Unidirectional solidification of a Zn-rich Zn–2.17 wt%Cu hypo-peritectic alloy

Abstract

Unidirectional solidification of a Zn-rich Zn-2.17 wt%Cu hypo-peritectic alloy has been carried out to investigate the microstructure evolution over the growth velocity range 0.02–4.82 mm/s ata temperature gradient of 15 K/mm by means of the Bridgman technique. Regular and plate–like two-phase cellular structures were observed in samples grown at growth velocities V above 0.48 and 2.64 mm/s,respectively. The dominant microstructure in samples grown below 0.22 mm/s was dendrites of primary sin a matrix of secondary η. Intercellular spacing ι decreased ε with increasing growth velocity V such that ιV1\\2 is a constant of 316 ± 55 µm3/2/s1/2. Secondary dendrite arm spacing λ2 of primary decreased with increasing V such that λ2V1/3 isa constant of 14.9 ± 0.9 µm4/3/s1/3. The observed transition from regular cells to plate-like cells of η is discussed on the basis of competitive growth and crystallographic effect.