Relieving segregation in twin-roll cast Mg–8Al–2Sn–1Zn alloys via controlled rolling

Abstract Twin-roll casting (TRC) of Mg alloys with high Al content has unique advantages and broad development prospects. However, the severe segregation of high-alloyed Mg caused by TRC technology is difficult to solve at present, which restricts its practical application. In this work, the homogenization of coarse segregated phases in a twin-roll cast Mg–8Al–2Sn–1Zn (ATZ821) alloy was successfully achieved by a method combining solid-solution heat treatment and controlled rolling, which is suitable for industrial-scale production. In addition, the evolution of the microstructure was studied in detail. It was found that phases dynamically precipitated and dissolved repeatedly during the hot rolling process, and the evolution of entire second phases can be classified into three stages, i.e., the net dissolution, balancing and net precipitation stages. During the process, the large-size chain-like eutectic phases evolved into a fine and nearly spherical (∼0.4 µm) morphology that was uniformly dispersed in the Mg-matrix due to the thermodynamic coupling and the Ostwald ripening effect. Moreover, a fine grain microstructure (∼4 µm) was obtained. The formidable segregation problem of twin-roll cast Mg alloys with high Al content was solved, which is an important finding for the industrial application of high-alloyed twin-roll cast sheets.