Reasons for Corrosion of Embossed Aluminium Coil Rolls

Corrosion has ranked first among factors influencing service life of the embossed aluminum. After going through relative technological processes, embossed aluminium coil rolls go well in complex environments, but there are so many possible factors that no process is perfect enough to keep the rolls completely off corrosion. Generally speaking, there are three reasons for corrosion of embossed aluminium coil rolls: environment, metallurgy and stress.

The main environmental factors affecting stress corrosion of embossed aluminium coil rolls are ion species, ion concentration, solution pH value, oxygen and other gases, corrosion inhibitors, environmental temperature, environmental pressure and so on. After studying the stress corrosion of embossed aluminium sheets in different atmospheric environments, researchers found that the stress corrosion sensitivity varies in different environments and more sensitive in marine environments. For example, marine environment has lots of salt in the air. Cl element will enter the interior through the maintenance film on the exterior of embossed aluminium rolls and cause corrosion to it. Experiments show that when the mass concentration of HNO3 solution is between 20% and 40%, the corrosion is aggravated, and the corrosion rate reaches the highest point when the concentration is about 35%. In concentrated HNO3 solution, the stress corrosion is not obvious. The reason for this phenomenon is that a dense oxide film formed on the surface of the coil, which prevents the further corrosion of HNO3.

Metallurgical factors mainly include casting mode, processing mode and stress corrosion of hot spot gold. It is found that cathodic polarization increases the stress corrosion sensitivity of embossed aluminium coil rolls, and the stress corrosion sensitivity of friction stir welding is lower than that of fusion welding. It is generally believed that 6061-T6 and 3004 embossed aluminium sheet coil rolls treated properly will not be corroded. The different metallurgical factors change the type of outer film of the roll, and result in the changes of the roll’s internal structure and crystal structure, which affects the electro-chemical and mechanical behavior and leads to strengthened stress corrosion susceptibility.

Stress factors mainly include load type, load size, loading direction, loading speed and so on. As far as corrosion is concerned, 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 stress. Different stress effects will produce different effects. Alternating stress and environmental interaction will lead to corrosion fatigue, which is usually different from stress corrosion cracking under fixed stress. Corrosion fatigue is usually more serious than stress corrosion. In addition, the different loading speed also affects the susceptibility of stress corrosion of embossed aluminium sheet.

The three factors above, however, usually influence each other in practical processing periods. Simple treatment methods may spare embossed aluminium sheet coil rolls from one factor, but not from all of them.