Effect of Electromagnetic Field on the Micromorphology of Twin-roll Cast 7075 Alloy

The micromorphology and the grain size of 7075 Al alloys were investigated by optical microscopy (OM). The rolled sheets were fabricated by electromagnetic field. It is found that the dendritic crystal of 7075 alloy sheet by alternating oscillating twin-roll cast (TRC) is severely broken, stretched, refined and equiaxed under the condition of pouring temperature 670 °C, compared with that of traditional TRC sheets. Meanwhile, the microstructures of the rolled sheets by static magnetic field (MF) process are also refined and stretched to some degrees with exciting current of 100 A. Segregation bands in center of TRC sheets are dramatically alleviated under the conditions of DC magnetic field and alternating oscillation field, while the influence of alternating oscillation TRC process is much more powerful. Hardness of 7075 sheets both on transverse and surfaces increases in turn along with traditional, static MF and alternating oscillation TRC. With increasing of electromagnetic intensity, the hardness and the properties of sheets are further improved. No matter wherever in the sheets, the influence of electromagnetic field will be further improved by elevated temperature.