Galvanic (electrolytic) galvanizing belongs to one of the most widespread (dominant) surface treatments and accounts for more than 68% of the world average. Zinc and zinc alloys are mostly used as a coating metal that protects the base material - steel - against corrosion. Zinc, in contact with iron, behaves like an anode and is preferably dissolved and covered with an oxide layer which retards further corrosion. Zinc coatings are not so decisive porosity. The influence of different atmospheric environments has a different effect on zinc coatings.
The usual outdoor atmosphere is zinc attacked slightly, but industrial exhales or, seawater greatly corrodes it. The quality of the input material fundamentally affects the final appearance of the plated piece. Coarse, corroded and heat - treated surfaces have reduced gloss and rough surface after galvanizing. The clean and smooth surface of the parts has a zinc layer with glossy and smooth finish. To increase corrosion protection, zinc coatings are subsequently modifiend, e.g. chromating or sealing the surface (pores) by applying a varnish, where to corrosion resistance of the material increases several times.
The corrosion resistance of electrolytically zinc coatings is generally similar to the corrosion resistance of zinc and other zinc coatings. Zinc corrosion is affected by the time the surface is exposed to - ecpecially moisture and dirt. In the initial stage, zinc works dominantly as a sacrificial metal and protects mechanically damaged areas on the steel surface. The dominant feature of zinc coatings is therefore the corrosion protection of steel and cast iron. The coating layers are typically in the range of 5 - 20 microns for normal corrosive environments or higher.
Demanded thickness of the zinc depends upon operating condition and upon demanded length of the life coating, e.g. FeZn 5 recommends on arid internal coatings. With higher pretension must be specified larger thickness of zinc.
Example: electroplating EN 12329-Fe//Zn12//C/
Chromating of coatings of zinc, as a next operation at zinc coatings according to ISO 4520, delays rising of the corrosion basis at the coatings, which are using in the aggressive atmosphere. Chromating slows down rising of the white corrosion, which forms on zinc coatings in the specific articles.
|A||achromatic||transparent, achromatic, eventual small sea-bow|
|B||no dyed||transparent, small sea-bow|
Ecological chromate Ecotri is exchromating passivation of zinc with high anticorrosive protection. It is advisable on passivation coatings of zinc and alloy, which does not contain Cr6+ and fluoride.