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Refined zinc cast into ingots or large blocks, the raw material of hot-dip galvanizing. More than half of the world's zinc is used to coat steel against corrosion — in batch galvanizing of fabricated steel and on continuous lines making galvanized and zinc-alloy-coated sheet — so zinc is the second metal every galvanizer and coil coater buys.
Zinc is produced mostly by roasting zinc sulphide concentrate, leaching it and electrowinning the metal, which gives zinc of 99.995% purity — special high grade (SHG), the grade the London Metal Exchange trades and the one galvanizers normally buy. Lower grades with more lead and cadmium, such as Prime Western, come from older smelting routes and secondary production.
In batch (general) galvanizing, fabricated steel — structural steel, pipe, gratings, fasteners — is cleaned, pickled and fluxed, and dipped in a kettle of molten zinc at about 445–460 °C. The zinc reacts with the steel to form iron-zinc alloy layers topped with pure zinc, a coating that protects by barrier and by sacrificial action. Small additions — nickel to control the reaction with silicon-bearing steels, aluminium, bismuth or tin for fluidity and brightness — are added as master alloys.
Continuous galvanizing lines coat steel strip by running it through a zinc pot containing about 0.2% aluminium, which suppresses the brittle iron-zinc layer; the pot is fed with jumbo blocks or pre-alloyed zinc-aluminium ingots. Zinc-aluminium and zinc-aluminium-magnesium coatings are made the same way with higher alloy additions.
The GCC has many batch galvanizing plants serving construction, power transmission, oil and gas and infrastructure, and several continuous galvanizing and coil-coating lines in the UAE, Saudi Arabia and Oman. The region has no zinc smelting of its own, so zinc is imported, priced off the LME with a regional premium. Galvanizing to ISO 1461 or ASTM A123 is the usual specification.
| Region | Standard | What it covers |
|---|---|---|
| International | ISO 752 ISO |
Zinc ingots — classification, chemical composition and marking of primary zinc |
| Europe | EN 1179 CEN-CENELEC |
Zinc and zinc alloys — primary zinc, grades Z1 (99.995%) to Z5 |
| USA | ASTM B6 ASTM |
Zinc — grades from LME grade and special high grade down to Prime Western |
| Japan | JIS H2107 JSA |
Zinc ingots |
| China | GB/T 470 SAC |
Zinc ingots — Zn99.995 and lower grades |
| International | ISO 1461 ISO |
Hot-dip galvanized coatings on fabricated iron and steel articles — specifications and test methods |
| USA | ASTM A123/A123M ASTM |
Zinc (hot-dip galvanized) coatings on iron and steel products |
| USA | ASTM A153/A153M ASTM |
Zinc coating (hot-dip) on iron and steel hardware |
Grade equivalents and the standards bodies: Steel grades & standards
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