Let’s discuss methods to prevent corrosion fatigue

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Fracture caused by the combined effect of corrosion and alternating stress (stress direction changing periodically, also known as cyclic stress) is called corrosion fatigue. In the absence of corrosion, metals subjected to alternating stresses will experience fatigue failure. For ferroalloys, there is a critical value for the stress they can withstand; below this value, they will not suffer from fatigue fracture even after an infinite number of cycles. This value is known as the fatigue limit. Non-ferrous metals such as aluminum and magnesium do not have a fatigue limit, but their fatigue resistance also increases as the stress decreases. The critical stress value at which no fatigue fracture occurs over 10^6 cycles is typically defined as the fatigue limit. In a corrosive environment, the fatigue limit **decreases**, resulting in fatigue failure at lower stresses and shorter cycles. The morphological characteristics of corrosion fatigue are: numerous deep pits form; there can be multiple cracks that originate from the pits and propagate depthwise in a direction perpendicular to the stress. It is typically transgranular in nature, with branch cracks present, and the crack edges appear serrated. Corrosion fatigue occurs most easily in environments where pitting can take place; undoubtedly, the pits contribute to increasing stress. Cyclic stress causes the protective film to repeatedly rupture locally, exposing the bare metal at the cracks to continuous corrosion. Unlike stress corrosion, corrosion fatigue is not selective regarding the environment. Oxygen content, temperature, pH value, and solution composition all affect corrosion fatigue. Anodic polarization will promote corrosion fatigue. Prevention methods: Improve the design or perform heat treatment to eliminate and reduce tensile stresses. Shot peening of the surface generates compressive stresses. Electroplating with zinc, chromium, nickel, etc., can also be used; however, during electroplating, it is essential to ensure that no tensile stresses are generated in the plated layer and that no hydrogen penetration occurs. Corrosion inhibitors and cathodic protection can also be used.