Corrosion of metals and rust-proof rust of metal parts

1. Cause of metal corrosion

Corrosion of metals has two types of chemical corrosion and electrochemical corrosion.

(1) Chemical corrosion

The phenomenon of chemical damage caused by metal materials and external media is called chemical corrosion. No current is generated during chemical etching, but it is a simple chemical action. For example, oxidation of a metal surface in a dry atmosphere at room temperature. For different metals, the structure and properties of the oxides are different, and some can form a fine and stable solid oxide film on the metal surface, so that the inner layer metal is isolated from the external medium and play a protective role, such as Chromium, aluminum, zinc, etc.; and some oxide layer is loose and easy to fall off, so that the inner layer of metal continues to be eroded by corrosive media, this metal corrosion speed is very fast, such as iron, magnesium, copper and so on. The oxidation rate of the metal is much faster at high temperatures than at low temperatures, and preventing the metal from contacting the highly oxidizing medium can slow or prevent the chemical corrosion of the metal. Common corrosion media include oxygen, hydrogen, carbon monoxide, carbon dioxide, hydrogen sulfide, hydrogen chloride, and industrial exhaust gases.

(2) Electrochemical corrosion

Corrosion caused by electric current during the corrosion process is called electrochemical corrosion.

Metals are more or less always contain certain impurities, different metals have different potentials, and different compositions in the same metal also have different potentials. When the metal is in contact with a certain electrically conductive solution, a potential difference occurs, causing electron flow in the solution, causing the metal with a low potential to be first etched.

Corrosion is not only determined by the chemical nature of the metal itself, but also has a lot to do with the surrounding media and the microstructure of the metal. If the wet environment is easier to rust than the dry environment, metals with less impurities are more likely to rust than metals with less impurities. Under high temperature conditions, corrosion is more likely to occur than under low temperature conditions. Dangerous and dirty environments are more likely to rust than air circulation and clean environments. Metal parts The surface finish is low and the surface finish is higher than that of the easy rust.

2. Rusted features of common metals

(l) Steel and cast iron

When it starts to rust, the surface is dark gray and gradually develops yellow-brown powdery rust, which develops into brown or brown scars.

(2) Copper and its alloys

Rusted features are brownish red or green layers. The main component of green rust produced on the surface of copper is basic copper carbonate; copper hydroxide is dark blue, cuprous oxide is red, and copper oxide is black.

(3) Aluminum and its alloys

Corrosion characteristics are white or dark gray spots, sometimes white powder appears in the corroded place, and then continue to develop, and rust pits filled with corroded products appear.

(4) Zinc Plating, Cadmium Plating, Tin Plating

Plating rust is characterized by gray, black spots or white powder thin layers.

(5) blue parts

The blue color itself is an artificial oxide layer protective film, and its corrosion characteristics are brown rust spots or rust spots, and sometimes have little difference with the blue color (purple brown, blue black, blue-brown).

(6) Phosphating Parts

Phosphate film corrosion features with steel parts. Others such as zinc and aluminum alloys have the same characteristics of corrosion as Zn and aluminum alloys themselves.

(7) Sandblasting parts

The original fine-grained sandblasted surface was grayish and rusted when corroded.

(8) Painted parts

When rust occurs under the paint layer, it will cause the lacquer layer to bulge and blistering so that it will explode and rust.

3. Anti-rust method for metal parts

Commonly used metal parts anti-rust methods are oxidation, phosphating, plating, spraying plastic coating, brush coating anti-rust coating method. The first few are generally used in the manufacturing process of parts. Only the anti-rust paint coating method is introduced.

(1) Various steel parts

Can be coated with anti-rust paint. First apply the red enamel anti-rust paint (primer) on the surface of the part, and then apply a layer of anti-rust paint (top coat). Note that the machined surface of the part cannot be painted.

(2) Bearings can be coated with petroleum jelly with 1% refined rosin.

(3) Spring springs must not be oiled. If rust marks are found, they can be removed with a soft brush and coated with graphite.

(4) Various bolts can be scrubbed with kerosene and then coated with a thin layer of neutral mineral waste motor oil.

(5) Various precision parts, tools, etc.

Can be coated with various anti-rust grease.

In the rust-proof work of metal parts, the method of brushing rust-proof grease is simple and practical. There are many varieties of finished rust-proof oils available on the market, common are anti-rust oils, rust-proof greases, rust-proof greases, vapor phase corrosion inhibitors, peelable plastics, etc., which can be based on different types of accessories and different protection requirements. Choose to use.