Which metal surface treatment is used to remove impurities such as rust, stains, inorganic contaminants, and scale from ferrous metals, copper, precious metals, and aluminum alloys?

• A. Passivation
• B. Pickling
• C. Galvanizing
• D. Anodizing

Answer: (B)

Pickling uses acidic solutions to dissolve oxide scales and contaminants from metal surfaces, making it ideal for cleaning ferrous metals, copper, precious metals, and aluminum alloys. The acid bath chemically removes rust, stains, inorganic contaminants, and oxide layers, leaving a clean surface ready for subsequent finishing steps like plating or coating. After pickling, parts are thoroughly rinsed and often passivated or otherwise finished. In contrast, passivation aims to form a protective oxide layer, galvanizing applies a zinc coating, and anodizing thickens or creates specific oxide layers (not cleaning) on aluminum.