**1. Introduction**

Magnesium (Mg) alloys have high specific strength and ductility resulting in their use in various applications from automobile, aerospace, and orthopedic applications. However, its low cold workability near room temperature due to its hexagonal packed crystal structure limits its use [1–3]. Magnesium alloys have been classified by many researchers as a super lightweight structural metal, attracting a lot of attention in the automobile and aerospace industries where production of light, super-fast machines requiring less fuel consumption through weight reduction is of high priority [4,5]. Magnesium–Lithium (Mg–Li) alloys are gaining more and more interest in scientific research studies as well as in industrial applications owing to their super lightweight, high specific strength and good formability making it one of the most ideal structural materials for 3C intelligent electronics, medical devices etc. [6–8].

Many researchers have employed the use of alloying and various mechanical procedures to enhance the mechanical property of Mg-Li base alloys [9,10]. Notable amongst them is the ECAP (equal channel angular pressing) process for achieving ultrafine grains (UFG) by severe plastic deformation (SPD) [11,12]. ECAP has advantages of producing large bulk materials for various industrial applications, with improvement in strength and ductility properties [13–15]. Conventional ECAP process however has typical drawbacks of reinserting billets into the die for every pass, resulting in inconsistencies in temperature applied for each pass [16–18]. Some researchers have therefore resorted to the development of novel processes with higher production efficiency, such as repetitive upsetting (RU) [19–21] and rotary die equal channel angular pressing (RD-ECAP) [22–24]. Also, another effective plastic deformation in use is the rolling technique. Magnesium alloys have a dense hexagonal structure with few slip systems. This makes it easy to induce stresses when rolling at large strain rates which results in very low yield of magnesium alloy sheets [25]. However, the addition of lithium to the magnesium alloy forming Mg–Li alloy results in the formation of a β-rich Li phase which greatly increases the dislocation slip system and improves the plastic deformation ability of the Mg-Li alloys [26]. The results obtained from the reported research [27,28] show that, the use of rolling technique leads to an improvement in the strength properties of the Mg-Li alloy, activate more slip systems, enhance the ability of intergranular co-opening and improve the ability of plastic deformation at room temperature (RT). In the rolling process, strong basal texture will be formed [29]. Research done by the reference [28] employed unidirectional (transverse and longitudinal) and cross (combination of transverse and longitudinal) rolling routes to improve the mechanical properties of Mg-9Li-1Al alloy. The unidirectional rolling routes reached 170 MPa tensile strength whereas the cross rolling route reached 243 MPa respectively. During the rolling process, compression twins may be formed. Therefore, in the rolling process, the original structure can be refined by pretreatment and the morphology and texture of the material can be controlled during the rolling process. Different researchers [30,31] have employed the use of ECAP with further rolling, applying it in a wide variety of alloys and have achieved sufficiently good tensile strength and ductility.

This research therefore seeks to investigate the effect of employing a combination of RD-ECAP with further room-temperature rolling techniques on the microstructural evolution and mechanical property changes of Mg-9Li duplex alloy.
