Growth of primary particles during secondary cooling of a rheocast alloy

Abstract

This study is focused on the influences of secondary cooling rate (SCR) and solid fraction upon size of primary solid particles in Al–7.1 wt%Si slurries produced by semisolid rheocasting (SSR) process. SSR slurries with various solid fractions were poured into a wedge-shaped steel die to produce a range of SCRs. The extent of primary particle growth during secondary cooling at various cooling rates was estimated at these solid fractions using a 1/3-power law relationship. The results indicated that, at any given solid fraction, an increase in the SCR caused a smaller growth of primary particles during quench. Furthermore, for any given SCR, primary particles in low solid fraction SSR slurries grew more significantly during secondary cooling than those in high solid fraction slurries. These results were explained based on the effects of SCR and solid fraction on the overlap of solute boundary layers of the adjacent particles and the time available for the growth of the primary particles during secondary cooling stage.