Composite plating can be divided into the following three types according to the different deposition methods.
(1) The microparticles are used as the dispersed phase to suspend them in the plating solution for electrodeposition or chemical deposition. This method is called the dispersion deposition method.
(2) When the particles are large or heavy, the particles are deposited on the surface of the substrate first, and then fill the gaps between the particles with the precipitated metal. This method is called the deposition eutectoid method.
(3) The long fibers are buried or wound on the surface of the substrate and then deposited. This method is called the buried deposition method.
It is customary to call the first two methods composite plating, while the latter method is called fiber reinforced composite plating.
The process of composite plating is an organic combination of physical and chemical processes. It is generally believed that in the case of dispersion composite electroplating, the co-deposition process of particles and metal is divided into the transportation of particles in the plating solution to the vicinity of the cathode surface, the adsorption of particles on the surface of the metal to be plated, and the discharge deposition of metal ions on the cathode surface to form a lattice and bury the solid particles into the metal layer, several steps. The eutectic particles form an irregularly distributed dispersed phase in the deposited metal. In fiber-reinforced composite plating, the coiled long fibers exhibit a regular arrangement. Electroless plating can also produce high-quality composite coatings.
The transport of particles to the vicinity of the cathode surface mainly depends on the stirring method and intensity of the bath, as well as the shape and arrangement of the cathode. The adsorption of particles on the cathode surface is affected by various factors such as the force between the particles and the electrode, such as the characteristics of the particles and the electrode, the composition and performance of the plating solution, and the operating conditions of electroplating. In general, only when the thickness of the metal layer around the particle is greater than half of the particle size, the particle is considered to be embedded with metal. Therefore, the adsorption degree of the particles on the surface of the cathode, the impact of the flowing solution on the particles on the cathode, and the speed of metal electrodeposition will all affect the embedding of the particles in the matrix metal.
To prepare an ideal composite coating, not only the particles and fibers are required to be stable, but also should not promote the decomposition of the plating solution. The particle size of the particles or the diameter of the fibers should be appropriate, usually 0.1 to 10 μm, but preferably 0.5 to 3 μm. In addition, proper stirring is also essential.
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