I would like to know what the term "passivated" means related to metal finishing.

"passivated" to me, means a zinc surface has been treated with a hexavalent chrome compound. The purpose of the passivation is to increase the amount of time before corrosion of the zinc begins. Some examples of zinc surfaces would be zinc die cast parts, galvanized steel sheet stock, or electrogalvanized sheet stock.

Another definition of passivated implies the protective oxide layer on stainless steel has been restored or regenerated after the parts have been fabricated or welded.

'Passivated' essentially means 'de-activated'. It doesn't have just a single meaning as a surface finish, however. Two very common meanings refer to the treatment of stainless steel in nitric acid or other materials to make it less prone to rusting, and the application of a chromate conversion coating to zinc or cadmium plating.

But there are other meanings too. For example, nickel anodes can become passivated, which is a bad thing rather than a good thing, because the anodes won't dissolve into the plating solution and it will run out of nickel.

There is a good explanation of passivation in ASTM A967 [link by ed. to spec at TechStreet] .

Passivation of stainless steel is basically the removal of exogenous materials and iron from the surface, thereby "chromium enriching" the surface. This is followed by oxidation of the chromium to form a corrosion resistant layer of chrome oxide on the surface. There are various ways to do this, as explained and detailed in that .

As an example, you can take 316L stainless steel, which is 18% chromium, and by passivating the surface reach up to 90% chromium in the surface layer. This chromium oxide layer is much more resistant to corrosion than the original surface.