Gas-Enhanced Ultrahigh-Shear Mixing: An Application to Molten Aluminum Alloys

A new mixing technology that explores an integration of ultrahigh shearing with gas injection, directly into the mixer shear zone, has been applied to molten aluminum alloys. The refining and homogenizing effects were assessed through microscopic observations of solidified structures. For the set of process parameters applied, the ultrahigh shear alone caused structural refinement, which doubled the sole effect of gas flotation. Combining ultrahigh shear with gas injection magnified the structural refinement, which substantially exceeded the individual effects, caused by gas flotation and ultrahigh shearing. In addition to matrix grain-size reduction by almost two orders of magnitude, the complex intermetallic compounds, being inherently coarse in conventional castings, were also refined. The results confirmed our earlier observations made through transparent media that an interaction of large volume of fine gas bubbles with the liquid, superimposed on ultrahigh shear, leading to intensive cavitation, generated in the cylindrical rotor–stator apparatus, drastically enhanced the treatment outcome.