Research On Preparation And Characteristic Of Cold-sprayed Coating For The Splash Zone Corrosion And Protection

Marine environment is extremely brutal, suffer serious corrosion problems to offshore steel structures(such as ships, offshore platforms, harbor engineering facilities, etc.), with the flash zone being the most serious, which affects the normal operation of the equipment. Marine anti-corrosion measures currently used in the metal coating is the most effective means. Al and Al-Zn coating is commonly used, such coatings in the marine environment can be used as an anode coating, and can play the role of corrosive medium and matrix isolation, so it has a broad application prospects.This paper will use CFD software to optimize nozzle size parameters and to change throat diameter of the nozzle and in the time of determining throat diameter of 4mm and, length expansion of 70 mm, it simulated flow velocity under different outlet diameter, temperature, pressure, Mach number relation, and analyses the velocity cloud picture in the internal diameter and the outlet. By comparison, it can be found that when the outlet diameter is 8mm results are optional, and divergence ratio is 4. Both internal and external air speed is smooth, no significant shock occured. If the machining process is feasible, the longer the length of expansion of the nozzle is, the larger the velocity of the particles in the exit is.The extent of divergence of particles can be limited to some extent at the same time.Coating composition with seven different compositions of cold spraying Al, Al-Zn, Al-5Al2O3, Al-Zn-Al2O3 and so on have been prepared in the paper. If good particle circulation is guaranteed, coating produced by smaller particle size has a higher density, lower porosity, higher degree of being changed and more smooth surface. As for cold spraying Al-Zn coating, the larger the proportion of the Zn content in the coating is,the smoother the coating surface is,and the thickness is smoother,the porosity is lower as well.Despite the hardness of the coating has been improved, the thickness of the coating is very restricted From the cold spraying Al-50%Al2O3, Al-Zn-50%Al2O3 coating analysis point of view:Add a certain percentage of Al2O3 particles can make Al particles deform sufficiently,while Al2O3 particles have no obvious distortion. But, there are a small amount of broken Al2O3 particles in the coating. From the aspect of the whole coating, in addition to the damage caused by defects of high density, low porosity in Al2O3 particles, Al2O3 particles appeared grain refinement phenomenon, which will largely improve the coating bond strength and hardness.By observing the transformation of surface and across-section after the corrosion of coating surface, it can be found that serious corrosion have taken place. From the analysis of the changes of the corrosion potential o, it can be known that the corrosion potential of cold spraying Al-50%Zn coating is most stable, at around From the variation trend of the three linear polarization resistance of the coating, when the immersion time increases, the resistance will come to stabilize after its instant.Research on polarization curves shows that the initial self-corrosion electricity is the largest, it come to decrease as the extension of time. Passivation take place earlier, which indicate that Zn behave corrosion. In the late period of immersion, the self-corrosion electricity is maximum, indicating corrosive medium penetrates into the interior corrosion and behave rapid corrosion.