## 3 Results and Discussion
### Sputtering Yield Evaluations  
Figure 6 shows a 3D image and a profile of the Al-Mg sample surface after irradiation, measured with a NanoScan-3D in the atomic force microscopy (AFM) mode. The profile of the sample section is built relative to the initial surface level before the irradiation. The average depth of the etched areas corresponding to the Al matrix was 3.7 \(\upmu\)m, and it was 6.9 \(\upmu\)m for the Mg matrix. The smaller depth value of the Al-etched area was an indication of the lower sputtering rate of Al compared with that of Mg, and this was in agreement with the known data on the sputtering rates of these metals [48]. The depths of the etched sections of the interlayers corresponding to the Al\({}_{3}\)Mg\({}_{2}\) and Al\({}_{12}\)Mg\({}_{17}\) phases were 4.6 and 4.2 \(\upmu\)m, respectively. Therefore, the sputtering rates of these phases were between the sputtering rates of Al and Mg. In this case, the depth of the etched area of the Al\({}_{12}\)Mg\({}_{17}\) phase and, therefore, the sputtering rate of this phase were less than those of the Al\({}_{3}\)Mg\({}_{2}\) phase. The sputtering yield of the Al\({}_{3}\)Mg\({}_{2}\) and Al\({}_{12}\)Mg\({}_{17}\) intermetallic phases was estimated following the expression used to determine the sputtering rate of metals:  
\[\frac{z}{t}=\frac{Mj}{\rho N_{a}e}.Y \tag{1}\]  
where z/t is the sputtering rate; \(M\) is the metal molar weight; \(j\) is the ion current density; \(\rho\) is the density of the metal; \(N_{a}\) is the Avogadro constant; \(e\) is the electron charge; and \(Y\) is the sputtering yield [47]. Based on the fact that the irradiation conditions--in particular, the ion current density and the irradiation time--are the same (i.e., \(j\), \(t\), \(N_{a}\) and \(e\) are constant), then the ratio of the sputtering yields, \(Y_{1}\)/\(Y_{2}\), is proportional to the ratio of the depths of the etched areas, \(z_{1}\)/\(z_{2}\), i.e.,  
\[\frac{Y_{1}}{Y_{2}}=\frac{z_{1}}{z_{2}}.\frac{M_{2}\rho_{1}}{M_{1}\rho_{2}} \tag{2}\]  
The value of the sputtering yield ratio, \(Y_{1}\)/\(Y_{2}\), for Al and Mg calculated from expression (2) was 0.75. Based on [49] and calculations from SRIM-2013 (Stopping and Range of Ions in Matter--a collection of software packages), which are focused on the calculation of many features of the transport of ions in matter [50], the sputtering yield, \(Y\), of Al for argon ions at 5 keV was equal to two. The sputtering yield, \(Y\), of Mg in the same conditions was equal to 2.6. The \(Y_{1}\)/\(Y_{2}\) ratio for Al and Mg, in this case, was 0.77, which was in good agreement with the experimental data. In order to estimate the sputtering yields of intermetallic phases, the sputtering yield of Al was considered to be equal to two. For calculations, the known data on the density of these phases were utilized: \(\rho\)(Al\({}_{3}\)Mg\({}_{2}\)) = 2.25 g/cm\({}^{3}\) and \(\rho\)(Al\({}_{12}\)Mg\({}_{17}\)) = 2.09 g/cm\({}^{3}\). The average molar mass for the phases was considered as follows: \(M\)(Al\({}_{3}\)Mg\({}_{2}\)) = 25.9 g/mol  
Figure 6: AFM image (**a**) and profile (**b**) of the Al-Mg composite surface after irradiation. and \(M\)(Al\({}_{12}\)Mg\({}_{17}\)) = 25.4 g/mol. The calculated sputtering yields of the intermetallic phases, following Equation (2), were found to be \(Y\)(Al\({}_{3}\)Mg\({}_{2}\)) = 2.2 and \(Y\)(Al\({}_{12}\)Mg\({}_{17}\)) = 1.9, respectively. As seen from the calculations, the sputtering yield of the Al\({}_{12}\)Mg\({}_{17}\) phase was even lower than that of the Al. At the same time, the sputtering yields of the Al\({}_{3}\)Mg\({}_{2}\) and Al\({}_{12}\)Mg\({}_{17}\) intermetallic phases, calculated using SRIM-2013, were 2.3 and 2.4, respectively. To explain the reasons for the small (relative to Al) sputtering yield of the Al\({}_{12}\)Mg\({}_{17}\) intermetallic phase, it was important to consider the binding energies of atoms in this phase.