Competitive growth of grains in ZA alloys during continuous casting with heated mould

Abstract

Nucleation and competitive growth of grains in Zn–Al alloys were studied during pulling of ingots under conditions of continuous casting by the Ohno Continuous Casting (OCC) process. Microstructural observation shows that nuclei appearing on the end of the dummy bar have a disordered orientation. However, during competitive growth under conditions of directional heat flow, the ingot grows continuously, and the crystals with less favourable orientations are gradually eliminated. The properties of the alloy greatly influence the selection process. Alloys with a narrow solidification range (ZA5 and ZA8) can directly initiate their columnar structure from nuclei on the end of the dummy bar through competitive growth. Alloys with higher aluminium content (ZA12, ZA22 and ZA27) have a wider solidification range, and their parallel columnar structure evolves only later from the equiaxed crystals on the end of the dummy bar.