galvanised

Galvanised refers to metal, typically iron or steel, that has been coated with zinc to protect it from corrosion. The process, galvanizing, creates a protective layer that can function as both a barrier to moisture and oxygen and as a sacrificial anode, slowing rust on the underlying metal.

The most common method is hot-dip galvanizing, in which cleaned steel parts are immersed in molten zinc. A metallurgical bond forms between zinc and iron, resulting in several iron-zinc intermetallic layers beneath a surface zinc coating. Electrogalvanizing, or electroplating, deposits zinc from an electrolytic bath to produce a thinner, more uniform coating, often used for complex shapes or smaller parts. Zinc spraying, including thermal or cold spray techniques, provides another coating option for touch-ups or large areas where dipping is impractical.

Protection from corrosion arises from two mechanisms. The zinc layer acts as a barrier to moisture and air, delaying rust. If the coating is damaged and the bare metal is exposed, zinc continues to corrode preferentially, protecting the steel through galvanic action. The effectiveness depends on coating thickness, environment, substrate quality, and mechanical integrity.

Standards and applications: Galvanized coatings are specified and assessed under standards such as ISO 1461 and ASTM A123/A123M. Coating thickness and durability vary with product type and service environment. Galvanized steel is widely used in construction (beams, pipes, fasteners), infrastructure, agricultural equipment, and outdoor hardware due to its extended service life and relatively low maintenance.

Maintenance and limitations: While durable, galvanized coatings can be damaged by impact, abrasion, bending, or harsh chemicals. Damaged areas may require repair through retinishing, re-galvanizing, or the application of zinc-rich coatings. The long-term performance depends on proper design, coating thickness, and exposure conditions.