Numerical simulation of Zn coating solidification

Abstract

A. SÉ MOROZ, L. STREZOV, and M. RAPPAZ A numerical model, which simulates nucleation and growth of Zn grains, has been developed in order to describe quantitatively the solidification of Zn coatings during the hot-dipping process. The inputs of the model are the nucleation distribution, which has been measured by electron backscattered diffraction (EBSD), and the dendritic growth kinetics, calculated with an analytical model of a parabolic dendrite tip modified to account for the interactions with the coating interfaces. The model predicts the shapes of the grain envelopes as a function of the grain orientation and the texture induced by growth. Three types of grain envelopes have been evidenced, depending on the angle between the c-axis and the normal to the coating plane. Moreover, it has been shown that growth reinforces the already existing {00.1} nucleation texture, in good agreement with experimental data. The model also predicts the cooling curve, including recalescence, and the grain size. Thus, it is used to describe the effects of Pb additions on solidification. In particular, it has been shown that Pb increases the nucleation undercooling and strongly decreases the density of active nuclei, thus resulting in a much larger grain size. A. SÉ MOROZ, formerly Ph.D Student, Institute of Materials, Ecole Polytation. The following grain envelopes can be distinguished. technique Fédérale de Lausanne, is Scientist, Alstom, Brown Strasse, 5400 Baden, Switzerland. L. STREZOV, Leader, is with the Pyrometallurgy Group, BHP Billiton, Minerals Technology, Newcastle Technology Centre, Wallsend, (1) The hexagonal shape corresponds to grains that have NSW2287, Australia. M. RAPPAZ, Professor, is with the Institute of Materitheir basal plane parallel to the coating plane. Their six als, Faculty of Engineering, Ecole Polytechnique Fédérale de Lausanne, primary dendrite arms grow along the ͗10.0͘ directions,

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

“…More importantly, the dendrite growth direction in both specimens correspond to h1 0 1 0i as indicated by the point near the label X 0 in the pole figure. This growth direction is identical to that measured by Sémoroz et al [11] in zinc alloys with various aluminum concentrations and by Quiroga et al [13] in Zn-0.2 wt.%Al. This seems to confirm that aluminum does not change the regular h1 0 1 0i growth direction of Zn dendrites in the basal plane.…”

“…On the other hand, it is much higher in hcp zinc (about 30% between the c-direction and the basal plane) [7] and causes dendrites to grow primarily along the h1 0 1 0i directions. h0 0 0 1i dendrites can also grow in Zn-Al, but with a velocity about half that of h1 0 1 0i dendrites [11]. Since zinc influences the growth of aluminum dendrites, the question that is addressed in the present report is the following: is it possible to influence the growth directions of zinc dendrites by aluminum solute elements and make them grow along h1 1 2 0i, i.e.…”

“…6:7 lm s À1 was selected in the present case). Indeed, as pointed out by Sémoroz et al [11], too large a velocity in the hypereutectic alloys induces the formation of equiaxed grains, unless poisoning solute elements such as Pb, Bi or Sb are added.…”

Connectivity of Phases and Growth Mechanisms in Peritectic Alloys Solidified at Low Speed: an X-Ray Tomography Study of Cu-Sn

“…The color index measures the angle a between the c-axis and the normal n sf to the sheet: as can be seen, there is a very large proportion of basal grains (blue and green grains)-in fact much larger than that expected for a random distribution of the c-axis. This is evidenced in the statistics of the angle a shown in Figure 5b, in which two distributions of nuclei orientations (random and basal) have been set so as to match best the experiments [14,20,21]. Not only is the proportion of basal grains larger in such coatings, but their surface fraction (i.e.…”

“…Heterogeneous nucleation and growth of anisotropic Zn is responsible for some of the textures seen in hot dip galvanized coatings on steel sheets [14,20,21]. In this process, a clean pre-heated steel sheet is immersed in a Zn-0.2 wt.% Al bath.…”