galvanizing

Galvanizing is a process that applies a zinc coating to steel or iron to protect it from corrosion. The coating provides sacrificial protection, as zinc is more anodic than iron, and also forms a barrier against moisture and air. The most common method is hot-dip galvanizing; other approaches include electrogalvanizing, sherardizing, and zinc spraying.

Hot-dip galvanizing involves cleaning the steel surface and immersing it in molten zinc, typically around 450°C. The coating comprises zinc and iron alloy layers with an outer zinc layer, which gives long-term corrosion resistance and allows complex shapes to be coated. Coating thickness varies with design and geometry.

Electrogalvanizing deposits zinc electrochemically from an electrolyte solution to produce thinner, more uniform coatings. This method is often used on sheet metal and components requiring tight tolerances or smooth surfaces, such as appliances, automotive parts, and enclosed assemblies. The protection is effective but generally shorter in life than hot-dip coatings in harsh outdoor environments.

Sherardizing coats by zinc diffusion in a rotating drum with zinc dust, and thermal spraying or metallizing apply zinc by flame or arc spraying, producing zinc-rich coatings on metal surfaces. These methods are chosen for specific applications, geometry, or post-treatment requirements.

Standards such as ISO 1461 and ASTM A123 specify coating thicknesses, adhesion, and testing methods for galvanized coatings. Galvanized coatings offer long service life, even in harsh climates, and can be repaired by recoating or touch-up. However, abrasion, chipping, or prolonged exposure to high temperatures may reduce effectiveness.

Common applications include infrastructure (bridges, culverts, guardrails), construction hardware, pipes, fasteners, automotive components, and agricultural equipment. In many markets galvanizing is favored for its cost-effectiveness and durability compared with paints or platings.