## 4 Discussion  
Presented in Figure 9, aluminum oxidation behavior under the EAS process with the airflow pulsation is explained by the action of two oppositely affecting factors. The steady oxidation-reduction at an increase in the pulsation frequency up to about 65 Hz is caused by the fact that the time interval between the air impulses is smaller than the time of accumulation of liquid metal on electrodes' butts; thus, air is missing within the depression area. As a result, the droplets of molten metal are forming with virtually no contacting oxygen. Starting from about 65 Hz, the pulsation frequency increase resulted in a growth in the oxidation rate, which can be ascribed to the fact that at a high pulsating frequency, the flow behavior approaches that of a steady flow. That is, the high pulsation frequency has almost no influence on the flow gas dynamics. This can be explained by the effect of the pulsation frequency on the curvature radius of molten metallic droplets forming at the electrode butt (the droplet size is important since it determines the area of liquid metal that contacts with the airflow oxygen). This approach is outlined in [39], where the mass transfer of electrode metal under the airflow pulsation was analyzed, and the conditions of the detachment of molten metal from the electrode were studied. According to [39], the curvature radius of a droplet (\(R_{cur}\)) can be calculated by the equation:  
\[R_{cur}=\frac{v_{el}}{2f\sin^{2}(arctg\frac{2v_{el}\sin\omega}{fd_{di}})} \tag{1}\]  
where \(v_{el}\)--electrode feeding velocity, \(f\)--pulsation frequency, \(w\)--angle between the electrodes, \(d_{d}\)--diameter of the electrode. Figure 9: The effect of the pulsating frequency of the airflow upon the oxide volume fraction in the coating deposited with aluminum wire. Equation (1) was applied to evaluate the effect of the pulsation frequency under the following parameters: \(v_{d}\) is 40-100 mm/s, \(w\) is 30 degrees, and \(d_{el}\) is 2.5 mm. The dependence of \(R_{cur}\) on the pulsation frequency is illustrated in Figure 10. It can be seen that with a growth in the frequency of the pulsations, the value of the curvature radius steadily increases due to a reduction in the thickness of the liquid layer. It is noteworthy that with the feeding rate increase, the curvature radius grows with less intensity, i.e., the feeding rate promotes the fine (of low radius) liquid droplet formation. This is because growth in the feeding rate is accompanied by a voltage growth leading to an increase in the mass of molten metal and thickness of the liquid layer. At the optimal flow pulsation (65 Hz) frequency, the liquid metal can form a droplet of low curvature on the electrode's butt during the pause between the air pulses; thus, the droplet is detached by each airflow pulse. At a higher frequency, there could be a case when liquid metal is not accumulated enough to form a droplet, so it is detached by some subsequent air pulse. This means that the liquid metal stays on the electrode's butt between the air pulses being subjected to the oxidation, i.e., metal oxidation is not reduced. Thus, the frequency of a droplet formation should match the frequency of the airflow pulsation in order to minimize the metal oxidation at the electrode's butt. The results of gas-dynamics investigations showed that the pulsating airflow transports the molten droplets as stable as the steady flow, i.e., with straight-line particles' movement. One can state that introducing the pulsator into standard metalizing equipment does not violate the arc burning stability at any frequency of the flow pulsation. The application of a pulsating supply of atomizing air is favorable for resource saving since the air pulsation allows the metal oxidation to decrease, thus decreasing the loss of alloying elements, which burn out in atomizing airflow. Accordingly, the content of alloying elements in the electrode can be corrected (reduced), leading to lower production costs.