Electroplating is a surface treatment process that uses electrochemical properties to deposit the required metal cladding on the surface of the plating part.
Electroplating principle: In a salt solution containing the metal to be plated, the plated matrix metal is used as the cathode. Through electrolysis, the cations to be plated in the plating solution are deposited on the surface of the matrix metal to form a coating.
Purpose of electroplating: To obtain a surface layer that is different from the matrix material and has special properties to improve the corrosion resistance and wear resistance of the surface.
The thickness of the coating is generally from a few microns to dozens of microns.
Characteristics of electroplating: The electroplating process and equipment are relatively simple, the operating conditions are easy to control, and the coating materials are extensive and the cost is low. Therefore, it is widely used in industry and is an important method for material surface treatment.
Classification of coatings
There are many types of coatings, which are classified according to their performance as follows:
(1) Protective coatings: such as zinc, zinc-nickel, nickel, cadmium, tin, etc., as anti-corrosion coatings that are resistant to the atmosphere and various corrosion environments.
(2) Protective-decorative coating: For example, Cu-Ni-Cr coating, is both decorative and protective.
(3) Decorative plating: such as Au and Cu-Zn imitation gold plating, black chromium, black nickel plating, etc.
(4) Wear-resistant and wear-reducing coatings: such as hard chromium coating, loose hole coating, Ni-Sic coating, Ni-graphite coating, Ni-PTFE composite coating, etc.
(5) Electrical performance coating: For example, Au coating, Ag coating, etc., not only have high conductivity, but also anti-oxidation, which can avoid increasing contact resistance.
(6) Magnetic coating: For example, the soft magnetic coating includes Ni-Fe coating and Fe-Co coating; hard magnetic energy includes Co-P coating, Co-Ni coating, Co-Ni-P coating, etc.
(7) Weldable coating: such as Sn-Pb coating, Cu coating, Sn coating, Ag coating, etc. It can improve weldability and is widely used in the electronics industry.
(8) Heat-resistant coating: such as Ni-W coating, Ni coating, Cr coating, etc., with high melting point and high temperature resistance.
(9) Repair coating: Some high-cost wearable parts, or processed ultra-poor parts, using electroplating to repair dimensions can save costs and prolong their service life. For example, the Ni, Cr and Fe layers can be repaired.
According to the electrochemical properties between the coating and the matrix metal, it can be divided into anode coating and cathodic coating. When the potential of the coating relative to the matrix metal is negative, the coating is anode, which is called anode coating, such as the galvanized coating on steel. When the potential of the coating relative to the matrix metal is positive, the coating is a cathode, which is called a cathodic coating, such as the nickel coating and tin coating on steel.
According to the combined form of coating, the coating can be divided into: single-layer coating, such as Zn or Cu coating; multi-layer metal coating, such as Cu-Sn/Cr coating, Cu/Ni/Cr coating, etc.; composite coating, such as Ni-Al2O3 coating, Co-SiC coating, etc.
If classified according to the composition of the coating, it can be divided into a single metal coating, alloy coating and composite coating.
