The aluminised coatings obtained on steels by the method of electrospark alloying (ESA) are investigated. Carbon steels were tested for the influence of the discharge energy and productivity (classic regimes, 2- and 4-fold reduction values) of the treatment process on the thickness of the hardened layer, its microhardness, continuity and surface roughness. Optical and scanning metallography, X-ray diffraction analysis, micro-X-ray diffraction analysis and micro hardness distribution tests were used for the study. Metallographic analysis showed that the structure of ESA coatings is layered, with a white layer not detectable in the reagent, diffusion zone or the substrate. The chemical and phase composition of the coating change when the discharge energy is increased during ESA. At low discharge energies, a layer consisting mainly of a-Fe and aluminium oxides is formed; as the discharge energy rises, the layer consists of iron and aluminium intermetallics and free aluminium. If the ESA productivity is reduced by factor 2, the thickness of the "white" layer increases to 75–110 µm, and its microhardness to 7450 MPa; the continuity of the coating approaches 100%. The deterioration of the coating quality parameters and the increase in roughness are due to a 4-fold decrease in process productivity. In order to improve hardening technology, it is important to study the influence of the energy parameters of ESA and the alloying time ('productivity') of the process. Aluminum-based coatings produced by the proposed ESA methods are recommended for use at high temperature.