## 2 Materials and Methods  
Al (1050) and Mg (AZ31) billets with a grain size of about 10 \(\upmu\)m were utilized as the workpiece material in this work. Samples of Al and Mg of 12 mm in diameter and with a thickness of 1 mm and 0.3 mm, respectively, were placed in an Al-Mg-Al sequence on Bridgman anvils with grooves in their centers of 12 mm in diameter and a depth of 0.25 mm. The specimens were subjected to high-pressure torsion under 5 GPa of pressure for 10 revolutions at room temperature, as described in [18]. As a result, a disk-shaped Al-Mg sample was obtained with a diameter of 12 mm and a thickness of 0.6 mm. To increase the fraction of intermetallic phases in the nanostructured composite, the HPT sample was annealed in a vacuum at 275 \({}^{\circ}\)C for 30 min. Further analysis of the microstructure and properties was carried out on the surface of the Al-Mg disk. For this purpose, the outer Al layer of the sample was removed by grinding and polishing it until Mg inclusions were revealed on the flat surface. The surface roughness, Ra, was evaluated using an LSM-5 Exciter laser scanning microscope (Carl Zeiss) and found to be lower than 0.3 \(\upmu\)m. The phase composition of the surface was analyzed using a Rigaku Ultima IV X-ray diffractometer using Cu-Ka radiation. The phase content was quantified via Rietveld analysis with an accuracy of 0.1%. The microstructure was examined using a Mira 3 LHM scanning electron microscope (SEM) (Tescan) combined with an energy-dispersive X-ray spectroscopy (EDX) analyzer (Oxford Instruments, Oxford, Great Britain). Al\({}_{3}\)Mg\({}_{2}\) and Al\({}_{12}\)Mg\({}_{17}\) are the main intermetallic compounds formed at the Al-Mg interface in various joining and bonding processes of these light metals [31; 32; 33]. These intermetallic compounds and their structures determine the efficiency of the joint since the precipitation of the Al\({}_{12}\)Mg\({}_{17}\) and the Al\({}_{3}\)Mg\({}_{2}\) phases has a strengthening effect. The WF of the Al-Mg sample was measured as the contact potential difference, obtained via the Kelvin-Zisman method (vibrating electrode technique) [34; 35; 36]. Samples of the initial billets of Al and Mg were utilized for comparison. A platinum plate with an area of 3 \(\times\) 3 mm\({}^{2}\) was used as a vibrating electrode. A low-frequency generator was used to set the resonant oscillation frequency to \(\approx\)200 Hz. An alternating electrical signal was observed between the vibrating electrode and the studied sample when close in distance. The signal was amplified and analyzed using an amplitude-frequency spectrometer. By applying a negative bias voltage to the sample under study relative to the Pt electrode, the signal amplitude in the spectrum decreased from its maximum value to zero. The value of the bias voltage corresponded to the value of the contact potential difference between the Pt electrode and the sample under study. The WF of the studied Al-Mg nanostructured composite was also calculated from the first principles in the framework of the DFT using the plane-wave Vienna Ab initio Simulation Package (VASP) [37]. The first Brillouin zone was sampled with a 20 \(\times\) 20 \(\times\) 10 k-mesh grid, and a vacuum space of 15 A was set in the direction perpendicular to the surface plane. The kinetic energy cutoff for the plane wave expansion was set to 520 eV. All the considered structures were fully optimized until the atomic forces and total energy values were smaller than 10\({}^{-4}\) eV/A and 10\({}^{-8}\) eV, respectively. To determine the sputter rates and yields of the Al\({}_{3}\)Mg\({}_{2}\); Al\({}_{12}\)Mg\({}_{17}\); intermetallic phases; and Al and Mg metals, an Al-Mg sample was subjected to ion irradiation. Irradiation was carried out with argon ions with an energy of 5 keV, normal to the disk surface. The disc was placed in an ion-beam setup with an ion source with a closed electron drift APEL-IS-CELL (Applied Electronics).