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How does aluminum corrosion occur?
May 01, 2018

Corrosion has always been the primary factor affecting the service life of aluminum plates. Aluminum plates processed through certain processes can be used in complex environments. However, due to many factors that cause aluminum plate corrosion, perfect processing procedures cannot guarantee that aluminum plates will not corrode. There are three major causes of aluminum corrosion: environmental factors, metallurgical factors and stress factors, these three are mutually affecting.


1, environmental factors


The environmental factors that affect the stress corrosion of aluminum plates are: ion species, ion concentration, solution pH, oxygen and other gases, corrosion inhibitors, ambient temperature, and environmental pressure.


The stress corrosion of 2A12 and 7A04 aluminum plates in different atmospheric environments was studied. It was found that aluminum plates have different stress corrosion sensitivities in different environments and are more sensitive in the marine environment. The marine environment contains a lot of salt, Cl- will go through the maintenance film outside the aluminum plate into the interior, causing corrosion.


The experiments indicate that when the mass concentration of HNO3 solution is between 20% and 40%, the corrosion of the aluminum plate is intensified, and the corrosion rate of the 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 to prevent further corrosion of the HNO3.


2, metallurgical factors


The metallurgical factors mainly include the casting method, processing method and the effect of thermal stress corrosion of the metal. It is found that the cathodic polarization increases the stress corrosion sensitivity of the aluminum plate, and the friction corrosion sensitivity of the friction stir welding is lower than that of the fusion welding.


It is generally believed that 6061-T6 and 3004 aluminum plates that are properly treated will not corrode. The metallurgical factors have changed the type of the outer film of the aluminum sheet, and caused changes in the internal structure of the aluminum sheet and changes in the crystal structure, thereby affecting the electrochemical behavior and mechanical behavior of the aluminum sheet, resulting in different stress corrosion susceptibility of the aluminum sheet.


3, stress factors


Stress factors include load type, load size, loading direction, loading speed, and so on. In the case of corrosion, the direction of stress must be perpendicular to the grain boundary so that it can be separated. One of the key factors for stress corrosion is stress. Different stress effects will produce different effects. Corrosion fatigue occurs due to the interaction between alternating stress and the environment, and there is usually a clear difference between stress corrosion cracking and fixed stress. Corrosion fatigue is usually more severe than the result of stress corrosion. In addition, the difference in loading speed will also affect the sensitivity of aluminum stress corrosion.


The above three factors often influence each other. Even if the simple processing procedure can prevent the aluminum plate from being affected by an environmental corrosion, it is difficult to avoid the corrosion of the other two environments. Therefore, it is necessary to consider the use environment of aluminum plates and do a good job of anti-corrosion work.


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