## 5 Discussion  
It is known that alternating current TIG welding of aluminium alloys is accompanied by so-called cathodic cleaning to break up the surface oxide layer. The high arc energy also leads to the partial disintegration of the ceramic reinforcing phase of the fused parent metal and contributes to the formation of harmful products that impede the wettability of the ceramics through the metal matrix [58]. Thus, the addition of alloying elements to improve weldability, reducing the amount of eutectic phase and changeing the crystallisation mode from dendritic to fine-grained appears to be an effective way to improve weld quality in composite materials. This can minimise the process of ceramic particles being pushed out by the growth of the dendritic crystallisation front, thereby changing the mechanical properties of the welded joint [13]. The modification of the AlMg5 alloy by the addition of scandium or zirconium changed its structural structure. Dispersion of the intermetallic phase Al\({}_{3}\)Sc in AlMgSc alloys or Al\({}_{3}\)Zr in AlMgZr alloys forms the nucleation pads of fine grains. The fine-grained structure and secretion strengthening favourably shape the course of weld pool crystallisation, resulting in good mechanical weld properties close to those of the parent material [59; 60]. Tests carried out on AlMgZr and AlMgSc alloys have shown that:  
1. The addition of zirconium to the AlMg5 alloy reduced dendritic grain growth and, through Al\({}_{3}\)Zr precipitates, improved its mechanical properties;
2. The zirconium in the alloy formed two types of precipitates in the casting. One was in the form of \"sticks\" and the other in the form of dobby precipitates unevenly \begin{table}
\begin{tabular}{l c c c c c c c} \hline \hline
**Filling Material** & **Initial Energy [J]** & **Specimen Length [mm]** & **Specimen Width [mm]** & **V Notch Depth [mm]** & **Impact Energy [J]** & **Impact Strength [J/cm\({}^{2}\)]** & **Standard Deviation** \\ \hline AlMg5 Zr0.35 & & & & & 4.829/775 & 12.07444 & 0.222583 \\ AlMg5 Zr0.67 & 49.03325 & \(10\) & \(10\) & \(2\) & 4.780/43 & 11.95185 & 0.367749 \\ AlMg5 Zr0.93 & & & & & 4.805259 & 12.01315 & 0.346717 \\ \hline AlMg5 Sc0.30 & & & & & 4.780742 & 11.95186 & 0.200849 \\ AlMg5 Sc0.61 & 49.03325 & \(10\) & \(10\) & \(2\) & 4.903325 & 12.25831 & 0.190333 \\ AlMg5 Sc0.84 & & & & & 4.927842 & 12.31961 & 0.174729 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Impact test results for as-cast filler materials. distributed in the eutectic near grain boundaries, which had the effect of increasing hardness and microhardness;
3. The addition of Sc to AlMg5 alloys changed the structure of the casting to a fine-grained structure. This effect was most pronounced with the content of this element corresponding to the eutectic value for the Al-Sc two-phase alloy;
4. The Al\({}_{3}\)Sc precipitates distributed in the central part of the grains and in the form of very small precipitates along the grain boundaries visibly reduced the amount of the eutectic phase. This alloy structure increased the tensile strength;
5. Considering the results obtained from the tests carried out, it can be seen that the addition of scandium improved the mechanical properties of the AlMg alloys to a greater extent than had the zirconia modification. Furthermore, it is known that the addition of scandium significantly increases corrosion resistance and improves weldability [44; 45; 46; 47]. The only aspect that may cause a limitation in the wider use of this element as a modifier of AlMg alloy-based filling material is its high price. Therefore, zirconium, although offering slightly inferior mechanical properties, is less expensive and can also be used as an alloying additive to improve the mechanical properties of TIG welded joints. Conceptualisation, J.W. ; methodology, J.W. ; software, M.S. ([PERSON]); validation, J.W., A.T., M.S. ([PERSON]) and M.S. ([PERSON]); formal analysis, J.W. ; investigation, A.T.; resources, J.W. and M.S. ([PERSON]); data curation, M.S.