Pretreatment, conversion coatings and passivation
Chemical bath processes before finishing: phosphating, passivation, pickling of weld discoloration and plating defects.
Basics
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Passivation method by stainless steel grade: 303, 304, 316, 400
300-series grades take plain nitric or citric passivation; 303 and martensitic 400-series grades need inhibited nitric or citric baths. See each family.
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What is zinc plating and how does it protect steel parts?
Zinc plating is an electroplated zinc layer that shields steel and corrodes first where steel is bare. See what passivate adds and which metals take it.
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What is a chemical conversion coating (chem film) on aluminum?
Chem film is a thin chromate or trivalent chromium layer formed on aluminum by immersion. It resists corrosion, holds paint and stays conductive.
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What is phosphate coating on steel and what is it used for?
Phosphate coating turns steel into iron, zinc or manganese phosphate crystals that anchor paint or hold oil. See how it forms and which type does what.
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What is stainless steel passivation and what does it do?
Passivation removes free iron from stainless steel so a chromium-rich passive film can form. See what it fixes, what it cannot remove and how to check it.
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Pickling vs passivation of stainless steel: what is different?
Pickling removes heat tint and scale by dissolving a metal layer; passivation only removes free iron. See which surface needs one treatment or both.
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Passivation vs electropolishing for stainless steel: which one?
Passivation removes free iron but no metal; electropolishing typically removes 5 to 10 µm to smooth stainless steel and strip heat tint. Which fits a part?
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Iron, zinc or manganese phosphate: which coating should you use?
Iron phosphate suits indoor painted steel, zinc phosphate suits outdoor or salt exposure and manganese suits sliding parts. See the choice by condition.
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Zinc plating vs hot-dip galvanizing: which coating to specify
Zinc plating suits small threaded parts in mild exposure; hot-dip galvanizing suits outdoor steel needing far more zinc. Compare thickness, threads, specs.
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How to choose an aluminum conversion coating: Cr6, Cr3 or none
Use hexavalent chromate only where a spec demands it, trivalent chromium for conductive or paint-base parts and zirconium films for painted parts.
Turn technical reasoning into better results.