Galvanized steel strip that is reheated immediately after leaving the zinc bath, so that iron from the steel diffuses into the coating and turns it into a zinc-iron alloy of about 10 % iron. The matt grey coating is harder, paints better and spot-welds more easily than pure zinc, which makes galvannealed (GA) sheet a standard material for car bodies and appliances.
Galvannealing is done on the same continuous line as ordinary galvanizing. After the air knives set the coating mass, the strip passes through an induction or gas-fired furnace at around 500–550 °C for a few seconds. Iron diffuses from the steel into the zinc and the coating converts completely into zinc-iron phases with about 8–12 % iron; the spangle disappears and the surface becomes an even, slightly rough matt grey.
The alloyed coating has three advantages over pure zinc. Paint and phosphate adhere to it very well, with no pre-treatment beyond cleaning, and painted GA resists blistering at scratches. It spot-welds with longer electrode life, because the iron-rich surface does not alloy with copper electrodes as readily as zinc. And it is harder and more resistant to scuffing in the press. The price is that the coating is somewhat more brittle — it can powder off in severe drawing, so coating masses are kept moderate — and unpainted it offers a little less sacrificial protection than the same mass of pure zinc.
Coatings are lighter than on building-grade GI: ZF100 or ZF120 in EN 10346 (100–120 g/m² total, about 7–8 µm per side), A40 or A60 in ASTM A653 (0.40 and 0.60 oz/ft²). GA is almost always painted in service.
Most galvannealed sheet goes to car and appliance makers under their own specifications, and in the Middle East it is a niche product supplied mainly by Japanese, Korean, Chinese and European mills for appliance, switchgear and door manufacturers.
Galvannealed is ordered like GI — base thickness × width, steel grade, coating class and surface — but with a ZF (EN) or A (ASTM) coating designation.
| Region | Standard | What it covers |
|---|---|---|
| Europe | EN 10346 CEN-CENELEC |
Continuously hot-dip coated steel flat products — zinc-iron alloy coating designated +ZF (ZF100, ZF120) |
| Europe | EN 10143 CEN-CENELEC |
Tolerances on dimensions and shape of continuously hot-dip coated sheet and strip |
| USA | ASTM A653/A653M ASTM |
Hot-dip zinc-coated (galvanized) or zinc-iron alloy-coated (galvannealed) steel sheet — coatings A01 to A60 |
| USA | ASTM A924/A924M ASTM |
General requirements for hot-dip metallic-coated steel sheet |
| Japan | JIS G3302 JSA |
Hot-dip zinc-coated steel sheets and strip, including alloyed (galvannealed) coatings |
| International | ISO 3575 ISO |
Continuous hot-dip zinc-coated and zinc-iron alloy-coated carbon steel sheet |
Grade equivalents and the standards bodies: Steel grades & standards
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