Distribution uniformity of added elements in twin-roll cast Al–Zn–Mg–Cu alloy by multi-electromagnetic fields

The micromorphology and the concentration of massive precipitates produced by twin-roll casting (TRC) processes without and with multi-electromagnetic fields for Al–Zn–Mg–Cu alloy at 670 °C were investigated in detail by means of optical microscopy (OM) and electron probe micro analyzer (EPMA). The results clearly show that under a 0.2 T static magnetic field, the macro-segregation bands are remarkably alleviated according to the order of uniform static magnetic field, half-wave oscillating electromagnetic field as well as alternating oscillating electromagnetic field, as compared with the non-field TRC process (B = 0). Moreover, under the alternating oscillating electromagnetic TRC process, almost all segregation bands disappear. Additionally, through the observation on a smaller scale, the netlike precipitates elongated and broken by electromagnetic force, and replaced by numerous bulk depositions. EPMA analysis shows that the added atoms are diffused from deposition to α (Al) matrix, resulting in that the solute concentration in and around the precipitates is tending toward uniformity and stability.