Effect of mechanical stirring on semi-continuous casting of 7075 aluminum alloy

In order to obtain a superior thixotropic property even in a high strength 7075 aluminum alloy, a billet with a non-dendritic fine-globular structure has been tried to produce by combining a simple mechanical stirring with the vertical semi-continuous casting process. The trials were carried out under the various stirring conditions; the position of a stirring rotor from the bottom of a mold, the shape of a rotor, the volume of a stirring chamber and the stirring rate. When the temperature within the stirring chamber was nearly constant just below the liquidus temperature and dropped drastically near the liquid-solid interface at the certain stirring conditions, a long sound billet with relatively good surface condition could be produced up to the limitation of the descending capacity of the casting machine. The billet had not only a uniformly fine-grained structure of the average grain size of about 30 μm, but also little macroscopic segregation of the solute elements along the radius in the transverse sections at the various positions along the longitudinal direction of the billet.