## 1 Introduction  
The wide application of magnesium is limited by its low corrosion resistance. During the last decade, many researches have focused on the effect of the metal microstructure and medium on the magnesium corrosion behavior [1; 2; 3; 4]. The standard magnesium electrode potential is \(-\)2.363 V (vs. normal hydrogen electrode (NHE)), whereas the stationary magnesium potential and its alloys is set at \(-\)1.3 V. This difference in potentials and dissolution patterns indicate a passive state of magnesium in neutral electrolyte solutions. In this case, the passivating surface layers can be sparingly soluble oxide and magnesium hydroxide. There are several researches devoted to the mechanism of corrosion of pure magnesium in aqueous solutions [2; 3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25]. Special attention should be given to the excellent review in [25]. In many works [3; 4; 5; 12; 16; 21; 22; 24; 25], the corrosion film on magnesium in different solutions is presented as a two-layered one. It consists of a thin dense layer of the MgO adjacent to metal and friable hydroxide on its surface, at the same time oxide is the main barrier layer. In [27], the relationship of the roles of these two layers using representations of their interaction with the electrolyte solution is presented in detail. Its formation is connected with metal background, i.e., with formation of the primary dense film at preparing the surface in air [4; 16] and dissolution of metal is supposed only on the sites of metal which are free of MgO [5]. However, the microelectrode surface scanning data presented in the same work demonstrated a change in surface resistance in a very narrow range, whereas its value varied only one and a half times. Such a difference is hardly able to characterize the difference between a surface with a dense magnesium oxide film and without it, especially considering the declaration of corrosion blocking by that film. In some works, referred to direct study of the transverse structure of the corrosion film, its two-layer character was presented quite clearly [3; 4; 22; 24; 27]. The question of monovalent magnesium role in corrosion process is insufficiently clear as well as, except for its participation in formation of negative difference effect (NDE) [5; 7; 12; 14; 16], where, as a rule, it gets the role of intermediate short-living particle causing the emergence of NDE. There are lots of researches dedicated to the effect of electrolyte composition on magnesium corrosion [5; 6; 9; 10; 11; 14; 19; 22; 23; 26; 27], where the effect of both anions, and cations on the corrosion process was described. Thus, [PERSON] et al. [17] studied the electrochemical behavior of magnesium in chloride- and sulfate-containing solutions and concluded that the presence of chloride ions accelerated the electrochemical reaction of the transition of metal magnesium to monovalent one. Sulfate ions were shown to possess less effect than chloride ions [8; 17]. The ammonium salt is considered to be one of the strongest factors affecting the corrosion activity of magnesium [27]. It is assumed that the strong solvent effect of the ammonium cation appears on the dense part of the magnesium oxide film, which leads to its depassivation and corrosion. A significant number of works are also devoted to the pH effect on the corrosion process [3; 11; 15; 22; 23; 27]. The nature of the pH effect on the corrosion process through the influence at the stage of hydration of magnesium oxide and recrystallization of its hydroxide is most fully disclosed in [22]. Almost all researches of the corrosion process on magnesium as a rule use methods of investigation of electrochemical corrosion by particular polarization dependencies, sometimes supplemented with electrode impedance analysis. As a rule, the application of these methods is not accompanied by proof of the possibility of using certain equivalent schemes and approaches in the study of polarization dependencies. In some works, Ref.