- Z275 equates to about 19 μm per face on average, while cut edges are exposed.
- Post-fabrication galvanizing gives broad coverage, often around 45–85 μm mean requirements.
- Hollow fabrications require correctly placed vents and drains.
- Weld repair, wet-storage-stain prevention and packing matter too.
Values in this guide are practical starting points for RFQ, DFM and prototype validation. They do not replace load calculations, regulations, material certificates, qualified procedures or approved production drawings.
Pre-galvanized Sheet: Efficient Forming, Exposed Edges
In EN 10346, Z275 denotes 275 g/m² total zinc mass across both faces. Using pure-zinc density gives roughly 38.5 μm total, about 19 μm per face on average; actual alloy layers and distribution vary. It is efficient for stamping and forming, but laser edges, punched edges and welds expose steel. Adjacent zinc may protect small edges sacrificially, yet wet, coastal or water-trap locations still need zinc-rich repair, thermal spray, sealing or an overall coating.
Post-fabrication Hot-dip Galvanizing
Galvanizing after welding and drilling coats accessible external and internal surfaces. ISO 1461:2022 sets minimum local/mean thickness by material thickness, with typical mean requirements in the approximately 45–85 μm range. Allow for buildup in holes, threads and telescopic joints. Precision female threads may be retapped after galvanizing or designed with a coating-compatible allowance.
Electroplated Zinc Is Usually Not the First Choice for Open Exposure
Zinc electroplate in the 5–25 μm range with passivation can suit fasteners, small hardware and sheltered/maintainable locations. Thin coatings are consumed faster under rain, salt and abrasion. If used, specify thickness, passivation/sealer, contact-corrosion controls and maintenance—not merely “clear zinc.”
Venting and Drainage Are Safety and Quality Features
Enclosed hollow sections require high-point venting and low-point drainage for hot-dip galvanizing, placed close to ends and sealed joints. Hole size and count depend on volume, section, immersion orientation and galvanizer rules; two arbitrary holes added after design freeze are not adequate. Avoid sealed overlaps or design them for venting and drainage with galvanizer DFM input.
Welding and Repair Must Match the Final System
Welding pre-galvanized stock requires fume controls and a suitable procedure, followed by oxide/spatter removal. Repair methods under the project specification may include zinc-rich paint, thermal-sprayed zinc or low-melting zinc alloy. Agree thickness, overlap and appearance. If powder follows, every repair material must be compatible with pretreatment and bake temperature.
Prevent Wet-storage Stain
Fresh zinc can develop wet-storage stain when damp surfaces are tightly packed without airflow. Cool and dry parts before packing, separate layers and do not seal rain-wet steel in plastic. Sea shipment may need desiccant and condensation control. Light white stain is not red rust, but severe deposits can consume zinc and require agreed evaluation and treatment.
SELECTION LOGIC
Formed sheet with repairable cut edges: pre-galvanized sheet.
Welded frame in long-term open exposure: evaluate post-fabrication hot-dip galvanizing first.
Small, sheltered, dimension-sensitive hardware: consider zinc electroplating.
Coastal/high-corrosion exposure with color: evaluate a galvanized duplex coating system.