Dendrite growth directions in aluminum-zinc alloys

Abstract

The dendrite growth directions in fcc aluminum-zinc alloys have been measured by electron backscattered diffraction (EBSD) as a function of the zinc concentration,c o . In specimens produced by directional or Bridgman solidification, 〈100〉 dendrites were observed up to 25 wt pct Zn, whereas, above 60 wt pct, the dendrite growth direction was clearly 〈110〉. In between these two concentrations, the angle, φ(c o ), between 〈100〉 and the 〈hk0〉 dendrite growth direction, varied continuously between 0 and 45 deg asc o increased. Following an analysis of growth directions suggested by Karma but restricted to two dimensions in a (001) plane,[1] this angle was fitted with a function ¼ arcos (−η4/4η8), where η4(c o ) cos (4φ) and η8(c o ) cos (8φ) are the first two contributions to the solid-liquid interfacial stiffness anisotropy in a (001) plane. This analysis also gives a qualitative explanation to textured seaweed structures observed aroundc o ≈ 25 and 60 wt pct. These findings are discussed in light of recent measurements of the weak interfacial solid-liquid energy anisotropy of aluminum[2,3] and of dendrite growth directions in hcp Zn-Al alloys.[4]