# Mechanical Properties Analysis of WAAM Produced Wall Made from 6063 Alloy Using AC MIG Process
## 1 Introduction
Although the average grain size in pulsed AC mode was slightly higher, it maintained a favorable and uniform microstructure with a balanced distribution of equiaxed and columnar grains, contributing to improved material homogeneity and mechanical performance [13]. Furthermore, image-based symmetry analysis has demonstrated that pulsed AC deposition yields the best bead symmetry, further supporting its suitability for high-quality and consistent WAAM applications [14]. Grain size in WAAM is influenced by the applied power and polarity change frequency, with a higher EN pulse rate promoting a predominant equiaxed structure, reducing columnar growth, improving structural uniformity and increasing deposition weight [15]. Solidification cracks in aluminum alloys during the WAAM process occur within the liquid melt pool and is primarily caused by a wide solidification range, a columnar dendritic grain structure and the inability of the residual liquid to compensate for shrinkage-induced stresses near the solidus temperature [16]. An important prerequisite for the successful use of Al-Mg-Si alloys in WAAM is overcoming their susceptibility to such hot cracking. One of the most effective measures to prevent hot cracking is grain refinement. A promising approach to achieve this is the use of an advanced Al-Mg-Si alloy inoculated with a TiBcontaining structural refiner [17]. As a result, this modified alloy exhibits no macroscopic cracking in the deposited material. The resulting microstructure is characterized by fine, equiaxed grains smaller than 30 \(\upmu\)m. These microstructural features are attributed to preferential heterogeneous nucleation, which reduces the tendency for epitaxial grain growth [18]. Due to its widespread use in structural applications and its favorable response to heat treatment and grain refinement, making it a promising and cost-effective candidate for WAAM technologies, 6063 is selected. To further enhance its processability for additive manufacturing, a TiB\({}_{2}\)-refined Al-Mg-Si (6063) filler wire specifically developed for WAAM was used in this study, providing improved grain refinement, reduced cracking susceptibility and better microstructural control. The high susceptibility of 6000 series aluminum alloys to cracking during solidification poses a challenge for additive manufacturing. However, the use of a TiB-alloyed AlMg0.7 Si welding wire (S Al 6063-TiB) enabled the production of aluminum parts with fine, equiaxed grains and low porosity, effectively avoiding solidification cracks. A key advantage of the 6000 series alloys is their ability to undergo heat treatment, which significantly improves mechanical properties. After heat treatment, both the transverse and longitudinal specimens exhibited yield strength, tensile strength and ductility that matched or exceeded those of AW 6063-T6 in wrought form, demonstrating the alloy's great potential for high performance in WAAM applications [19]. Residual stresses in aluminum components produced by WAAM are primarily caused by uneven heating and cooling during solidification, resulting in forced thermal contraction [20]. These stresses are usually tensile stresses that reduce fatigue strength and potentially lead to deformation if they exceed the yield strength of the material [21; 22]. Residual stress in WAAM components is strongly influenced by clamping conditions, the path planning strategy, welding parameters, the interlayer temperature and the component geometry, whereby longitudinal stresses (stresses in the welding direction) generally predominate along the build-up direction. These stresses are commonly measured using techniques such as neutron diffraction, X-ray diffraction (XRD) and hole-drilling [23]. During WAAM production of aluminum alloys, significant residual tensile stresses can occur, especially near the substrate and along the build direction, that approach the yield strength of the material, highlighting the need for stress reduction strategies such as process modifications or post-processing treatments [24].