Investigation On Corrosion And Corrosion Resistance Of Metal Materials

Investigation On Corrosion And Corrosion Resistance Of Metal Materials

Corrosion refers to the process of loss and destruction of materials (including metal materials and non-metallic materials) under the action of surrounding media (water, air, acid, alkali, salt, solvent, etc.). The corrosion resistance of metal materials, that is, their ability to resist medium erosion, is determined by the composition of the material, chemical properties, organizational morphology and so on.

1. Classification Of Corrosion Resistance Of Metal Materials

The corrosion resistance of metal materials can be divided into the following categories according to their corrosion form：

1) Chemical Corrosion: The result of direct chemical action between the metal and the surrounding medium, including gas corrosion and metal corrosion in non-electrolytes.It is characterized by the fact that no current is generated during the corrosion process, and the corrosion products are deposited on the metal surface;

2) Electrochemical Corrosion: Corrosion that occurs when a metal comes into contact with an electrolyte solution.The characteristic is that electricity is generated during the corrosion process, and the corrosion product does not cover the surface of the anode metal, but forms at a certain distance;

3) General Corrosion: It occurs evenly on the inner and outer surfaces of the metal, reducing the cross-section and ultimately destroying the stressed parts;

4) Intergranular Corrosion: It is carried out inside the metal along the edge of the grain, which does not cause changes in the shape of the metal, but may cause sudden damage to equipment or parts;

5) Pitting Corrosion: concentrated in a small area of the metal surface, and quickly develops to a deep depth, penetrating the metal, which is more harmful;

6) Stress Corrosion: Under the action of static stress, the damage caused by the metal in the corrosive medium usually passes through the grain.

2. Methods To Improve The Corrosion Resistance Of Metals

1) Alloying: Adding chromium(Cr), nickel(Ni), aluminum(Al), titanium(Ti) and other elements to steel can form a protective film and improve corrosion resistance;

2) Electrochemical protection: Through the application of current or potential, the electrochemical state of the metal is changed so that it is in a state that is not easy to corrode.

3. Corrosion Resistance Test Method

Corrosion resistance testing is an important means to evaluate the durability of materials.Common test methods include:

1) Salt spray test: Simulate the corrosive environment in the atmosphere and evaluate the corrosion resistance of the material;

2) Heat and humidity test: Simulate marine, tropical and other environmental conditions to evaluate the corrosion resistance of materials;

3) Cyclic corrosion test: Simulate chemical corrosion and physical corrosion environments to evaluate the corrosion resistance of materials.

4, Corrosion Resistance Test Standards

In order to ensure the accuracy and reliability of the test results, the corrosion resistance test should follow certain standards, such as ASTM G85, ASTM B-117, ISO 9227, GB/T 6461-2002, etc. These standards specify the specific methods, conditions and rating standards for testing, and provide a scientific basis for the evaluation of the corrosion resistance of metal materials.