There are three conditions for the production of SCC from metallic materials: (1) the material is sensitive to SCC; (2) it is used in a specific corrosive environment (for aluminum alloys, in a saline medium or corrosive atmosphere); (3) is subjected to tensile stress. . The factors affecting the stress corrosion of aluminum alloy mainly include environmental factors, metallurgical factors and stress factors. The three are connected and interact with each other.
1. Environmental factors
The environmental factors affecting the stress corrosion of aluminum alloy are: ion type, ion concentration, solution pH, oxygen and other gases, corrosion inhibitors, ambient temperature, environmental pressure, etc.
The stress corrosion of 2A12 and 7A04 aluminum alloys in different atmospheric environments was studied. It was found that aluminum alloys have different stress corrosion sensitivities in different environments and are sensitive in marine environment. The marine environment contains a large amount of salt, Cl- will The protective film that passes through the surface of the aluminum alloy enters the interior and corrodes it.
Experiments show that when the mass concentration of HNO3 solution is between 20% and 40%, the corrosion of aluminum alloy is intensified, and the corrosion rate of aluminum alloy reaches the highest point at a concentration of about 35%. In concentrated HNO3 solution, aluminum alloy Stress corrosion is not obvious. The reason for this phenomenon is that a dense oxide film is formed on the surface of the aluminum alloy, which prevents further corrosion of HNO3.
2, metallurgical factors
The metallurgical factors mainly include the casting method, processing method and the influence of gold stress corrosion at the hot point. It is found that the cathodic polarization makes the stress corrosion sensitivity of the aluminum alloy increase, and the stress corrosion sensitivity of the friction stir welding is lower than that of the fusion welding.
It is generally believed that the appropriately treated 6061-T6 and 3004 aluminum alloys do not exhibit SCC. The difference in metallurgical factors changes the type of aluminum alloy surface film, and causes the internal structure of the aluminum alloy to change and the crystal structure changes, thereby affecting the aluminum alloy. The electrochemical behavior and mechanical behavior lead to different stress corrosion susceptibility of aluminum alloys.
3, stress factors
Stress factors mainly include load type, load size, loading direction, loading speed, etc. In the case of SCC, the stress direction must be perpendicular to the grain boundary so as to be able to separate it. One of the key factors for stress corrosion is stress. Different stresses produce different effects. The alternating stress and the environment work together to produce corrosion fatigue, which is usually significantly different from the stress corrosion cracking caused by fixed stress. Usually corrosion fatigue is more serious than stress corrosion. The difference in loading speed also affects the sensitivity of aluminum alloy stress corrosion.
Keywords: 7075 aluminum alloy 7075 aluminum plate imported 7075 aluminum plate American Airlines metal