HSP (High shear processing) process is a novel technology for conditioning alloy melt prior to solidification processing. Implemented by a rotating screw, the alloy melt is directly subjected to intensive shearing under high shear rate and high intensity of turbulence. Consequently, the sheared alloy melt has uniform temperature, uniform composition and well dispersed oxide or other inclusion particles. In this way, cast products with fine and uniform microstructure, uniform chemical composition and much reduced or eliminated cast defects with high integrity can be produced. More importantly, intensive melt shearing can effectively disperse the oxide particles present in the alloy melt and thus these oxide particles can act as potent nucleating sites to enhance the heterogeneous nucleation process during the solidification, resulting in a significant physical grain refinement. The process has the following advantages (Z. Fan, 2009):
• It is applicable to both cast and wrought alloys without any limitation to alloy composition and without any poisoning effect by alloying elements.
• It turns the usually harmful oxide inclusions into useful nucleation sites for grain refinement;
• It has no detrimental effect on down stream processing;
• It increases the tolerance to the impurity elements (e.g., iron), so more scrap metal can be directly recycled in-house without gong through chemical purification.10,11
• It does not contaminate the alloy and therefore does not cause any concern for further recycling.
Z. Fan, M. X. (2009). Melt conditioning by advanced shear technology (MCAST) for refining solidification microstructures. International Journal of Cast Metals Research, 1-6.