Refining of a DC-casting aluminum alloy structure using surface electromagnetic pulsing

A new technique termed surface electromagnetic pulse refining was developed for improving the solidified structure of a 7A04 aluminum alloy DC-casting. The effect of the pulsed electromagnetic field on the solidified microstructure and properties of the alloy was investigated. From the viewpoint of potential energy, the dynamics of forming nucleus and the grain motion were theoretically predicted based on the concepts of the action of the pulsed electromagnetic energy on the melt or particles. The experimental results indicate that the solidified structures are modified by the electromagnetic pulse from rose-like structures to globular structures with a fine grain size. The grain size in the edge zone and central zone of the billet is decreased by 22.7% and 14.2%, respectively, and the strength and plasticity of the alloy are also increased. The grain refinement can be explained by the nucleation rate increases, because the electromagnetic energy helps to decrease the critical Gibbs free energy of the system. In addition, the electromagnetic pulse appears to increase potential energy of the primary α-Al, which quickly attains a steady state in the melt.