Refining and Recycling of Metal Scraps by Semisolid Processing

In this study, the authors propose a new refining process different from the rheorefining (a screen method) or the melt zone method. This new refining process is based on the gradient of solidification speed of the molten metal poured into a container. The molten metal in the cylindrical container firstly solidifies to columnar crystals from the wall of the container and a liquid phase gradually changes to semisolid state and progresses to the central portion of the container. After an intended semisolid state is achieved, a backward extrusion is carried out to extract the liquid phase component. The liquid component is known to contain a lot of impurity substances. For the refining trials, three aluminium alloys were selected: wrought aluminium alloy A2011, cast aluminium alloy AC4C and aluminium beverage can scraps. Backward extrusion (extraction) was applied twice, and the amount of pure Al increased from 90.59 % in the initial ingot to 96.34 % in the refined material. This new refining process can easily achieve the purification level of that obtained by the rheorefining or the melt zone method.