The integrity of the coating is crucial to the performance and service life of nickel plated parts, and can be guaranteed by a variety of quality inspection methods.
The first is the appearance inspection. Carefully observe the surface of the nickel plated parts with the naked eye or with the help of a magnifying glass to check whether there are obvious defects, such as blistering, peeling, pitting, pinholes, cracks, etc. Experienced inspectors can make a preliminary judgment on the integrity of the coating, but this method can only detect more obvious surface problems and is difficult to detect for subtle defects.
Coating thickness measurement is a key link. A variety of methods can be used, such as coulometric method and X-ray fluorescence method. Coulometric method uses the principle of electrolysis to calculate the coating thickness by measuring the amount of electricity consumed by the electrolytic coating. It has high accuracy and is particularly suitable for measuring small-area nickel plated parts. X-ray fluorescence method is based on the principle that X-rays interact with matter to produce fluorescence. It can quickly and non-destructively measure the coating thickness, and can perform multi-point measurements at different locations to ensure that the uniformity of the coating thickness of the entire nickel plated parts meets the requirements and avoid local integrity damage due to uneven thickness.
Adhesion testing is essential. Commonly used methods include the cross-cutting method and the tensile test method. The cross-cutting method is to use a special tool to cut a grid that intersects horizontally and vertically on the surface of the coating, and then use tape to stick it and tear it off, and observe the shedding of the coating in the grid to judge the bonding strength between the coating and the substrate. If the shedding is serious, it indicates that there is a problem with the integrity of the coating. The tensile test method is to fix a specific tensile device on the coating, gradually apply tensile force until the coating is separated from the substrate, and evaluate the adhesion by measuring the tensile force, providing a quantitative basis for the integrity of the coating.
Porosity detection can also reflect the integrity of the coating. For example, using the filter paper method, a filter paper soaked with a specific detection reagent is attached to the surface of the nickel plated parts. After a certain period of time, the color change of the filter paper is observed. If there are pores, the reagent will react with the substrate metal to change the color of the filter paper. The porosity can be evaluated based on the number and size of the discoloration spots. Too many pores will destroy the integrity of the coating and make the substrate susceptible to corrosion.
Microstructure analysis can be performed with the help of a scanning electron microscope (SEM). It can magnify the surface of nickel plated parts thousands of times or even higher, clearly observe the microscopic morphology of the coating, such as grain size, whether there are microscopic cracks or inclusions, and evaluate the integrity of the coating from a microscopic level, providing a basis for optimizing the nickel plating process.
In addition, corrosion resistance tests such as salt spray tests can also be performed. After the nickel plated parts are placed in a salt spray environment for a certain period of time, the corrosion on the surface of the coating is observed. If rust spots and corrosion pits appear, it means that the integrity of the coating is destroyed and the substrate cannot be effectively protected. This test simulates the actual use environment and can comprehensively evaluate the integrity and corrosion resistance of the coating.
By comprehensively using the above multiple quality inspection methods, the nickel plated parts are comprehensively inspected from multiple aspects such as appearance, thickness, adhesion, porosity, microstructure and corrosion resistance, so as to effectively ensure the integrity of the coating, so that the nickel plated parts meet the use requirements and play their due performance.
