## 1 Introduction  
Wire arc additive manufacturing (WAAM) is widely used in many industries due to its excellent advantages. It reduces the production time and allows net-shape manufacturing. It has also gained attention for its potential applications in the maintenance and repair of structural defects. In WAAM, the localized heat energy is applied to the wire for the deposition, which results in high thermal gradients. Depending on the process conditions, the thermal history of the AM deposition could vary, and it affects the microstructural features, leading to a change in the material properties and structural performance of the AM parts. Many studies have been actively conducted on the aluminum microstructure in the AM process. [PERSON] and coworkers [1] investigated the effects of the deposition speed and current on the morphology of the bead in WAAM of ER-4043 aluminum alloy. He and coworkers [2] performed microscopic analysis on the 4043 Al alloy fabricated by WAAM. They investigated microstructure evolution, tensile strength, and fatigue life cycles of the 4043 Al alloy. [PERSON] et al. [3] examined the microstructure and mechanical properties to investigate the effects of the mean and alternating stresses on the ratcheting behaviors of 4043 Al alloy fabricated by WAAM. [PERSON] and coworkers [4] studied the micropore evolution in the WAAM Al-Cu6.3 and Al-Mg4.5 alloys using X-ray diffraction tomography (XRT). It was found that after interlayer rolling, the number, size, volume, and roundness of micropores in the alloys decreased with an increase in the rolling loads. [PERSON] et al. [5] performed a microstructural analysis on the Al-Mg alloys fabricated by WAAM. They examined the influence of heat input on the microstructure evolution and change in mechanical properties of the Al-Mg alloy. They also reported that the values of microhardness vary with a change in wire-feed speed, while the travel speed does not significantly affect the microhardness. Many studies have also been conducted to understand how the AM parameters affect the microstructural features and mechanical properties for process optimization. [PERSON] al. [6] examined the porosity, temperature distribution, residual stress formation, and hardness of Al-4046 fabricated by WAAM. [PERSON] et al. [7] investigated the microstructure, mechanical properties, and fracture morphology of 5356 Al alloy fabricated by WAAM with a TIG-MIG hybrid heat source. They analyzed the influence of the heat-treated temperature on the microstructure evolution such as the grain growth and phase transformation, which lead to the change in mechanical properties and structural performance. Analyses found that an increase in bypass current in WAAM of 2219 Al alloy increases the size of columnar grains, which leads to the strengthening of Al alloy [8]. [PERSON] et al. [9] studied the effects of the travel speed and welding power on geometric accuracy in the deposition of ER 4043 WAAM. [PERSON] et al. [10] investigated the influence of the scanning speed and welding current on the cold metal transfer (CMT) AM process with a focus on microstructural aspects. [PERSON] et al. [11] studied the relationship among microstructure features, hardness, and residual stress in WAAM of Aluminum alloy 6061 for two deposition patterns: alternate and unidirectional scanning. [PERSON] and coworkers [12] investigated the crack evolution characteristics in Al-Zn-Mg-Cu alloy fabricated by WAAM through a combination of thermomechanical simulations and microstructure analyses. [PERSON] et al. [13] studied the heat treatment methods to improve the microstructure and mechanical properties of AlSi7 Mg0.6 parts fabricated by WAAM-CMT. They proposed the optimal method of heat treatment, which can improve the mechanical properties including the elastic modulus, yield strength, and so on. [PERSON] and coworkers [14] analyzed the WAAM process for AL/steel dissimilar joints to understand how the interpass temperature changes the microstructural features and material properties.