Microsegregation development of heavily electromagnetically stirred melt of super high strength Al–10Zn–2·5Mg–2·3Cu alloy

Abstract

Low frequency electromagnetic casting applied to high strength aluminium alloys promoted heavy stirring in direct chill melt, which prevented hot cracking of aluminium alloys never manufactured by direct chill. For instance, Al–10Zn–2·7Mg–2·3Cu alloy was able to be produced by low frequency electromagnetic casting because of the fine grain size, which is small enough, such as 50 μm, when cast into 200 mm diameter billet. It is of importance to understand the microscopic solidification behaviour to properly develop alloy design. Therefore, microsegregation in accordance with solidification progress, including the formation of various kinds of intermetallic compounds, was discussed by precise experiment through compositional analysis using microprobe mapping method. Even under a peculiar solidification condition of refined equiaxed crystals, microsegregation development was apparently similar to a columnar dendrite growth in which the initial solute pile-up was attributed to the diffusion in liquid. For heavily electromagnetically stirred billet, microsegregation was governed by back diffusion.