What is Zn-Al-Mg coated steel?
Zinc-aluminum-magnesium coated steel is steel sheet protected by a hot-dip metallic alloy coating containing zinc, aluminum and magnesium. The base steel supplies the specified mechanical properties; the coating changes corrosion behavior. Coating chemistry, coating mass and steel grade are separate requirements.
Zn-Al-Mg describes a family, not a single recipe. ZAM, SuperDyma and Magnelis are commercial product names within that family, with different published compositions. A request for “ZAM coating” should identify whether it means Nippon Steel’s branded product or a generically described Zn-Al-Mg coating. Do not substitute one for the other without checking the actual specification. Nippon Steel’s ZAM Q&A identifies its product and composition.
For the wider material context, start with steel coil and the Steel Types directory.
Two Mg-containing families, separate standards
| Dimension | What it establishes | What it does not establish |
|---|---|---|
| Chemistry | Zn-Al-Mg versus 55% Al-Zn-Mg-Si; identify the actual alloy family. | The presence of Mg does not make these the same coating. |
| Product standard | A1046/A1046M-25a covers Zn-Al-Mg sheet; A792/A792M-25a Type 2 belongs to the 55% Al-Zn family. | A named brand does not automatically comply with either document. |
| Coating designation | The selected standard’s coating class, mass basis and test context. | Substrate grade, commercial identity or an automatic cross-standard equivalent. |
| Producer brand | A named producer/product and its published evidence. | ZAM, Magnelis and SuperDyma are not synonyms or blanket equivalents to A1046. |
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The official scopes for A1046/A1046M-25a and A792/A792M-25a were checked active on 18 September 2026. A792 Type 1 is Al-Zn-Si; Type 2 adds Mg within that standard’s aluminum-rich family. Orders retain their specified editions and require the full applicable requirements. A public abstract cannot certify a branded product.
Composition and commercial examples
The following are producer-published examples, not allowable limits for every Zn-Al-Mg product. Percentages refer to the metallic coating, not the base steel. Verify the current product data and order requirements.
| Product example | Producer's published composition | Source |
|---|---|---|
| ZAM™ | Zinc with approximately 6% aluminum and 3% magnesium. | Nippon Steel — ZAM Q&A |
| SuperDyma™ | Zinc with about 11% aluminum, 3% magnesium and a small silicon addition. | Nippon Steel — product composition |
| Magnelis® | 93.5% zinc, 3.5% aluminum and 3% magnesium. | ArcelorMittal — Magnelis |
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Keep the named producer and product designation with each composition when comparing offers.
Corrosion protection mechanism
Protection involves both the metallic layer and the corrosion products that develop at its surface. Zinc can provide sacrificial protection to exposed steel. Aluminum and magnesium additions affect coating structure and the protective surface film; performance therefore cannot be inferred from zinc coating mass alone.
For SuperDyma specifically, Nippon Steel describes a compact protective film containing zinc- and magnesium-bearing corrosion products. Its mechanism description applies to that named product. SuperDyma materials catalogue.
Cut-edge protection and its limits
Cutting exposes the steel underneath the coating. Protective corrosion products from the surrounding coating can develop over the exposed edge. Initial red rust is still possible; the producer’s description of a protective film must not be read as a guarantee of an immediately rust-free edge. Nippon Steel’s cut-end explanation.
Check sheet thickness, cut quality, exposure, drainage and any edge-treatment requirements for the selected product. The term “self-healing” used in some product literature describes corrosion-protection behavior: it does not mean that the steel regenerates or that a damaged coating returns to its original thickness.
Forming considerations
Select a base-steel grade for the required deformation first. Then check coating adhesion, bend radius, tooling, lubrication and the intended surface treatment. Trial the actual grade, thickness and coating through the proposed bend geometry.
ArcelorMittal lists bending, drawing, profiling, stamping and welding among the processing operations for Magnelis. Those product capabilities should be checked against its grade-specific requirements rather than transferred to all Zn-Al-Mg products. Magnelis processing data.
Specify the condition of sheared edges, punched holes and formed corners. Welding locally changes the protective system; use the selected product’s welding and repair instructions. For profiled building components, also read the corrugated steel sheet guide .
Applications
Producer literature includes building components, photovoltaic support structures and HVAC equipment. These are application examples rather than approvals for any environment or load. ArcelorMittal’s product overview and HVAC material guidance provide context.
For a project, establish the exposure on both faces, water retention, contact metals and connection details. A coating designation does not replace structural sizing, fire requirements or a roof-system specification.
Galvanized vs Galvalume vs Zn-Al-Mg
| Family | Metallic coating | Selection question |
|---|---|---|
| Galvanized | Zinc coating. | Which coating designation, surface treatment and base grade suit the application? |
| Galvalume / Al-Zn | The conventional 55% aluminum-zinc coating family. | What are the product's forming, exposure and cut-edge requirements? |
| Zn-Al-Mg | Zinc, aluminum and magnesium; composition depends on the product. | Which specific chemistry and product evidence support the proposed use? |
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The Galvalume explanation gives its coating source and specification context. A paint finish is another layer of the specification; see prepainted steel coil .
Specification considerations
| Field | Record explicitly |
|---|---|
| Product identity | Generic coating family, named commercial product if required, producer and supporting technical data. |
| Steel grade | Mechanical requirements and formability; keep base-metal chemistry separate from coating chemistry. |
| Coating | Composition, designation, mass basis, whether values cover both sides, and applicable test requirements. |
| Dimensions | Nominal base-metal thickness, width, tolerances and edge condition. |
| Surface and fabrication | Treatment, oiling, painting, bend requirements, joining and treatment of cut or welded areas. |
| Exposure | Application, environment, contact materials and relevant product restrictions. |
| Standard | Exact standard, edition, grade and coating designation; do not assume equivalence between systems. |
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ASTM A1046/A1046M covers hot-dip Zn-Al-Mg coated sheet in coils and cut lengths. Its public scope is not a certificate for a particular branded product. Obtain the applicable full specification and material documentation. The standards reference explains why grade, coating and test standards must be read separately.