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The paper presents a study of the structure-phase state of aluminised coatings obtained by the electrospark alloying (ESA) method. The influence of the discharge energy and the productivity of the treatment process on the thickness of the hardened layer, its microhardness, continuity and surface roughness of C20 and C40 steels has been studied. It is shown that the structure of ESA coatings consists of a white layer, a diffusion zone and a substrate metal. Increasing the discharge energy during ESA leads to a change in the chemical and phase composition of the layer. With a 2-fold decrease in ESA productivity, the thickness of the “white” layer increases to 75 to 110 µm, its microhardness to 7450 MPa; the continuity of the coating tends to 100 pct. With a 4-fold decrease in ESA productivity, the thickness of the ‘white’ layer also increases, but not intensively, to 60 µm at Wp = 4.6 J and then does not change; at the same time, the surface roughness Ra increases to 8.1 to 9.0 µm and the continuity is 95 pct. A 4-fold decrease in process productivity contributes to the deterioration of coating quality parameters and an increase in roughness. The study of the influence of the energy parameters of ESA, as well as the alloying time (‘productivity’) of the process, is important for the improvement of hardening technology. The paper proposes a mathematical model for predicting the coating parameters taking into account the processing time of a given plane to be alloyed, i.e., the labour intensity of the ESA process (the value of the inverse productivity). The equations of the mathematical model and methods for determining the constants of the equations for predicting the parameters of the alloyed layer have been obtained. An algorithm has been developed and the adequacy of the mathematical model has been verified, which allows the prediction of the main technological parameters of ESA in order to obtain a coating with the specified quality indicators.