On aluminum, alkaline etching leaves alloying elements such as copper, silicon and magnesium behind as a gray-black dusting; on steel, pickling can leave carbon smut. Smut wipes off on a white rag and ruins adhesion if powder goes over it. A deoxidizer or desmut stage, often acid-based, removes it before the conversion coating.
Heard on the job
Wipe test came back black on the 6061 extrusions, the desmut tank needs to be checked.
Also heard as
- etch smut
Related terms
Pretreatment
The cleaning and chemical conditioning a part gets before powder, which decides most of its adhesion and corrosion life.
Conversion coating
A thin layer formed by chemically reacting the metal surface, which improves adhesion and slows corrosion under powder.
Wash
Line slang for the spray pretreatment washer, or for the pass a part makes through it.