**1. Introduction**

Metallic glasses present excellent mechanical and chemical properties that are distinctive among solid metals, and are becoming a research hotspot for current studies in the field of metallic materials [1]. In the field of biological health, biomaterials are developing rapidly and improving people's life quality. Among biomaterials, bioinert metals have been found to be mainly used in cardiovascular scaffolds, orthopedics and dental implants [2–4]. However, the characteristics of these crystalline alloys, instance of high elastic modulus, relative low abrasion resistance, and stress corrosion cracking lead to bone stress shielding. Compared with traditional crystalline metals, metallic glass has an amorphous structure, higher strength, lower Young's modulus, better wear resistance, higher corrosion resistance, and anti-fatigue performance for some Ti-, Zr-, Fe-base systems [5,6]. Over the course of the decades, many metallic glassy alloys have been developed using a wide range of components, including Pd-, Pt-, Zr-, Mg-, Ti-, Co-, and Au-base systems. Among the various di fferent compositions of metallic glasses, Mg-based metallic glass has been widely studied for biomedical applications.

Many amorphization techniques have been developed for metallic glasses, including gun and splat quenching [7], melt spinning [8], high-pressure die casting [9,10], copper mold casting [11], and twin roll casting (TRC). TRC has the advantages of a shorter production cycle, low production cost and lower capital investment compared with conventional techniques [12]. In 1970, following Duvez's seminal discoveries, Chen and Miller developed a TRC technique for producing metastable uniform sheets [13]. Until now, the technique for producing metallic glass strips has been almost solely confined to laboratory-scale research [14–20].

Previous studies have shown that TRC is a useful technique for preparing amorphous alloy sheets with an extensive cooling speed. However, the major research until now has been based on horizontal double roll casters. It is turns out that the heat transfer e fficiency of vertical-type twin roll casting (VTRC) is higher than that of horizontal double roll casting (HTRC), and the cooling speed of VTRC is higher [21,22]. The rapid cooling speed of the alloy during the TRC process is beneficial for reducing segregation, achieving higher uniformity and expanded solid solubility, refining the microstructure characteristics [23]. It enables better utilization to be made of a variety of transition elements that have limited solid solubilities in magnesium alloy, to improve mechanical and chemical properties [24]. As mentioned above, heat transfer VTRC is more e ffective method for continuous production of magnesium alloy sheet than HTRC, and the VTRC process enables achieve a wide range of variable casting speed [25], as a result, the processability and application performance of the products are improved.

However, studies of the rapid casting speed of Mg alloy sheets produced by rapid solidification technology using TRC are rare. In this study, based on the VTRC process, the Mg-RE (RE—rare-earth elements) sheets were produced on a vertical twin roll caster and then were annealed. The microstructure of the Mg-RE sheets was investigated. The corrosion behavior properties were studied. Through this study, we expect to the Mg-RE sheet with a special organizational structure to be potential biodegradable material. Meanwhile, it was implanted into the femur of rat to explore its prospect as biological transplantation material.
