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Z275 means the specified zinc coating has a minimum total mass of 275 g/m² across both sides of the sheet under the applicable standard’s test method. It does not mean 275 g/m² on each side, and it does not describe the base-steel grade, sheet thickness, spangle, passivation or surface quality.
New Star Steel offers Galvanized Steel Coil with coating, surface and coil parameters matched to the order.
The “Z” identifies a zinc coating. “275” identifies the required total coating mass in grams per square metre, combining the two coated surfaces. Continuous hot-dip lines do not always distribute zinc perfectly equally between both sides, so standards define sampling and multi-spot acceptance rules.
ASTM A653/A653M’s published table lists Z275 as a total-both-sides SI coating designation and G90 as the familiar inch-pound designation. They are commonly compared because the specified coating mass is in the same general class, but orders should use the designation belonging to the invoked standard rather than treating the names as freely interchangeable.
Coating mass can be converted to an approximate average thickness using zinc density. A Z275 total coating mass corresponds to roughly 38.5 µm of zinc combined across both sides, or about 19 µm per side if distribution is equal. This is an engineering approximation, not a guarantee of equal single-side thickness.
| Designation | Minimum total coating mass | Approximate total zinc thickness |
|---|---|---|
| Z100 | 100 g/m² | About 14 µm combined |
| Z180 | 180 g/m² | About 25 µm combined |
| Z275 | 275 g/m² | About 38.5 µm combined |
| Z350 | 350 g/m² | About 49 µm combined |
Approximate values use a zinc density near 7.14 g/cm³. Use measured coating mass or a contractually agreed thickness method for acceptance.
Within a comparable exposure and coating system, a heavier zinc layer generally provides more sacrificial material and therefore a larger corrosion reserve. ASTM’s published notes explain that atmospheric corrosion resistance is a direct function of coating thickness/mass and that selecting a lighter coating reduces corrosion performance.
Actual life also depends on moisture, chlorides, sulfur compounds, temperature, sheltering, cut edges, fabrication damage, drainage, contact with dissimilar metals and maintenance. Z275 is not a universal design-life promise.
Standards may use multi-spot and single-spot requirements. Production control can include X-ray fluorescence gauges, magnetic/electromagnetic methods and laboratory mass-loss testing. The purchase order should state the standard, designation, test basis and whether a special single-side distribution is required.
Heavier coatings change tool contact and can increase zinc pickup during forming. During welding, zinc fumes require properly engineered ventilation and procedures. For painting, passivation chemistry, oil, surface texture and pretreatment compatibility are as important as coating mass.
If appearance is critical, also choose the crystallization pattern using our spangle selection guide.
No. It is 275 grams per square metre total coating mass. The approximate combined thickness is only about 38.5 micrometres.
They are commonly treated as comparable SI and inch-pound coating classes, but the invoked standard and its test rules remain controlling. Use the correct designation on the order.
No. It specifies coating mass. The base steel could be a forming, structural or other grade and must be stated separately.
For a coating recommendation and quotation, send New Star Steel the environment, fabrication process, target life, size and annual volume.
