Dendrite growth directions in aluminum-zinc alloys

Growth directions in directionally solidified Al–Zn and Zn–Al alloys near eutectic composition

“…As a result, the EBSD signal is very poor but a few points could nevertheless be indexed. As shown in Figure 1E, Al dendrites of the hypoeutectic alloy grow along h1 1 0i (grey point at the bottom), as already found for Al-90 wt.% Zn [1]. This result is confirmed by the metallographic observations shown in this figure: although side arms are not in this plane of the micrograph, as shown by their fragmented aspect, they make an angle of about 60°with the trunk.…”

“…While the thermal gradient was about the same (about 40 C cm À1 ), the pulling speed was reduced by a factor 10 as compared with that used in Ref. [1] (i.e. 6:7 lm s À1 was selected in the present case).…”

“…During solidification of hypoeutectic alloys, fcc dendrites form despite large amounts of zinc in solid solution at high temperature, while hcp ones normally grow for hypereutectic compositions. However, an interesting phenomenon has been reported recently [1] concerning the growth direction of fcc dendrites: while h100i dendrites are normally expected to grow in cubic metals [2], a continuous transition from h1 0 0i to h1 1 0i has been observed as the concentration of zinc c Zn increases from 5 to 90 wt.%. This evolution, called dendrite orientation transition (DOT), occurred between 25 and 60 wt.%.…”

“…This change of dendrite orientation in fcc Al-Zn was interpreted as a modification of the solid-liquid interfacial energy of aluminum c s' ðc Zn Þ as c Zn increases [1,3]. Indeed, dendrite growth directions are dictated by the anisotropy of c s' ; more precisely they are given by minima of the so-called interface stiffness S s' .…”

“…They were then inserted into alumina crucibles for directional solidification in the same Bridgman furnace used in Ref. [1]. While the thermal gradient was about the same (about 40 C cm À1 ), the pulling speed was reduced by a factor 10 as compared with that used in Ref.…”