## 1 Introduction  
Magnesium alloys are favorable for the transportation industry owing to their high specific strengths [1]. However, the properties of wrought Mg alloys, like poor formability and mechanical anisotropy, lead to their limited use for lightweight applications [2; 3; 4]. The weight percentage of magnesium used in a typical passenger car has remained approximately 0.5% for two decades due to these factors [5; 6]. Since the widespread deployment of Mg alloys in the automotive industry could lead to significant improvements in vehicle fuel efficiency, Mg alloy formability has been the subject of considerable research interest. Mg alloys have low formability at room temperature [3; 7; 8], although recent experimental work has shown that it is possible to process pure Mg with high formability at room temperature [9]. The reason for this typically low formability was that Mg alloys have a hexagonal close packed (HCP) crystal structure and greatly prefer basal slip when deformed at room temperature [10; 11; 12; 13]. However, in order to accommodate plastic deformation, five different slip systems (in addition to twinning) must be active to meet the [PERSON] criterion [14]. This was a considerable technical obstacle, as prismatic <a>, pyramidal <a>, and pyramidal <a + c> slip all have critical resolved shear stresses that are multiple times higher than basal <a> slip [13]. Numerous strategies exist to circumvent or alleviate this limitation. For example, the addition of Rare Earth (RE) elements to Mg alloys minimizes the critical resolved shear stress (CRSS) to enable additional modes of deformation [15; 16; 17]. Other studies have also shown that refining the grain structure promoted grain boundary sliding and improved formability [17; 18; 19]. Forming at temperatures between 280 \({}^{\circ}\)C and 500 \({}^{\circ}\)C generally improves the alloy's deformation response [11; 20], but is an energy intensive process. Twin-roll casting, for example, was a common method used to fabricate Mg alloy sheets [21]. Other authors have attempted to form Mg alloys using multiple cold rolling and annealing steps, such as [PERSON] et al., who recently achieved refining grain structure and formability in AZ31 through repeated 10-15% cold rolling passes with 30 min intermediate anneals at 250 \({}^{\circ}\)C [16]. The anisotropy generated in Mg and Mg alloy from processing are a result of strong basal textures and grain aspect ratios, typically seen after conventional rolling steps. The basal texture introduces a significant anisotropic effect when it comes to tensile deformation properties. The effect of different tensile loading directions on a rolled Mg plate have been studied in the past, emphasizing the anisotropic effect that strong basal texture has on the yield strength, strain hardening behavior and Extension to Failure (ETF) [22; 23; 24]. Ideally, elimination of textures and large grain aspect ratios are desired for formability of Mg alloys, and methods for grain refinement are still being studied today. In order to circumvent the challenges associated with rolling and twin roll casting, several studies have utilized extrusion techniques that cause severe plastic deformation (SPD) to refine the Mg grain structure [17; 19]. One of these techniques, equal channel angular processing (ECAP), was also capable of rotating the Mg texture away from the basal texture after multiple passes [12; 22]. This process has been able to improve the yield strength, formability, and ETF of Mg alloys [12; 22; 23; 24] and even their hydrogen storage properties [25]. Unfortunately, the batch size and scalability of this and most other SPD methods are currently limited to amounts that would not be feasible for industrial-level production [5]. However, a new form of Friction Stir Back Extrusion (FSBE) called Shear Assisted Processing and Extrusion (ShAPE) has recently shown promise as a method to control Mg alloy grain size and texture [5; 26; 27; 28; 29].