A mathematical model for studying temperature-time conditions of arc surfacing upon manufacturing of steel-aluminum compositions has been developed and verified. During simulation, the dependences of the thermophysical properties of the materials under study (thermal conductivity and heat capacity of a unit mass of the substance at constant pressure and volume) on the heating temperature were added to the database of the «SVARKA» software to solve the thermal problem. When simulating the arc surfacing, the geometric model of the object was set in the form of a single body, which, e.g., in case of formation of functional coatings based on non-ferrous alloys on steel substrates, can consist of various materials. The parameters of the heat loads of the heating source are: the advance speed, power, distribution along and across the weld, as well as the presence and grade of the filler material. The calculation of heat propagation upon argon-arc surfacing with a non-consumable electrode was carried out according to the scheme with a normal-circular heat source located on the surface of a flat layer with the limiting effect of the bottom plane of the sheet. The considered calculation scheme includes all the main features of the argon-arc surfacing process, i.e., introduction of the heat of the welding arc into a massive body from the surface; small pressure of the welding arc; slight immersion of the active arc spot in the liquid metal. It is shown that allowance for the thermophysical properties of the intermetallic layer of the Fe – Al system located in the diffusion zone, provided determination of the heating temperature with the uncertainty of no more than 8 % not only at the steel-aluminum interface, but also at any point of the samples both in the transitional bimetallic steel-aluminum elements joined with aluminum or steel structures, and in functional aluminum coatings formed by surfacing, including those made of composite materials.