## 3 Results
### Hardness Evaluation  
After the heat-treatment process, the hardness of the samples was also assessed. The investigation revealed that fluctuations in hardness primarily depend on the solutionizing temperature. The summarized results are presented in Figure 2, representing the hardness of all samples treated at a specific solutionizing temperature; it provides valuable insights into the microhardness's behavior.  
Previous authors [10; 35] have determined that hardness depends on the presence of alloying elements such as Mg and Si, which form intermetallic phases in the presence of Fe, among other elements, as well as the time and temperature of the aging process. With a solutionizing temperature of 540 \({}^{\circ}\)C for 3 h, followed by artificial aging at a temperature of 170 \({}^{\circ}\)C for 18 h, hardness of up to 98 HV (SD = 2 HV) was achieved. At these solutionizing temperatures, a more significant quantity of alloying elements can be retained as a solid solution, allowing for the precipitation of alloying elements during artificial aging, which forms strengthening phases.  
The hardness of an alloy is primarily attributed to the presence of GP zones and strengthening phases, as reported previously [36; 37; 38; 39]. Notably, at a temperature of 540 \({}^{\circ}\)C, the precipitation of Mg\({}_{2}\)Si phases and GP zones is favored; then, microhardness values of up to 98 HV (SD = 2 HV) were obtained for these samples. In contrast, the lowest microhardness was observed for a solutionizing temperature of 520 \({}^{\circ}\)C.  
The initial microhardness of the as-received sample was measured as 101 HV (SD = 4.5 HV), but it is worth noting that a slightly increased hardness does not necessarily enhance the maximum mechanical strength [38; 39].  
Although the change from an average of 101 HV (SD = 4.5 HV) for the as-received material to 98 HV (SD = 2 HV) is not significant, it is important to understand that a slight decrease in hardness does not necessarily correlate with a reduction in mechanical strength. As described by various authors [15; 16; 17], the \(\beta\) phases (Mg\({}_{2}\)Si) present in the as-received material become more voluminous and well-distributed after artificial aging. During the aging process, the \(\beta\) phases precipitate and re-distribute within the aluminum matrix, a phenomenon we confirmed using X-ray diffraction (see Section 3.5).  
According to [PERSON] and [PERSON] [40], increasing the aging time enhances re-precipitation, resulting in increased hardness due to the impeded mobility of dislocations caused by precipitate formation. However, prolonged aging can lead to the coarsening of precipitates, reducing their effectiveness as obstacles to dislocation movement and, consequently, decreasing hardness. This balance between precipitate distribution and size significantly influences the material's mechanical properties (see Section 3.4).  
In our case, the observed increase in UTS in the 7 th run sample (293.7 MPa) compared to the as-received material (274 MPa) can be attributed to the better re-distribution and size of the precipitates achieved through our specific heat-treatment regimen. The artificial aging process used in our experiments led to a favorable precipitate structure that enhanced tensile strength without a corresponding increase in hardness. The reduced hardness (98 HV) indicates a more refined precipitate distribution, which can improve the tensile strength by effectively blocking dislocation motion, thereby increasing UTS.  
While the hardness change was minimal, the substantial increase in UTS reflects the successful optimization of the precipitate structure through our heat-treatment process, leading to improved mechanical performance of the alloy.