy composite with high strength, high rigidity and low thermal expansion rate, potassium hexatitanate short fibers were selected as the reinforcements for the composite. JIS-AC8A alloy was used as the matrix metal, and two kinds of potassium hexatitanate short fibers were used as the reinforcements. The composites were fabricated by squeeze casting. The microstructure, thermal conductivity, thermal expansion behavior, and mechanical properties under compressive stress of the composites were investigated. These properties of the composites were compared with those of the unreinforced AC8A alloy and the composites reinforced with various reinforcements such as potassium titanate whisker and aluminum borate whisker. Optical microscopy revealed that the reinforcements were three-dimensionally arranged in the alloy matrix, and no agglomeration of the reinforcements or porosity was observed, indicating that the melt infiltration into the reinforcement preform was perfectly accomplished. The thermal conductivity of the composite decreased as the reinforcement volume fraction increased, and the value of the short fiber-reinforced composite is similar to that of the potassium titanate whisker-reinforced composites. This tendency can be roughly estimated by Landauer’s model. The average thermal expansion coefficient of the composite decreased as the volume fraction increased, and the experimental values were in good agreement with the theoretical values calculated using the Shi’s model. Although the compressive elastic modulus and 0.2% proof stress increased due to the reinforcement at both room temperature and 523 K, the increase in the volume fraction from 25 vol% to 45 vol% had a small effect on improving these mechanical properties for the short fiber-reinforced composite.