How does aluminum plate corrosion happen?

Corrosion has always been the primary factor affecting the service life of aluminum sheets. Although the aluminum plate treated by a certain process can be used in a complex environment, due to many factors that cause the corrosion of the aluminum plate, no perfect processing process can guarantee that the aluminum plate will not corrode. There are three main reasons for the corrosion of aluminum plates: environmental factors, metallurgical factors and stress factors, all of which affect each other.

1. Environmental factors

The environmental factors affecting the stress corrosion of aluminum plate mainly include: ion species, ion concentration, pH value of solution, oxygen and other gases, corrosion inhibitors, environmental temperature, environmental pressure, etc.

The stress corrosion of 2A12 and 7A04 aluminum plates in different atmospheric environments was studied, and it was found that aluminum plates had different stress corrosion susceptibility in different environments, and were more sensitive in marine environment. The marine environment contains a lot of salt, and Cl- will pass through the protective film on the surface of the aluminum plate and enter the interior, causing it to corrode.

Experiments show that when the mass concentration of HNO3 solution is between 20% and 40%, the corrosion of aluminum plate is intensified, and the corrosion rate of aluminum plate reaches the highest point when the concentration is about 35%. In the concentrated HNO3 solution, the stress corrosion of the aluminum plate is not obvious. The reason for this phenomenon is that a dense oxide film is formed on the surface of the aluminum plate, which prevents the further corrosion of HNO3.

2. Metallurgical factors

Metallurgical factors mainly include casting method, processing method and the influence of stress corrosion of gold in hot place. It is found that cathodic polarization increases the stress corrosion sensitivity of aluminum plate, and the stress corrosion sensitivity of friction stir welding is lower than that of fusion welding.

It is generally believed that properly treated 6061-T6 and 3004 aluminum sheets will not corrode. The difference of metallurgical factors changes the type of the outer film of the aluminum plate, and causes the difference of the internal structure of the aluminum plate and the change of the crystal structure, which affects the electrochemical behavior and mechanical behavior of the aluminum plate, resulting in different stress corrosion susceptibility of the aluminum plate.

3. Stress factor

The stress factors mainly include load type, load size, loading direction, loading speed and so on. For corrosion, the stress direction must be perpendicular to the grain boundaries in order to be able to separate them. One of the key factors for stress corrosion to occur is stress. Different stress effects will produce different effects. Corrosion fatigue caused by the combined action of alternating stress and environment is usually significantly different from stress corrosion cracking caused by fixed stress. Corrosion fatigue is usually more serious than stress corrosion. In addition, the difference of loading speed will also affect the susceptibility of aluminum plate to stress corrosion.

The above three factors often affect each other. Even if the simple treatment process can make the aluminum plate not affected by the corrosion of one environment, it is difficult to avoid the corrosion of the other two environments. Therefore, it is necessary to consider the use environment of the aluminum plate and do a good job of anti-corrosion.