DX51D, DX52D and DX53D are the three most commonly ordered continuous hot-dip galvanized grades in the EN 10346 system. The substrate is cold-rolled low-carbon strip, and the zinc layer is applied by continuous hot-dip galvanizing. The designation Z275 means a nominal coating mass of 275 g/m2 measured on both surfaces, triple-spot minimum per EN 10346, which corresponds to roughly 19-20 micrometres of zinc per side. This combination of a formable cold-rolled substrate and a substantial zinc layer makes the product a standard choice for roofing, purlins, air ducts, appliance housings and general sheet metal work.
Reading the grade designation
All three grades share the same structure: D for flat product for cold forming, X for unspecified rolling condition, and a number that ranks formability. DX51D is the commercial grade for bending and simple forming; DX52D adds deeper drawing capability; DX53D is the deep-drawing grade of the family, with the softest substrate and the highest elongation guarantee. For the same Z275 coating, moving from DX51D to DX53D improves the ability to withstand stretching and deep drawing without cracking of the coating or the base metal.
| Grade | Yield strength Rp0.2 (MPa) | Tensile strength Rm (MPa) | Elongation A80 min (%) | Typical use |
|---|---|---|---|---|
| DX51D+Z275 | 140-300 | 270-500 | 22 | Roll forming, bending, profiles |
| DX52D+Z275 | 140-300 | 270-420 | 24 | Light drawing, press work |
| DX53D+Z275 | 140-260 | 270-380 | 28 | Deep drawing, complex parts |
The values above are for thickness 0.35-3.0 mm as given in EN 10346; actual mill certificates may show tighter values. Note that the elongation is measured with an A80 gauge for these grades, so do not compare it directly with A50 values from other standards.
What Z275 means for the coating
Z275 is a coating mass designation, not a thickness. EN 10346 requires a minimum triple-spot value of 275 g/m2 for the total coating on both surfaces, with a single-spot minimum of 235 g/m2. At the standard conversion of about 7.1 g/m2 per micrometre per side, Z275 corresponds to roughly 19-20 micrometres of zinc per side. Heavier coatings protect longer but reduce formability slightly and increase cost; Z275 is a middle-of-the-range choice that suits roofing, agricultural buildings, cable trays and appliance parts where good corrosion resistance and acceptable bendability are both required.
Substrate quality and welding practice
The cold-rolled substrate is low-carbon steel, normally aluminium-killed, which gives clean bending edges and predictable behaviour in roll forming. For welding, the zinc layer must be taken into account: zinc vapour forms at welding temperature, so joints should be made with adequate fume extraction, and MIG/MAG or resistance spot welding is preferred over manual arc welding for thin material. Where the coating is removed by grinding before welding, the exposed steel should be protected afterwards with a zinc-rich repair coating so that the cut edge and weld zone do not corrode faster than the surrounding coated surface.
How to choose between the three grades
Start from the forming operation. If the part is bent or roll-formed with a bend radius of about one to two times the sheet thickness, DX51D is normally sufficient. If the part is drawn into a shallow cup or pressed with moderate stretching, DX52D gives a safety margin. If the part is deep drawn, for example a housing or an automotive inner panel, DX53D is the correct starting point. When in doubt, order a trial coil of the softer grade and verify the coating behaviour on the actual tool; the cost difference between adjacent grades is small compared with a failed die trial.
Frequently asked questions
1. What does Z275 mean in grams and microns?
Z275 means a total zinc coating mass of 275 g/m2 on both surfaces, triple-spot minimum per EN 10346, equal to about 19-20 micrometres per side. The single-spot minimum is 235 g/m2.
2. Is DX51D+Z275 suitable for roofing?
Yes. DX51D+Z275 is one of the most common choices for roofing profiles, wall cladding and purlins, where it is roll-formed into trapezoidal or corrugated profiles. For coastal or industrial atmospheres, a heavier coating or a zinc-aluminium coating such as AZ150 should be considered.
3. What is the difference between DX51D and DX53D?
DX53D has a softer substrate with higher guaranteed elongation, 28% versus 22% for DX51D at A80, and a narrower strength range, which allows deeper drawing without cracking. The coating is the same; only the base steel formability differs.
4. Can Z275 coil be deep drawn?
Yes, within the limits of the grade. For deep drawing use DX53D+Z275 and check the bend radius and tool geometry against the coating. Very sharp radii can crack the zinc layer even when the base steel survives; a small radius increase or a softer grade usually solves the problem.
5. How is the Z275 coating verified on delivery?
The coating mass is verified by weighing a sample before and after stripping the zinc, normally per the gravimetric method of GB/T 1839-2008, or by non-destructive fluorescent X-ray measurement on the strip. The mill certificate should state the triple-spot and single-spot values.
6. Why is the product called cold-rolled if it is galvanized?
The substrate is cold-rolled strip, which is then cleaned, annealed and passed through the zinc bath on a continuous galvanizing line. So the final product is a hot-dip galvanized coil made from a cold-rolled base.