Corrosion is always the primary factor affecting the service life of aluminum plate. After a certain process although the aluminum plate can be used in a complex environment, but because of the corrosion caused by many factors, and the perfect process can not guarantee the aluminum plate will not be corrosion. There are three main reasons for the corrosion of Aluminum Plate: Environmental Factors, metallurgical factors and stress factors, which affect each other.
1. Environmental Factors
The main environmental factors affecting stress corrosion of aluminum sheet are ion type, ion concentration, pH value of solution, oxygen and other gases, corrosion inhibitor, ambient temperature, ambient pressure, etc. .
The stress corrosion behaviors of 2A12 and 7A04 aluminum plates in different atmosphere were studied. Cl-enters the ocean environment through a protective coating on the outer surfaces of aluminum plates, corroding them when they are high in salinity.
The results show that when the concentration of HNO3 solution is between 20% and 40% , the corrosion rate of aluminum sheet increases, and the corrosion rate reaches the highest when the concentration is about 35% . In concentrated HNO3 solution, the stress corrosion cracking of aluminum sheet is not obvious, because a dense oxide film is formed on the surface of aluminum sheet, which prevents further corrosion of HNO3.
2. Metallurgical Factors
It is found that CATHODIC polarization makes stress corrosion sensitivity of aluminum sheet increase, and friction stir welding is less sensitive to stress corrosion than fusion welding.
Properly treated 6061-T6 and 3004 aluminium sheets are generally considered to be free from corrosion. The different metallurgical factors change the type of the outer surface film of the Aluminum Plate, and cause the difference of the internal structure and the change of the crystal structure of the aluminum plate, thus affecting the electrochemical behavior and mechanical behavior of the Aluminum Plate, resulting in the difference of the stress corrosion susceptibility of aluminum plate.
Stress factors include load type, load size, load direction, load speed and so on. In the case of corrosion, the stress direction must be perpendicular to the grain boundary so that it can be separated. One of the key factors of stress corrosion is the stress effect. But different stress will produce different effect, the alternating stress and the environment work together to produce corrosion fatigue, and the stress corrosion cracking of the fixed stress often have obvious difference. Corrosion fatigue is usually more severe than stress corrosion. In addition, the different loading speed can also affect the sensitivity of stress corrosion of aluminum sheet.
The above three factors are often affected each other, a simple process even if the aluminum plate from the impact of one kind of environmental corrosion, it is difficult to avoid the other two kinds of environmental corrosion. Therefore, to consider the overall use of aluminum plate environment, do a good job in corrosion work.