Oxide Layer
The oxide layer is a thin layer on the surface of metals composed of metal and oxygen. It protects the material from further corrosion.
Physico-chemical mechanism
Oxide layers form via a chemical reaction between the metal and the air, where oxygen binds to the metal surface. This process is usually spontaneous and creates a stable layer that blocks further reactions with oxygen.
Metallurgical relevance & welding risks
The oxide layer has both pros and cons. It protects the metal from corrosion and increases strength, but it can also hurt weldability. A thin oxide layer can be easily removed by mechanical polishing or chemical cleaning. A heavy oxide layer, though, can be tough to get off and leads to poor welds if not fully removed.
Workshop practice & procedures
Before welding metal, thoroughly remove the oxide layer. You can do this with mechanical polishing (e.g., using a grinder) or chemical cleaners. For stubborn scale, it's a good idea to dip the metal in a liquid deoxidizer before welding. Follow the temperature and time specs for deoxidizing closely to get a sound weld.