On the Prediction of Grain Refinement Mechanism in Direct Chill Casting of Aluminum and Its Alloys Under Low Degree Mechanical Forced Convection

The present investigation focuses on grain refinement in pure aluminum and its alloy under mechanical stirring with a very low degree of forced convection of 800 rpm as compared to reported values of up to 8000 rpm during direct chill casting process (DC). Commercially pure aluminum (99.7%) and Al6082 alloy billets were fabricated in an in-house designed DC casting simulator. Mechanical forced convection (MFC) was applied to the melt during casting by a common four-bladed impeller. The microstructural properties of the as-cast billets have been analysed to study the effect of MFC during casting and solidification. The structure of both Al and its alloy is found to be refined in presence of MFC as compared to conventional DC. A combination of simulation, experimental and theoretical approaches has been used to determine the effect of MFC in melt-temperature distribution to propose the mechanism of grain refinement. It has been observed that MFC prominently reduces the temperature gradient and extends undercooling time, resulting in fine grain structure.