Exploration Of Corrosion And Corrosion Resistance Of Metallic Materials

Corrosion is the process of loss and destruction of materials (including metallic and non-metallic materials) under the action of the surrounding medium (water, air, acids, alkalis, salts, solvents, etc.). The corrosion resistance of metallic materials, that is, their ability to resist the erosion of the medium, is determined by the composition, chemical properties, organization and morphology of the material.
First, the classification of corrosion resistance of metal materials
Corrosion resistance of metal materials can be divided into the following categories according to its corrosion form:
1. chemical corrosion: the result of direct chemical interaction between the metal and the surrounding medium, including gas corrosion and metal corrosion in non-electrolyte. It is characterized by the corrosion process does not produce current, corrosion products deposited on the metal surface.
2. electrochemical corrosion: metal and electrolyte solution contact corrosion. Characterized by the corrosion process in the current generation, corrosion products do not cover the anode metal surface, but in a certain distance from the formation.
3. general corrosion: uniformly occurring on the internal and external surfaces of the metal, so that the cross-section is reduced, and ultimately damage to the stressed parts.
4. intergranular corrosion: in the metal along the edge of the grain, does not cause changes in the shape of the metal, but may lead to sudden destruction of equipment or machine parts.

5. point corrosion: concentrated in a small area of the metal surface, and quickly to the depth of the development, penetrate the metal, the harm is greater.
6. stress corrosion: under the action of static stress, the metal in the corrosive medium caused by the damage, usually through the grain.
Second, improve the corrosion resistance of metals
1. Alloying: steel with chromium, nickel, aluminum, titanium and other elements, can form a protective film to improve corrosion resistance.
2. electrochemical protection: by applying electric current or potential, change the electrochemical state of the metal, so that it is not easy to corrode.
Corrosion resistance test method
Corrosion resistance testing is an important means of assessing the durability of materials. Common test methods include:
1. salt spray test: simulate the corrosive environment in the atmosphere, to assess the corrosion resistance of materials.
2. Moist heat test: simulate the ocean, tropical and other environmental conditions, to assess the corrosion resistance of materials.
3. cyclic corrosion test: simulation of chemical corrosion and physical corrosion environment, to assess the corrosion resistance of materials.
Corrosion resistance test standards
To ensure the accuracy and reliability of the test results, corrosion resistance testing should follow certain standards, such as ASTM G85, ASTM B-117, ISO 9227, GB/T 6461-2002 and so on. These standards stipulate the specific methods, conditions and rating criteria of the test, which provide a scientific basis for the evaluation of the corrosion resistance of metal materials.