Galvanised Steel (DX51D)
Pre-galvanised DX51D+Z sheet for ducting, enclosures, brackets and trays: laser cutting, punching and bending
Galvanised steel is low-carbon steel sheet with a zinc coating applied at the mill (hot-dip, continuous line). The standard grade is DX51D+Z to EN 10346, supplied 0.5 to 3 mm thick with zinc mass Z100 to Z275 (100 to 275 g/m² on both faces together). It is the default material for HVAC ducting, electrical enclosures, cable trays, shelving and light brackets in Egypt, the UAE and Saudi Arabia because it resists rust without any post-coating and costs only slightly more than bare mild steel. Upload a DXF and receive a binding quote within 12 hours.
This page covers the grades and coating masses, what happens to the zinc at laser-cut and bent edges, thickness and tolerance limits, and how pre-galvanised sheet compares with hot-dip galvanising after fabrication.
Grades and coating designations
EN 10346 designates the steel by formability (DX51D basic, DX52D deep drawing, DX53D extra deep) and the coating by type and mass. +Z is pure zinc, +ZA zinc-aluminium (Galfan), +AZ aluminium-zinc (Galvalume-type, 55% Al). The number is total zinc mass on both sides in g/m²; divide by roughly 14 to get thickness per side in µm, so Z275 is about 20 µm per side.
Structural galvanised grades S250GD to S350GD+Z are used where strength is specified, for example solar purlins and rack uprights. Ask for the mill certificate if your project requires it; suppliers in the CutLinq network hold ISO 9001 and can attach EN 10204 3.1 certificates on request.
| Designation | Zinc mass (both sides) | Thickness per side | Typical use | Relative price vs DC01 bare |
|---|---|---|---|---|
| DX51D+Z100 | 100 g/m² | about 7 µm | indoor ducting, dry areas | 1.10 to 1.15 |
| DX51D+Z140 | 140 g/m² | about 10 µm | enclosures, shelving | 1.12 to 1.18 |
| DX51D+Z200 | 200 g/m² | about 14 µm | general fabrication, most stock in MENA | 1.15 to 1.20 |
| DX51D+Z275 | 275 g/m² | about 20 µm | outdoor, coastal, humid plant rooms | 1.18 to 1.25 |
| S350GD+Z275 | 275 g/m² | about 20 µm | solar purlins, rack uprights | 1.25 to 1.35 |
| DX51D+AZ150 | 150 g/m² Al-Zn | about 20 µm | roofing, high heat reflectivity | 1.20 to 1.30 |
Laser cutting and punching galvanised sheet
Fiber lasers cut DX51D+Z cleanly from 0.5 to 3 mm; the zinc vaporises at the kerf and the cut edge is bare steel about 0.2 mm wide with a thin zinc-rich zone from the melt. In dry indoor use the edge does not rust for years because the surrounding zinc protects it cathodically. In coastal Alexandria, Jeddah or Sharjah, or in washdown areas, edges thicker than 1.5 mm should be touched up with zinc-rich paint or the part should be powder coated.
CNC punching is common for enclosures and trays with hundreds of identical holes and louvres; the punch does not remove zinc from the sheet face, only the sheared edge is bare. Plasma is not recommended below 3 mm because of the wide kerf and zinc fume.
| Thickness | Laser tolerance | Min hole diameter (laser) | Min hole diameter (punch) | Notes |
|---|---|---|---|---|
| 0.5 to 0.8 mm | ±0.1 mm | 0.5 mm | 1.0 mm | ducting, cladding, light covers |
| 1.0 to 1.5 mm | ±0.1 mm | 0.8 mm | 1.5 mm | enclosures, trays, brackets |
| 2.0 mm | ±0.15 mm | 1.5 mm | 2.0 mm | structural brackets, mounting plates |
| 2.5 to 3.0 mm | ±0.2 mm | 2.5 mm | 3.0 mm | edge touch-up recommended outdoors |
Bending galvanised sheet
DX51D bends easily; a minimum inside radius equal to the sheet thickness is safe and 0.5 times thickness is possible on Z100 to Z200 without flaking. Zinc on the outside of the bend stretches but stays adherent at these radii. Angle tolerance is ±0.5° on a CNC press brake, with a flange length tolerance of ±0.3 mm for a single bend and ±0.5 mm across a box with four bends.
The zinc layer is softer than the steel, so V-die marks on the outside face are visible; specify film-protected sheet or urethane die pads if the part is a visible cover.
- Minimum flange length: 4 times thickness plus inside radius (a 1.5 mm sheet needs 7.5 mm flange for a 1.5 mm radius)
- Minimum inside bend radius: 1.0 t standard, 0.5 t on Z100 to Z200
- Angle tolerance: ±0.5°; flange length ±0.3 mm per bend
- Bend relief: 1.5 t wide, t deep at flange intersections to prevent tearing
- Hem and seam joints (Pittsburgh lock, snap lock) available for ducting up to 1.2 mm
Pre-galvanised versus hot-dip galvanising after fabrication
Pre-galvanised sheet arrives coated and is cut and bent afterwards; edges and welds are bare and the coating is 7 to 20 µm. Hot-dip galvanising after fabrication (EN ISO 1461) dips the finished part into molten zinc at 450 °C, coats every edge and weld, and gives 45 to 85 µm depending on thickness, but it costs more, adds 3 to 6 working days, and can warp thin parts. For sheet under 3 mm indoors, pre-galvanised is almost always the right choice; for welded frames outdoors in Saudi Arabia or on the UAE coast, fabricate in S235JR and hot-dip galvanise afterwards.
| Property | Pre-galvanised DX51D+Z275 | Hot-dip after fabrication (ISO 1461) | Zinc electroplating |
|---|---|---|---|
| Zinc thickness | about 20 µm per side | 45 to 85 µm | 5 to 12 µm |
| Edge and weld protection | bare, cathodic protection only | fully coated | fully coated (thin) |
| Expected life, C3 urban dry (Cairo, Riyadh) | 15 to 25 years | 40 years or more | 3 to 8 years |
| Expected life, C4 to C5 coastal (Alexandria, Dubai, Dammam) | 5 to 10 years | 15 to 25 years | 1 to 3 years |
| Distortion risk | none | moderate on thin sheet | none |
| Extra lead time | 0 days | 3 to 6 working days | 2 to 3 working days |
| Relative cost on a 2 mm bracket | 1.0 | 1.4 to 1.8 | 1.2 to 1.3 |
Welding and finishing galvanised parts
Galvanised sheet can be MIG or spot welded but the zinc burns off around the weld and produces fume; the joint must be cleaned and re-protected with zinc-rich paint or powder coating. Where possible use rivets, self-clinching nuts or Pittsburgh seams instead of welding. Powder coating over galvanised sheet needs a phosphate or chromate-free pretreatment and light sanding to avoid outgassing pinholes; specify 60 to 80 µm polyester for indoor and 80 to 120 µm for outdoor use.
Design tips
- Specify DX51D+Z200 for indoor and DX51D+Z275 for outdoor or coastal parts; write the designation on the drawing.
- Keep inside bend radius at 1.0 times thickness and flanges at least 4 t plus radius, so 1.2 mm sheet needs 6 mm flanges.
- Use 1.5 t wide bend reliefs at every flange intersection to prevent the zinc cracking at the corner.
- Prefer riveting or self-clinching fasteners over welding; every weld on galvanised sheet needs post-cleaning and touch-up.
- Order 1.0 mm instead of 0.8 mm for enclosure doors over 600 mm wide to avoid oil-canning.
- For hole patterns over 200 holes per part, request CNC punching rather than laser; it is faster on 0.8 to 2 mm sheet.
- Outdoors in the Gulf, either add powder coating or switch to hot-dip galvanising after fabrication for parts over 2 mm.
Applications
| Industry | Example parts | Typical material |
|---|---|---|
| HVAC and ducting | rectangular duct, plenums, dampers, flanges | DX51D+Z140 to Z275, 0.5 to 1.2 mm |
| Electrical enclosures | panel boxes, gland plates, cable trays | DX51D+Z200, 1.0 to 2.0 mm |
| Solar mounting | purlins, clamps, rail brackets | S350GD+Z275, 1.5 to 3 mm |
| Construction | stud framing, lintels, angle cleats | DX51D+Z275, 1.0 to 2.0 mm |
| Furniture and retail | shelving, racking, lockers | DX51D+Z140, 0.8 to 1.5 mm |
| Agriculture | feeder troughs, greenhouse brackets | DX51D+Z275, 1.5 to 2.5 mm |
| Machinery guards | covers, chip trays, brackets | DX51D+Z200, 1.5 to 3 mm |
Pricing and lead time
Galvanised part price is driven by three factors: sheet thickness and coating mass (Z275 costs 5 to 8% more than Z100 and 2 mm costs roughly twice as much material as 1 mm), cutting length and hole count (a duct flange with 40 holes takes three times longer to cut than a plain blank), and the number of bends. A 300 x 200 mm DX51D+Z200 bracket, 1.5 mm, with four holes and two bends serves as a reference of 1.0; the same part in 1.4301 (304) stainless costs about 2.5 to 3.0, and in bare DC01 with powder coating about 1.3 to 1.5. Lead time for cut and bent galvanised parts is 2 to 4 working days; add 3 to 5 working days for powder coating. Small parts ship by courier next day within Cairo, 6th of October, Dubai, Sharjah, Riyadh and Dammam; pallets arrive in 1 to 2 days, and WhatsApp support confirms dispatch.
Frequently asked questions
Indoors in dry conditions, no; the surrounding zinc protects the narrow bare edge. Outdoors, in humid plant rooms or near the coast, edges on sheet over 1.5 mm should be touched up with zinc-rich paint or the part powder coated.
Upload your DXF or STEP file for galvanised steel parts and receive a binding quote within 12 hours.