Bonding Mechanism of Arc-Sprayed ZnAl Coatings on Polypropylene Films: Numerical Simulation of Particle Behavior

Interface microstructures of metallic coatings at end faces are critical for durability of metallic polypropylene (MPP) capacitors. However, the microstructures are difficult to be regulated efficiently due to the specificity of the polymer substrates. Therefore, ZnAl coatings were deposited at end faces of MPP capacitors by arc spraying. The temperature and velocity of in-flight droplets were regulated with different spray distance. A modified numerical simulation with a combustion model was employed to calculate the temperature and velocity of the droplets. The interface microstructures and equivalent series resistance of the capacitors were characterized. The results show that the temperature of the droplets continued to increase during the flight due to exothermic oxidation. The interface of the coatings with the spray distance of 150 mm presented a dendritic microstructure with deeper embedment depth and more bonding layers. The bonding layers reduced as the spray distance decreased to 120 mm because of the damage of the MPP layers. The embedment depth of the coatings decreased as the spray distance increased to 180 mm due to lower temperature of the droplets. The equivalent series resistance of the capacitors decreased to 7.84 mΩ with the dendritic interface microstructures. The research provides a new numerical model to optimize arc spraying and improve the quality of MPP capacitors.