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CORROSION RESISTANCE.

Commonly used metals are subject to varying levels of oxidation and deterioration (at times serious) if simply exposed to air. This occurs particularly intensely in hot and humid areas or in the vicinity of large industrial centres or sea resorts, where the air has a greater concentration of aggressive gases (sulphur dioxide, carbon dioxide, halogens), which may become hazardous to the integrity of the metal.
This corrosion is obviously accelerated when the metal parts, even if coated, come into contact with various chemical solutions or agents, in particular nitric acid and chloride solutions.
The table below states the guideline values of resistance to corrosion by Neutral Saline Mist on galvanic coated metals:

Base material
Coating
Chromium Chemical nickel Zinc
Iron/steel (polished)
20 micron
10 hours
20 micron
50 hours
5 micron
20 hours
(start of white corrosion)
Aluminium (99,5%)
20 micron
40 hours
 

Resistance to corrosion is significantly influenced both by the base material (in the case of aluminium the values can differ greatly depending on the type of alloy) and any post treatments applied after galvanic coating.
The dehydrogenisation treatment, required to limit fragility of the coating and improve adherence, leads to a drastic reduction in the corrosion resistance values, above all in the case of chromium coatings (with thicknesses of 20 micron, resistance to saline mist is max. 2 hours).
Bettini can perform laboratory tests on resistance to neutral saline mist according to the standard: UNI 9227.
Bettini technicians are available to advise on the ideal coating to apply where both resistance to wear and resistance to corrosion are required.

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