Different types of metal substrate, the galvanized process, there are some differences in the method, the need to pay attention to the matter is not the same, the following describes the different base materials, galvanized need to pay attention to the place.
1, cast iron pieces of galvanized
The major problems with cast iron are precipitation difficulties and corrosion after plating. Zinc difficult to attach the main reason is its loose surface texture, a large number of pores and sand to make the surface uneven, in the galvanizing process, the hydrogen easily into the pores, reducing the adhesion of the coating and casting. In addition, cast iron surface hydrogen reaction is strong, zinc ions are not easy to precipitate the reduction reaction. Therefore, the castings need to take a special electro-galvanized pretreatment process in order to get a qualified coating.
2, stainless steel galvanized
Stainless steel has good corrosion resistance, for some special purposes, often in the stainless steel surface of galvanized, stainless steel surface is directly plated to get the poor adhesion of the precipitate. The main reason is the natural state of the surface of stainless steel there is a layer of a solid passive film, affecting the coating adhesion. If galvanization is required, a precoated nickel layer or two galvanizing steps is required to obtain a coating with good adhesion.
3, carburizing steel parts galvanized
Carburized steel after quenching, the surface organization generally contains a large number of fine granular carbides, carbon atoms and trace formation of undissolved carbides on grain boundary pinning role. If the direct plating of the coating is not continuous rough, the quality is poor. It is recommended to first copper-tin alloy, and then electro-galvanized better.
4, zinc alloy die-casting zinc
Die casting surface is a layer of dense layer, the following is a loose porous structure, coupled with the process of segregation of die-casting phenomenon, resulting in pre-plating easily lead to pinholes and stomata, if the die-casting process is inappropriate or unreasonable mold design, Die casting surface cold pattern, shrinkage, loose or pinhole, then the plating process is difficult to obtain a satisfactory coating.
