Suppressing freckles during solidification due to periodic motion of top liquid layer

In the past, one main area of focus in the solidification of a liquid binary alloy has been the investigation of strategies for the elimination or minimization of the presence of “double-diffusive convection”, the main cause of poor quality alloys. In particular, “freckles” occurring in the solidification process cooled from the bottom can result in severe material defects in the final product. The objective of this study is to investigate the effect of a periodic lid-driven flow on the development of double-diffusive convection during solidification from below to aid in the removal or reduction of the occurrence of this convection that causes the formation of freckles. A hyper-eutectic aqueous ammonium chloride (NH4Cl–H2O) solution was used as the test sample and was contained in an enclosure cooled from the bottom to study flow development and heat and mass transport phenomena during solidification. Flow visualization using the shadowgraph technique and measurements of the temperature distribution, the concentration distribution, and the movement of the liquid–mush interface were conducted during solidification. The experimental results revealed that the imposed periodic lid-driven flow had a positive effect on the process by suppressing the plumes emanating from the channels and reducing the strength of the double-diffusive convection.