existElectroplated zinc nickel processingDuring the process, preventing the occurrence of pores and pitting in the coating requires control from multiple aspects. The following are specific measures:
pretreatment
Degreasing and degreasing: Ensure that the surface of the workpiece is free of oil stains, grease, and other pollutants. Organic solvent degreasing, alkaline degreasing, or electrochemical degreasing methods can be used. If oil removal is not felt, the grease will hinder the contact between the plating solution and the workpiece surface during the electroplating process, causing hydrogen gas to accumulate in these areas, thereby forming pores and pitting.
Acid pickling rust removal: effectively removes rust and oxide scale on the surface of the workpiece, ensuring good adhesion between the coating and the substrate. Excessive or insufficient acid washing can affect the quality of the coating. Excessive acid washing can increase the surface roughness of the workpiece, making it easy to accumulate dirt and grime, leading to porosity and pitting; Insufficient acid washing can lead to residual surface oxide scale, hindering the normal deposition of electroplated layers.
Water washing process: prevent residual pre-treatment solution from entering the plating solution. Residual acid, alkali and other substances may react with the plating solution, changing the composition and properties of the plating solution, affecting the precipitation of hydrogen gas and the crystallization process of the coating, thereby producing pores and pitting.
Composition and maintenance of plating solution
Main salt concentration: Maintain the concentration of zinc and nickel salts in the plating solution within a reasonable range. Excessive or insufficient concentration can affect the crystallization process and performance of the coating. For example, a high concentration of main salt may lead to coarse crystallization of the coating, which is prone to porosity; If the concentration is too low, it will slow down the deposition rate of the coating, and the hydrogen gas will stay on the surface of the workpiece for too long, increasing the probability of pore formation.
Additive usage: Reasonably add brightening agents, wetting agents, and other additives. Brightening agents can improve the appearance and glossiness of coatings, but excessive use may lead to increased internal stress in coatings, which can easily result in porosity and pitting; Wetting agents can reduce the surface tension of the plating solution, making it easier for hydrogen gas to escape from the surface of the workpiece and reducing the formation of pores. Therefore, it is necessary to strictly control the types and amounts of additives, and conduct regular analysis and supplementation.
Purification of plating solution: Regularly filter and purify the plating solution to remove solid impurities, oil stains, and organic decomposition products from the plating solution. These impurities will adsorb on the surface of the workpiece, hindering the normal deposition of metal ions, and also affecting the escape of hydrogen gas, leading to the formation of pores and pitting. Purification of plating solution can be achieved through methods such as activated carbon adsorption and filter filtration.
Control of electroplating process parameters
Current density: Choose an appropriate range of current density. Excessive current density will enhance cathodic polarization, causing a large amount of hydrogen gas to precipitate on the cathode surface. If it cannot escape in time, pores will form; If the current density is too low, it will result in slow deposition rate of the coating, low production efficiency, and easy occurrence of uneven coating. Therefore, it is necessary to adjust the current density reasonably based on factors such as the material, shape, size, and composition of the plating solution of the workpiece.
Temperature control: Control the temperature of the plating solution within an appropriate range. Excessive temperature can cause the water in the plating solution to evaporate too quickly, resulting in changes in the composition of the plating solution. At the same time, it can also reduce the solubility of hydrogen gas, making it easy to form pores in the coating; If the temperature is too low, the conductivity and dispersibility of the plating solution will decrease, the crystallization of the coating will become coarse, and it is also prone to porosity and pitting. Generally speaking, it is advisable to control the temperature of the plating solution for electroplating zinc and nickel at around 40-60 ℃.
Mixing method: Adopt appropriate mixing method and mixing intensity. Stirring can evenly distribute metal ions in the plating solution, improve the dispersion ability of the plating solution, and also facilitate the escape of hydrogen gas. However, excessive stirring intensity may disrupt the airflow on the surface of the workpiece, causing hydrogen to accumulate locally and form pores; If the mixing intensity is too low, it cannot achieve sufficient mixing. Mixing can be carried out using methods such as air agitation, mechanical agitation, or cathode movement. The specific mixing method and intensity should be optimized according to the actual situation.
Equipment and Operating Standards
Anode state: Ensure the normal dissolution and good surface condition of the anode. Uneven anodic dissolution or passivation film on the anode surface can lead to uneven distribution of metal ion concentration in the plating solution, affecting the quality of the coating. At the same time, gas may also be generated, causing pores and pitting. Regularly inspect the anode and promptly replace or dispose of damaged or passivated anodes.
Hanging fixture design: Design a reasonable hanging fixture to ensure that the workpiece is in full contact with the plating solution during the electroplating process, and the current distribution is uniform. The conductivity of the hanger should be good to avoid local overheating or abnormal current density caused by poor contact, which can lead to the appearance of pores and pitting. At the same time, the shape and structure of the hanger should facilitate the escape of hydrogen gas and prevent hydrogen gas from accumulating around the workpiece.
Operating standards: Operators must strictly follow the electroplating operating procedures to avoid problems caused by improper operation. For example, the process of inserting and removing workpieces from the groove should be carried out slowly to prevent splashing of the plating solution and the generation of surge current; During the electroplating process, it is necessary to maintain a clean operating environment and avoid impurities such as dust and oil from entering the plating solution.
