## 2 Materials and Methods  
Simulation of the interaction of the atomizing gas flow with the obstacles (electrodes) was performed using ANSYS CFX simulation [33; 34] based on the solutions of the Navier-Stokes equations under the following boundary conditions: airflow pressure is 0.56 MPa, temperature is 20 \({}^{\circ}\)C, and air density is 1.2754 kg/m\({}^{3}\). Experimental investigation of the airflow dynamic structure was performed through \"shadow\" photographing described in [35]. This method allows obtaining and analyzing gas spectrograms of a gas flow within the area of electrodes' butts (Figure 1). The head of the metallizator (3) was lighted with a point source of light (1). The image of the airflow dynamic structure was projected to the screen (7) and fixed on the photographic film (6). The investigation was carried out without the initiation of the arc; the pressure within the airflow was 0.56 MPa (air consumption was 1.5 m\({}^{3}\)/min). The images were taken using the light-green filter in two mutually perpendicular directions to obtain the \"side view\" and the \"top view\" of the electrodes.  
Regarding the periodic character of accumulation and extraction of liquid metal on electrodes' butts, a periodic supply of atomizing air was proposed due to the surface tension forces. The aim was to provide an opportunity for the accumulation of liquid metal on the electrodes' butts with a limitation of air influence upon the droplets. Impulse air supply was provided by means of a rotation valve-based pulsator (4) (designed by the author of this article) intended for controlled airflow interruption. The pulsator was integrated into the compressed air supply system and installed directly before the metallizator (1) (Figure 2). The pulsator valve was connected with the electric (7) motor's shaft through the elastic coupling (6). The frequency of interrupting airflow was controlled by the rotation speed of the motor's (7) shaft. For the pulsation frequency counting, a light diode (8) was used, providing a light beam passing through the window in the rotating disc (5) to reach the light-receiving element (9). The pulses were fixed using an oscilloscope (10).  
Electric-arc spraying was carried out using an EM-17 metallizator, equipped with the above appliance for pulsating air supply. The aluminum wire of grade ESAB OK Autrod 5356 with a 2.5 mm diameter was used as an electrode. The coatings were deposited on plates 100 \(\times\) 100 \(\times\) 7 mm in dimension, made of mild steel. The parameters of the EAS regime were: arc amperage--100 A, arc voltage--30 V, wire feeding--80 mm/s, an air consumption--1.5 m\({}^{3}\)/min, airflow pressure at the nozzle's edge--0.56 MPa, the distance to the target--170 mm, and the velocity of surface spraying--6 m/min.  
Figure 1: Sketch of the installation for obtaining the gas spectrograms: 1—light source; 2—objective lens; 3—metallizator head; 4—compressed air supply; 5—support; 6—photographic film, 7—screen.  
Figure 2: The appliance for controlling pulsations of atomizing airflow: 1—electric-arc metallizator; 2—the wire holder; 3—air supply; 4—pulsator; 5—opening disc; 6—elastic coupling; 7—electric motor; 8—light source; 9—light-receiving element; 10—oscilloscope.  
The coatings' microstructure was characterized using an optical microscope Optika IM-3 Met on transverse microprobes prepared by the standard metallographic procedure of polishing to a mirror surface and etching by 4 vol. % nital reagent. The images of the structure were applied to calculate the volume fraction of the oxides using the Rosival method [36]. For each EAS regime, five images of 50 m\({}^{\prime}\)60 mm squared were used with further averaging the results.