# Numerical Simulation of Liquid Film Characteristics during Atomization of Aluminum Alloy Powder
## 3 Simulation Results and Discussion
### Comparative Analysis of Velocity and Pressure Distribution on Different Disk Surfaces
When the speed of the liquid film increases to a certain value and the thickness of the liquid film decreases to a certain value, the resultant force of the stress on the liquid film is sufficient to overcome the surface tension of the molten metal, resulting in the splitting of the continuous liquid film. The edge of the critical liquid film is partially raised and gradually extended to form a liquid filament, which is defined as primary crushing. After further observation and analysis of the liquid film separated into liquid filaments on the rotating disk, as shown in Figure 9, it can be seen that the liquid filaments maintain continuous motion under the comprehensive action of the supporting force, gravity, centrifugal force, friction force, and molten metal surface tension on the disk surface. However, when the liquid filament reaches the edge and continues to move to the outer area of the disk, it becomes unstable and is broken into small droplets after moving away from the disk edge, completing the secondary crushing. The atomized broken droplets travel in a cool inert atmosphere, shrink and spheroidize, and then solidify to form a powder, which completes the atomization process. On the basis of the above numerical simulation, the self-developed centrifugal atomization experimental device was used with a flat disk and spherical disk with the same structure and size, as in the numerical simulation. AlSi10 Mg, which is the most used material in the field of additive manufacturing, was selected as the research material for experimental verification. After the preparation of the experimental device, the atomization chamber was evacuated and filled with nitrogen after the vacuum degree reached \(1\times 10^{-2}\) Pa. The atmosphere preparation was completed if the oxygen content was less than 500 PPm as detected by the online oxygen meter, and then the atomization experiment was started. The method can be described as follows. The AlSi10 Mg alloy was added to the melting furnace, we heated the alloy into a melt, and then the molten metal was sent to the induction heating tundish at the upper part of the atomization chamber. The molten metal was delivered to the atomizing rotating disk through the guide tube at the bottom of the induction heating tundish. We adjusted the speed of the high-speed motor to 10,000 rpm and drove the atomization rotating disk to break the molten metal into uniform and stable metal droplets under the action of centrifugal force. After atomization, the atomization disk was removed for photo analysis. The experimental results are shown in Figure 10. The experimental results show that the diameter of the continuous liquid film boundary of the flat disk is 35 mm, and that of the continuous liquid film boundary of the spherical disk is 42 mm. Although there is a slight error in the simulation results, the diameter of the continuous liquid film boundary of the spherical disk is larger than that of the flat disk, and the liquid filaments produced by the liquid film splitting on the rotating disk are thinner and more numerous, which proves the accuracy of the simulation and its conclusion. Figure 9: Cloud diagram of liquid film spreading and breakage in different disk atomization processes. (**a**) Flat disk; (**b**) spherical disk. The velocity distribution characteristics of the liquid film on different disk surfaces under the working condition of 10,000 rpm were further analyzed on the basis of the above research. As shown in Figure 11, the velocity distribution of the molten fluid film on the surface of the flat disk, as well as the radial and tangential velocity distributions, shows that the liquid film velocity, including the radial and tangential velocity of the flat disk, increases with the increasing diameter, and the liquid film gradually accelerates along the radial direction under the action of centrifugation. In other words, the inner circle velocity is relatively small, the outer circle velocity gradually increases, and the maximum velocity is reached at the outer edge.