## 2 Materials and Methods  
Once the weight ratios of the alloy in preparation were established, the individual components were subjected to weighing. Components with elevated purity of 4N were specifically chosen for the production of solder. The production of solder in its liquid state occurred within an induction oven. The process unfolded in the following manner: The designated mixture was placed into a crucible. Subsequently, Zn was heated to a temperature of 700 \({}^{\circ}\)C, leading to its melting and complete fusion. Magnesium was wrapped with tin foil and immersed into the zinc melt. The molten material was poured into a graphite vessel, and this casting process was conducted without the application of a shielding atmosphere. The chemical composition of the soldering alloy, as outlined in Table 1, was experimentally determined. The chemical analysis was carried out using atomic emission spectrometry with induction coupled plasma (ICP-AES). The analysis was performed utilizing the Spectro Vision EOP instrument. Prior to the ICP-AES analysis, the alloy samples underwent dissolution in appropriate chemical solutions composed of bases and acids. The analysis itself occurred on an emission atomic spectrometer featuring a pneumatic atomizer and sputtering chamber. A specimen intended for the tensile test was precisely machined from the soldering alloy, as illustrated in Figure 1. The dimensions of the test piece in millimeters are shown in the same figure. The resulting tensile strength of the solder test specimen was 95 MPa, shown in Figure 2. From the graph, it can be seen that the yield strength of the solder was approximately 59 MPa. The experiments utilized substrates composed of the subsequent materials:  
* Ceramic SiC substrate in the form of discs with dimensions \(\mathcal{O}\) 15 \(\times\) 3 mm,
* Cu substrate of 4N purity machined into dimensions \(\mathcal{O}\) 15 \(\times\) 2 mm and 10 \(\times\) 10 \(\times\) 2.5 mm. Figure 2(a) illustrates the schematic representation of soldered joints created for the purpose of chemical analysis at the solder/substrate interfaces. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multicolumn{2}{c}{**Charge [wt. \%]**} & \multicolumn{2}{c}{**ICP-AES [wt. \%]**} \\ \cline{2-5}  & **Zn** & **Mg** & **Zn** & **Mg** \\ \hline Zn3 Mg1.5 Sr & 98.5 & 1.5 & 96.04 & 1.24 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The formation of Zn-Mg alloy and the chemical analysis results by ICP-AES method [wt. %]. Figure 1: A solder test specimen designed for tensile strength testing. Fabrication of joints involved the use of a thermostatically controlled hot plate. On the hot plate, the SiC substrate was positioned, followed by the application of solder, and then heated to the designated soldering temperature. Soldering was carried out employing ultrasonic equipment, specifically the Hanuz UT2, with parameters detailed in Table 2. Activation of the solder was achieved using an enclosed ultrasonic transducer consisting of a piezo-electric oscillating system and a sonotrode made out of titanium with \(\O\) 3 mm end tip. The soldering temperature, set at 380 \({}^{\circ}\)C, was consistently monitored using a NiCr/NiSi thermocouple on the hot plate. The ultrasonic power was applied for a duration of 5 s. The soldering process was conducted without the use of flux. Using ultrasonic activation, any surplus oxide layer on the solder surface was removed. A similar procedure was undertaken with the second substrate. Substrates, each bearing molten solder, were then aligned and combined to form the joint. The procedural representation is illustrated in Figure 4.  
Figure 3: Assembly of soldered joint (**a**) for the substrate/solder boundary analysis and (**b**) for the measurements of shear strength. Figure 2: Tensile strength test of the solder Zn1.5 Mg. The metallographic preparation of samples from soldered joints adhered to standard procedures commonly employed for specimen processing.