Selective Diffusion Corrosion
Selective diffusion corrosion is a process where certain alloying elements are selectively leached out of the metal due to concentration gradients and grain boundary diffusion. This leads to localized corrosion susceptibility and can impair the strength and reliability of the material.
Physicochemical Mechanism of Action
Selective diffusion corrosion occurs when certain metals or alloys stand in a corrosive medium (like air, water or chemical liquids). The different alloying elements have different diffusion rates and solubilities in the corrosive medium. This leads to concentration gradients within the metal, where certain elements (often heavy metals like nickel or copper) are leached out faster than others.
Metallurgical Relevance & Welding Risks
Selective diffusion corrosion can lead to local corrosion susceptibility and cracks, especially at spots with high mechanical loads or with uneven cooling. This hurts the strength and reliability of the material, which can be dangerous in critical applications like mechanical engineering or aviation.
Workshop Practice & Instructions
To avoid selective diffusion corrosion, it is important:
• To ensure a correct weld and make sure there are no gaps or crevices.
• For metals with a high content of heavy alloying elements, to carry out careful cooling to minimize concentration gradients.
• To consider the use of corrosion-fighting protective agents and methods (like galvanizing or coating) in critical areas.