Galvanised steel sheet and coil: grades, coatings and gauges
Galvanised steel sheet and coil is flat carbon steel with a continuously applied zinc coating, used for roofing, cladding, enclosures, ducting and the strip that cold-formed sections are rolled from. ULAMEX supplies galvanised sheet in the forming grades DX51D to DX56D and the structural grades S250GD to S550GD, in zinc (Z) and zinc-magnesium (ZM) coatings, to EN 10346. This guide covers the grades, coatings, gauges, standards and uses. For the coating process and corrosion detail see our guide to galvanised steel and DX51D.
What galvanised sheet is
Galvanised sheet is cold-rolled steel strip passed continuously through a molten zinc bath, so both faces leave the line with a metallurgically bonded zinc coating. It is the flat product behind galvanised construction: roofing and wall sheet, enclosures, cabinets, ducting, rainwater goods and the coil that purlins, studs and profiles are cold-formed from. The zinc protects the steel two ways, as a barrier and sacrificially, so a scratch or a sheared edge does not rust the way bare steel does. The grade sets how far the sheet can be formed, and the coating class sets how long it lasts.
Forming and structural grades
EN 10346 splits galvanised sheet into two families: soft forming grades and higher-strength structural grades.
| Grade | Character and use |
|---|---|
| DX51D | General forming, the standard galvanised sheet grade, bending and shallow forming |
| DX52D | Medium forming, deeper bends |
| DX53D | Drawing quality, stamping and deep drawing |
| DX54D / DX56D | Extra deep drawing for complex pressed parts |
| S250GD to S550GD | Structural grades, the number is the minimum yield in MPa, for purlins, studs and load-bearing sections |
DX51D is the everyday galvanised sheet for general fabrication, DX53D and above for pressed and drawn parts, and the S grades for cold-formed structural sections where strength matters. State the grade with an enquiry so the sheet suits the forming and the load.
Zinc and zinc-magnesium coatings
The coating type and weight set the corrosion life, and both are chosen for the environment.
| Coating | Character |
|---|---|
| Z (zinc) | Standard hot-dip zinc, designated by weight both sides: Z100 to Z600 g/m2 |
| ZM (zinc-magnesium) | Magnelis and similar, more corrosion resistance for the same weight, strong cut-edge protection |
| AZ (aluminium-zinc) | Aluzinc, high barrier resistance and heat reflectivity |
The Z number is the total zinc weight in grams per square metre across both faces: Z100 suits dry indoor use, Z275 is the general outdoor default, and Z450 or Z600 suit coastal and industrial exposure. Zinc-magnesium coatings reach the same life at a lower weight and protect sheared edges better, which is why they suit demanding outdoor work. For the corrosion categories C2 to C5 and how coating weight maps to service life, see the galvanised steel guide.
Gauges and formats
Galvanised sheet is supplied as flat sheet and as coil for continuous processing. Sheet covers the common gauges for fabrication and roofing, and coil feeds roll-forming and slitting lines. The sheet is specified by grade, coating class, thickness and format, and the coating is included in the ordered thickness. State the grade, coating class, thickness and sheet or coil format with an enquiry for an accurate quotation.
Standards
Galvanised sheet and coil are supplied to EN 10346, the standard for continuously hot-dip coated flat steel products, which sets the grades, the coating classes and the delivery conditions.
| Standard | Scope |
|---|---|
| EN 10346 | Continuously hot-dip coated flat steel: forming and structural grades, Z, ZM and AZ coatings |
| EN 1090-1 EXC2 | Execution of steel structures, held by ULAMEX with welding to ISO 3834-2 |
A galvanising certificate stating the coating class and a 3.1 inspection certificate are supplied on request, so the sheet is documented against the specification.
Applications
Galvanised sheet serves construction and general fabrication. Roofing and wall cladding use profiled sheet in DX51D and the S grades. Enclosures, cabinets, cases and machine housings use flat sheet for a corrosion-resistant, paint-ready surface. Ducting, trays and rainwater goods use lighter gauges. Studs, tracks, purlins and light structural sections are cold-formed from structural-grade coil. Automotive and appliance work uses the deep-drawing grades for pressed panels. In each case the zinc coating removes the need to paint the steel just to stop it rusting.
Forming and welding galvanised sheet
Galvanised sheet bends, folds, roll-forms and presses like uncoated steel, with the grade chosen for the severity of the forming, and the zinc stays bonded through normal forming. It welds by MIG, spot and resistance welding, though the zinc burns back at the weld and gives off fume, so ventilation is used and the bare weld zone is re-protected with a zinc-rich paint. Drilled and sheared edges are protected by the sacrificial action of the zinc, which throws protection a short distance over the exposed steel, so a small cut edge does not rust. For heavy fabrication a zinc-rich repair coating restores continuous protection.
Painting and duplex systems
Galvanised sheet is often left as the bare zinc finish, but where colour or extra life is wanted it is painted or powder coated over the zinc, which is called a duplex system. The zinc and the coating protect synergistically, so a duplex system lasts longer than the two added separately. Fresh zinc is smooth and slightly reactive, so it is prepared first, by a sweep blast, a mordant wash or a suitable primer, so the paint bonds. Pre-painted coil, coated in the coil-coating line, is also available where a finished colour is needed straight from the sheet, which is common on roofing and cladding.
Storage and white rust
Newly galvanised sheet stored wet or tightly stacked without air can form a white powdery deposit, called white rust, where trapped moisture reacts with the fresh zinc. It is mostly cosmetic as a light bloom but consumes coating if it is heavy, so galvanised sheet and coil are stored dry, ventilated and off the ground, with spacers so air circulates between the sheets. Once the zinc has weathered and formed its stable grey patina it is far less prone to white rust. Light staining can be cleaned, but prevention by dry storage is better than removal.
Galvanised sheet versus alternatives
Galvanised sheet is the economical corrosion-resistant flat product for construction and enclosures. Against uncoated carbon sheet it needs no paint to survive outdoors; against stainless it is far cheaper where the mild corrosion resistance of zinc is enough; against aluminium it is heavier but stronger and cheaper. Where the environment is severe or the appearance is critical, a zinc-magnesium coating or a stainless sheet is specified instead. ULAMEX supplies galvanised alongside carbon, stainless and aluminium flat products, so a project sources the right one from a single supplier.
Galvanised steel sheet from ULAMEX
ULAMEX has supplied steel since 1988, and galvanised sheet is a core part of the range.
| What you get | Detail |
|---|---|
| Grades | Forming DX51D to DX56D, structural S250GD to S550GD |
| Coatings | Zinc Z100 to Z600, zinc-magnesium ZM, aluminium-zinc AZ |
| Forms | Flat sheet and coil |
| Standards | EN 10346; EN 1090-1 EXC2 with welding to ISO 3834-2 |
| Terms | 3.1 and galvanising certificate on request, no minimum order on stocked SKUs, dispatch 2 to 7 working days |
Need galvanised sheet or coil for a project? Send the grade, coating class, thickness and format, and ULAMEX will return a non-binding quotation. See our guides to galvanised steel and DX51D and structural steel grades, and our supply capabilities, or contact the export desk at [email protected] or +48 504 424 761.
Frequently asked questions
What grades is galvanised sheet available in?
Forming grades DX51D (general) to DX56D (extra deep drawing), and structural grades S250GD to S550GD where the number is the minimum yield in MPa. DX51D is the everyday galvanised sheet grade.
What does Z275 mean?
It is the zinc coating weight, 275 grams per square metre across both faces. Z100 suits dry indoor use, Z275 is the general outdoor default, and Z450 or Z600 suit coastal and industrial exposure.
What is the difference between Z and ZM coatings?
Z is standard hot-dip zinc. ZM is zinc-magnesium, such as Magnelis, which reaches the same corrosion life at a lower coating weight and protects sheared edges better, so it suits demanding outdoor work.
Can galvanised sheet be welded?
Yes, by MIG, spot and resistance welding. The zinc burns back at the weld and gives off fume, so ventilation is used and the weld zone is re-protected with a zinc-rich paint to restore continuous protection.
Do exposed edges rust?
Not readily. The zinc protects sheared and drilled edges sacrificially, throwing protection a short distance over the bare steel, so a small cut edge does not rust. Zinc-magnesium coatings give even stronger edge protection.
What standard applies to galvanised sheet?
EN 10346, for continuously hot-dip coated flat steel products, which sets the forming and structural grades and the Z, ZM and AZ coating classes. A galvanising certificate and a 3.1 certificate are supplied on request.
Can galvanised sheet be painted?
Yes. Painting or powder coating over the zinc gives a duplex system that lasts longer than either alone. The zinc is prepared first by a sweep blast, mordant wash or suitable primer so the coating bonds, and pre-painted coil is also available in a finished colour.
What is galvanised sheet used for?
Roofing and cladding, enclosures and cabinets, ducting and rainwater goods, pressed panels, and the coil that studs, tracks and purlins are cold-formed from. The zinc removes the need to paint the steel to stop it rusting.