The main factors that affect the stress corrosion of aluminum alloy

[China Aluminum Industry Network] Three conditions are required for metal materials to generate SCC: (1) materials sensitive to SCC; (2) service in specific corrosive environments (for aluminum alloys, in brine media or corrosive atmospheres); (3) Tensile stress. The main factors influencing the stress corrosion of aluminum alloys are environmental factors, metallurgical factors and stress factors. The three are interrelated and interact with each other.

1, environmental factors

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

After studying the stress corrosion of 2A12 and 7A04 aluminum alloys in different atmospheric environments, it was found that aluminum alloys have different stress corrosion sensitivities in different environments and are more sensitive in the marine environment. Marine environments contain large amounts of salt and Cl- The protective film passing 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 the aluminum alloy is intensified, and the corrosion rate of the aluminum alloy reaches a higher point when the concentration is about 35%. In the concentrated HNO3 solution, the aluminum alloy The stress corrosion is not obvious. The reason for this phenomenon is due to the formation of a dense oxide film on the aluminum alloy surface, which prevents further corrosion of HNO3.

2, metallurgical factors

The metallurgical factors mainly include the casting method, processing method and the effect of thermal stress corrosion on the hot metal. Cathodic polarization is found to increase the stress corrosion susceptibility of aluminum alloys. The stress corrosion sensitivity of friction stir welding is lower than that of fusion welding.

It is generally believed that the 6061-T6 and 3004 aluminum alloys that are properly treated will not exhibit SCC. The metallurgical factors will change the type of the aluminum alloy surface film, and cause the difference in the internal structure of the aluminum alloy and the change in the crystal structure, which affects the aluminum alloy. The electrochemical behavior and mechanical behavior of the aluminum alloy lead to different susceptibility to stress corrosion of the aluminum alloy.

3, stress factors

Stress factors mainly include load type, load size, loading direction, loading speed, etc. For SCC, the stress direction must be perpendicular to the grain boundary in order to be able to separate it. One of the key factors to generate stress corrosion is to have stress effect. Different stress effects produce different effects. Alternating stress and environmental interactions produce corrosion fatigue, which is usually significantly different from stress corrosion cracking caused by fixed stress. Generally, corrosion fatigue is more severe than stress corrosion. , Different loading speed will also affect the sensitivity of aluminum alloy stress corrosion.

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