DX51D galvanized coil is the most common specification for roofing and cladding sheet worldwide. It is a ductile, formable grade that roll forms into trapezoidal profiles, corrugated sheets and flashings, and it takes a wide choice of metallic coatings. The selection job for a roofing buyer is therefore mostly about the coating, not the steel: choosing the right coating family and mass for the climate.
What Is DX51D?
DX51D is a continuously hot-dip coated steel grade of EN 10346 for cold forming. It has a maximum carbon content of 0.18%, a tensile range of 270-500 MPa and a minimum elongation of 22%, with yield strength not specified. It is ductile enough for roll forming and light bending, which is exactly what roofing profiles require, and its low-carbon base welds and fastens without special treatment.
Thickness and Width Range
DX51D roofing coil is commonly supplied from 0.30 mm to 3.00 mm, with widths up to about 1520 mm; the most used roofing gauges are 0.35 mm to 0.80 mm for profiled sheet and up to 1.50 mm for heavier cladding. Thickness tolerance, flatness and width follow EN 10346 and should be confirmed against the roll former's requirements, because profile geometry depends on consistent gauge.
DX51D versus DX52D
DX52D is an improvement over DX51D in formability: it guarantees a yield range of 140-300 MPa, tensile of 270-420 MPa and elongation of at least 26%, with lower carbon, manganese and phosphorus limits. For roofing profiles the forming demands are modest, so DX51D is the economical standard; DX52D is chosen for components with deeper stamping or tighter bends, such as flashings with complex geometry or pressed accessories.
Coating Options for Roofing
| Coating | Composition | Roofing role |
|---|---|---|
| Z100-Z140 | Pure zinc, 100-140 g/m2 | Painted roofing in moderate climates |
| Z200-Z275 | Pure zinc, 200-275 g/m2 | Bare or painted roofing, standard service life |
| AZ150 | Aluminium-zinc, 150 g/m2 (55% Al, 43.4% Zn, 1.6% Si) | Coastal, industrial and heat-exposed roofing; long bare service life |
AZ150 delivers superior corrosion performance under varied conditions compared with pure zinc at equal mass, particularly at cut edges and in warm, humid or salt-laden air, which is why it dominates premium roofing specifications.
Why Roofing Coils Are Commonly Pre-Painted
Most roofing coil is colour-coated (PPGI) before roll forming: the paint system adds colour, reflects heat and protects the zinc surface, while the zinc remains the corrosion backstop at cut edges and scratches. The coating mass under the paint should not be reduced below the design value, because the edges and fastener holes depend on the zinc layer for decades of service.
Frequently Asked Questions
1. Is DX51D the same as SGCC?
They are the EN and JIS designations for the same product type, a hot-dip coated low-carbon forming grade; DX51D is used in EN 10346 supply and SGCC in JIS G3302 supply.
2. What does AZ150 mean?
AZ150 is an aluminium-zinc coating of 150 g/m2 total, containing about 55% aluminium, 43.4% zinc and 1.6% silicon, applied by continuous hot-dip coating; the aluminium gives a dense barrier and heat reflectivity, the zinc gives sacrificial edge protection.
3. Which coating lasts longer on a roof, Z275 or AZ150?
In most environments AZ150 offers a longer maintenance-free life despite the lower mass, especially at cut edges and in coastal or industrial air; Z275 pure zinc is the heavier, traditional choice for interior and standard service.
4. Can DX51D roofing coil be bent sharply for flashings?
Yes, DX51D bends well within the elongation guarantee of 22%; for very tight radii use DX52D or a spangle-free surface to avoid coating micro-cracks at the bend.
5. What is the standard coil width for roofing profiles?
Roofing coil is usually supplied in 1000-1250 mm widths, and sometimes pre-cut to the exact profile width after slitting; confirm the roll former's required width before ordering.
6. How is coating quality verified?
The mill certificate states the coating class and test results (triple-spot mass, bend and adhesion tests); buyers can verify coating mass by stripping and weighing samples or with a magnetic thickness gauge.