The selection principle of coating mainly depends on the following factors:
(1) The type and nature of the covered metal;
(2) The structure, shape and dimensional tolerances of the metal parts;
(3) The use and working conditions of the metal parts;
(4) The nature and application of the coating.
1. Select according to the base material
(1) Precious metals, stainless steel, rolled magnetic alloy materials and nickel copper alloys generally do not need protective layers;
(2) Carbon steel, low alloy steel and cast iron parts are easy to be corroded in the atmosphere, and passivation treatment is required after galvanizing and cadmium;
(3) Steel spring parts need to be dehydrogenated after galvanizing or cadmium plating;
(4) The products used in copper and its alloy parts and damp heat belts should be protected. Generally, the products can be treated with gloss pickling and passivation;
(5) Aluminum and aluminum alloy parts are sealed with dichromate after anodizing;
(6) Zinc alloy parts adopt phosphating, passivation and electroplating.
2. Select according to the purpose of coating
(1) Protective coating: the main function is to protect the base metal from corrosion, and the decorative requirements for products are not specified.
(2) Protective decorative coating: in addition to protecting the base metal, it also makes the parts beautiful.
(3) Functional coating: in addition to having a certain protective effect, it is mainly used for special work purposes.
