Beyond soldering, lead-tin alloys find application as protective coatings, particularly for steel, where they provide a combination of corrosion resistance, solderability, and lubricity. These coatings are applied by hot-dipping (similar to galvanizing) or electroplating. The most common coating alloy is terneplate, which historically contained 10-25% tin with the balance lead, though modern versions often use lead-free alternatives. Terne-coated steel offers excellent resistance to atmospheric corrosion, especially in roofing and automotive fuel tank applications.
The corrosion resistance stems from the formation of stable, adherent oxide films on both lead and tin. Tin provides a more protective, passive layer, while lead offers sacrificial protection in some environments. In acidic or alkaline conditions, the behavior can be complex; generally, higher tin content improves resistance to many industrial chemicals and soft waters. A key advantage of lead-tin coatings over pure zinc (galvanizing) is their ability to be easily soldered, which was crucial for fabricating fuel tanks and other sealed assemblies.
Mechanically, these coatings are soft and malleable, allowing the coated steel to be formed, drawn, or stamped without flaking or cracking. They also provide good dry lubricity during metal-forming operations. However, their softness makes them susceptible to abrasion. The use of lead in such coatings has declined due to environmental and health regulations, with alternatives like tin-zinc or purely tin coatings being developed. Nevertheless, for specific historical restoration projects or in certain industrial contexts where its unique properties are irreplaceable, lead-tin coatings remain in limited use.
