Classification of corrosion resistance of metals

Corrosion resistance: The ability of a metallic material to resist the corrosive action of surrounding media

Objective To study the corrosion resistance of zinc nickel alloy coating. Methods The plating process of zinc nickel alloy was optimized by orthogonal test, and the plating solution formula was obtained. The corrosion resistance of the optimized Zn-Ni alloy coating was evaluated by neutral salt spray test and compared with that of zinc plating and cadmium plating. The effects of main salt, complexing agent, p H value, current density and temperature on corrosion resistance of the coating were analyzed. Results The optimal formula was zinc oxide 6~14 g/L, nickel sulfate 20~30 g/L, sodium hydroxide 100~140 g/L, brightener 4~6 g/L, complexing agent 50~70 g/L. In the neutral salt spray test, the time of white rust on the zn-Ni alloy coating obtained by this formula can reach more than 720 h. Conclusion The corrosion resistance of zinc-Ni alloy coating is better than that of zinc and cadmium plating.

Chemical corrosion is the result of direct chemical interaction between metal and surrounding medium. It includes two forms of gas corrosion and metal corrosion in non-electrolyte. Its characteristics are: the corrosion process does not produce current; And the corrosion products are deposited on the metal surface.

The corrosion caused by the interaction between metals and acid, alkali, salt and other electrolyte solutions is called electrochemical corrosion. It is characterized by an electric current generated during the corrosion process, and the corrosion product (rust) is not covered on the metal surface as the anode, but at a certain distance from the anode metal

General corrosion: This kind of corrosion is evenly enacted on the entire metal inside and outside the surface, so that the section is constantly reduced, and finally make the stressed parts destroyed

Intergranular corrosion: This type of corrosion occurs inside the metal along the grain edge, usually without causing any change in the shape of the metal, often resulting in sudden destruction of equipment or parts.

Point corrosion: This kind of corrosion is concentrated in a small area of the metal surface, and develops rapidly to the deep, and finally penetrates the metal. It is a kind of corrosion failure with greater harm

Stress corrosion: refers to the failure of a metal in a corrosive medium under static stress (the internal and external stress of the metal). This corrosion generally passes through the grain, that is, transgranular corrosion

Corrosion fatigue: refers to the failure of metals in corrosive media under alternating stress. It is also a transgranular corrosion

A common surface treatment for steel, especially sheet metal: When chromium is added, the surface will be bright, avoid hexavalent chromium, which is generally used as the coating of exposed metal parts, which is very beautiful. When nickel is added, corrosion prevention, and used with chromium, zinc is generally expressed by percentage. There are Fe//Zn8 zinc coating, and there are Fe//ZnFe(2)8 zinc iron coating. Relatively cheap, and good corrosion resistance coating, defects are easy to fall off after wear. Black, in black liquid soaking, this method is the simplest, the cheapest, the worst anti-corrosion effect, Dacroc1, expensive, complex process, corrosion resistance is very good, Delta seal(+Delta Tone), expensive, complex process, corrosion resistance is very good, often used in the domestic Dacroc1 substitute, if the requirements are reduced, more galvanized.