Dendrite Growth of Continuous Alumina Fiber Reinforced Al-Cu Alloy Composites

Directional solidification experiments have been carried out in continuous alumina fiber reinforced Al-4.5 and 15 mass%Cu alloy composites, to characterize dendrite tip undercooling and inter-dendrite spacing as functions of the copper content and the volume fraction of fiber. The position of the primary dendrite tip in the composite region is located 450∼750 μm below that in the bulk region. The dendrite tip temperature in the composite region is estimated to be 1.2 to 1.7 K lower than that in the bulk region, since the temperature gradient is 2.5 K/mm in the present work. The copper concentration (CS∗) at the dendrite tips in the composite region is higher by 0.05 to 0.15 mass% than that in the bulk region, and increases as the dendrite tip temperature becomes lower. The smaller the fiber interstice is, the higher the CS∗ value. Furthermore, the primary dendrite arm spacing is smaller in the composite region. A model based on the continuity for liquid phase among fibers reveals how the fibers influence the copper concentration of the dendrite tip and the size of the lateral solute diffusion field.