Microstructure and Thermal Properties of Squeeze Cast Aluminum Alloy Composite Reinforced with Short Potassium Titanate Fiber

Abstract

Aluminum alloy composites reinforced with the short potassium titanate fibers were fabricated to obtain a material having a low thermal expansion rate and good machinability. The composites were fabricated by the squeeze casting. The microstructure, thermal conductivity and thermal expansion behavior of the composites were investigated. Optical microscopy revealed that the fibers were homogeneously distributed in the alloy. However, the fibers were somewhat in a random planar arrangement parallel to the pressed plane when the fiber volume fraction was high. This is due to the forming of the preform by pressing the top and bottom of it. The composites were easily machined using both super alloy and diamond cutting tools. The thermal conductivity of the composite decreased as the fiber volume fraction increased. At the higher volume fraction, the thermal conductivity of the composite in the direction parallel to the pressed plane was higher than that in the transverse direction due to the random planar arrangement of the fibers. The thermal conductivity can be roughly estimated by Landauer’s model. The average thermal expansion coefficient of the composite decreased as the fiber volume fraction increased. The difference in the thermal expansion coefficient between the parallel and transverse directions to the pressed plane was slight, and the experimental values were in good agreement with the theoretical values calculated using the rule of mixture.