Measurement of Air Entrainment During Pouring of an Aluminum Alloy

Understanding and reducing air entrainment in liquid metals is important for improving casting filling systems and liquid metal transfer processes. Air entrainment generates oxide inclusions that reduce the mechanical performance of metals. This paper presents air entrainment measurements for a jet of liquid aluminum alloy A356 plunging into a pool. Measurements are performed in argon and air atmospheres and for a range of jet fall heights. The volume ratio of entrained gas to liquid aluminum poured is measured to be equal to 0.43 for an average jet impact velocity of about 3.8 m/s in the argon atmosphere. This ratio is of a similar magnitude as for water under the same jet parameters. For the corresponding experiment in air, the measured volumetric ratio is only 0.16. It is found that nearly 50 pct of the volume of oxygen entrained is consumed by oxidation, but this alone does not account for the difference between the measurements in inert and oxidizing atmospheres. Instead, the ratio for air is so low because during some portion of the experiment no air was entrained. The onset velocity for gas entrainment for a plunging jet of liquid A356 is found to be 3.9 m/s in an air atmosphere and 3.4 m/s in argon, with the difference attributed to the stabilizing effect of the oxide film on the jet surface in air. These are about three times greater than the onset velocity previously measured for water.