## 1 Introduction  
AA7075 and AA2024 aluminum alloys are effective, widely used alloys in many modern engineering applications, for example, in the aerospace, transportation, and military sectors, due to their high strength-to-weight ratio [1; 2]. Important applications include the construction of strong stiffeners and vertical stringers from AA7075 on AA2024 sheets in the fabrication of lower fuselage skin panels and flat roof panels in the aerospace industries [3; 4]. The joining of these high-strength alloys via traditional welding techniques is still a challenge. Additive manufacturing technology has recently been applied in a number of engineering disciplines, including printing, electrical circuits, and surface protection for various materials, like metals, ceramics, and polymers, where the costs, material consumption, and time are relatively reduced [5; 6; 7; 8; 9]. This technology has been applied to fabricate complex 3D parts. For metallic materials, it can be classified, based on the component production methods used, into two classes: additive manufacturing-based fusion and additive manufacturing-based friction processes. The first class is carried out in a liquid state based on the principles of a casting process that depends on high heating and cooling rates of the materials used [10]. Technical problems and limitations during the fusion-based techniques [11; 12] of aluminum alloys include the formation of dendrite structure, porosity, and solidification cracks. Moreover, a controlled atmosphere is needed [13; 14]. The second class is based on the principles of friction stir welding and processing [15; 16; 17; 18] and is categorized as a solid-state additive manufacturing technique. The peak temperature of the additive process ranges up to 60-80% of the melting temperature of the fabricated part [19; 20]. Thus, the inherent technical problems and limitations associated with the fusion additive manufacturing process are negligible [21; 22]. Friction-based additive manufacturing techniques have been adopted as a preferable technology to produce metallic components for many industries [23; 24; 25]. These techniques include additive manufacturing processes like additive friction stir welding [10], additive friction stir surfacing (using a hollow shoulder [23; 26; 27], and additive friction stir deposition (AFSD) [28; 29; 30; 31]. Based on the same principles as friction stir welding, AFSD is a solid-state technique [3; 32]. Thus, it can be considered a promising technology for the deposition of a wide range of metallic and composite materials. The AFSD process involves use of a rotating rod set against a fixed substrate plate. In order to construct continuous multilayer bulk materials, the contact end of the rotating rod is plasticized and deposited on the substrate as a result of the frictional heat generated at the interface surface between the rod and the substrate [33; 34]. The quality of the deposited materials using the AFSD process depends on the process parameters, including the consumable rod rotation speed, the feeding rate, the downward axial force [35], the initial materials (substrate and rod materials), and the rod diameter [28; 29; 36]. These process parameters directly influence the heat generated and play a significant role in the deposited material's adhesion with the substrate and the metallurgical properties of the deposited materials. AFSD of different aluminum alloys has attracted the attention of many researchers in recent years [37; 38]. [PERSON] et al. [29] utilized AFSD to modify the dendritic grain structure of as-cast A356 aluminum alloy rods (20 mm diameter) by building several layers at different deposition rates with a constant CRRS of 1200 rpm. They reported that the as-cast material was deposited in continuous layers without interfacial defects between the deposited layers and the substrate alloy. Moreover, the produced deposited parts showed a high degree of grain refining and higher hardness compared to the as-cast A356.