1. What Is DX51D Galvanized Steel?
DX51D is the most widely specified hot-dip galvanized steel grade in the EN 10346 system (steel number 1.0917). In the designation, "D" marks a flat product intended for cold forming, "X" means the composition is not fixed but adjusted to achieve the guaranteed properties, and "51" identifies the base forming tier - general forming, bending and simple stamping. The "+Z" suffix indicates the hot-dip zinc coating. DX51D is the default material for a huge range of products: roofing and cladding profiles, cable trays, enclosures, ductwork, furniture parts, and any component that needs good formability plus corrosion protection at a competitive cost.
2. Mechanical Properties (Per EN 10346)
| Property | DX51D+Z Guarantee |
|---|---|
| Minimum yield strength (ReH) | 140 MPa |
| Tensile strength (Rm) | 270 – 500 MPa |
| Minimum elongation A80 | 22 % (thickness dependent) |
| Steel number | 1.0917 |
These are the EN 10346 minimum guarantees for the base steel; the zinc coating does not change the core mechanical properties of the substrate. For tighter formability requirements, the EN 10346 family moves up the ladder to DX52D (1.0918, A80 ≥26 %), DX53D (1.0919, A80 ≥30 %) and higher. The acceptance values for a specific delivery are stated in the mill test certificate.
3. Typical Chemical Composition (Ladle Analysis, Max %)
DX51D is a low-carbon steel: carbon is typically limited to about 0.12 % max with controlled manganese, phosphorus and sulphur (typically ≤0.10 % C, ≤0.50 % Mn, ≤0.045 % P, ≤0.045 % S as common commercial limits - the exact maxima are agreed between mill and purchaser per EN 10346). The low carbon content is what gives DX51D its excellent formability and weldability, making it suitable for mass industrial processing such as roll forming, stamping and resistance welding.
4. Zinc Coatings and What to Choose
| Coating designation | Minimum total coating mass, both surfaces (g/m², triple-spot) | Typical coating thickness per surface (µm, guidance) |
|---|---|---|
| Z100 | 100 | ≈ 7 |
| Z140 | 140 | ≈ 10 |
| Z180 | 180 | ≈ 13 |
| Z200 | 200 | ≈ 14 |
| Z225 | 225 | ≈ 16 |
| Z275 | 275 | ≈ 20 |
| Z350 | 350 | ≈ 25 |
Cathodic protection is proportional to coating mass: heavier coatings protect longer outdoors, while lighter coatings form better on tight bends. Zinc (Z) is the standard system - lead-free, finely crystallized, with spangle controlled from regular to zero. ZF (galvannealed, ~10 % iron) suits painted products and resistance welding. ZA (zinc-aluminium, ~95/5 eutectic) improves corrosion and forming behaviour. ZM (zinc-aluminium-magnesium) offers a further step in cut-edge protection for coastal or corrosive service. Besides the standard classes, asymmetric coatings, equal-minimum-mass coatings, and OEM specifications are available on request.
5. Surface Quality, Finish and Supply Forms
EN 10346 defines surface quality classes for coated products - commonly A (best, for high-gloss painted finishes), B (improved, for quality painted parts) and C (standard, for general forming). In addition, specify: spangle type (regular, minimized, zero), surface treatment (chromated, chromate-free, or oiled/dry), and the form of supply - full coil, slit coil, or cut-to-length sheet. DX51D+Z is supplied in thicknesses from about 0.3 mm upward and widths typically 600–1500 mm; confirm exact ranges with the mill for your size.
6. Formability and Applications
DX51D covers general forming: light bending, roll forming, simple stamping and folding. For deep drawing or severe stretching, move to DX52D/DX53D. Typical applications of DX51D+Z: roof and wall cladding, purlins, cable trays, electrical enclosures, HVAC components, fencing, storage racks, and semi-exposed industrial parts. For outdoor structural members, consider EN 10346 structural grades (S250GD–S550GD); for exterior architectural parts in corrosive atmospheres, evaluate ZM or ZA systems with appropriate coating mass.
Frequently Asked Questions
What does DX51D+Z Z275 mean? DX51D is the base steel grade; +Z means hot-dip zinc coating; Z275 means the minimum total coating mass on both surfaces is 275 g/m² (triple-spot test). Z275 is a heavy, widely used coating for outdoor and long-life applications.
Is DX51D suitable for deep drawing? No - DX51D is for general forming and simple bending. For deep drawing, select DX52D or DX53D, which guarantee higher elongation (≥26 % and ≥30 % respectively) and better r-/n-values.
Can DX51D Z275 be used outdoors? Yes. Z275 provides strong corrosion resistance for outdoor construction, fencing, profiles and piping components. For coastal or industrial atmospheres, consider Z350 or zinc-aluminium-magnesium (ZM) coatings, and design details to avoid water traps.
What is the difference between DX51D and DX52D? DX51D guarantees minimum elongation 22 % (A80) for general forming; DX52D guarantees ≥26 % with a lower tensile ceiling, giving more headroom for complex forming operations.
Can DX51D+Z be supplied as slit coil or sheets? Yes - full coils, slit coils, and cut-to-length sheets are standard. Specify width tolerance, camber, and edge trimming requirements with your order.
What are the common equivalents of DX51D? In other systems, comparable galvanized grades exist under ASTM A653, JIS G 3302 (e.g., SGCC-type commercial grades) and national standards, but property guarantees and coating classes differ - always verify against the governing standard of your contract before treating grades as interchangeable.
