AS/NZS Coated Steel Coil Guide: Australian & NZ Grades, Coatings & Ordering Basics

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AS/NZS Coated Coil Basics (Australia / New Zealand)

Engineering & Procurement Guide for Roll Forming Applications

Australia and New Zealand operate under a distinct set of standards for coated steel used in:

Roofing
Wall cladding
Structural purlins
Solar mounting
Residential framing
Commercial building systems

The primary standards are:

AS/NZS 1397 – Continuously hot-dip metallic coated steel sheet and strip
AS 2728 – Prepainted and organic film coated steel sheet

Unlike ASTM or EN standards, AS/NZS standards are highly climate-driven due to:

Coastal salt exposure
High UV intensity
Cyclone-prone regions
High temperature environments

Understanding AS/NZS coated coil requirements is critical for any roll forming manufacturer supplying the Australian or NZ market.

1️⃣ Core Standard: AS/NZS 1397

AS/NZS 1397 covers:

Metallic-coated steel sheet and strip for structural and forming applications

It defines:

Base metal strength
Coating type
Coating mass
Mechanical properties
Thickness tolerances
Surface finish

This is the foundation for roofing and structural coil supply in Australia/NZ.

2️⃣ Structural & Forming Grades

Grades are designated using:

G + Minimum Yield Strength

Examples:

Grade	Minimum Yield Strength
G250	250 MPa
G300	300 MPa
G350	350 MPa
G450	450 MPa
G550	550 MPa

G550 is very common in Australian roofing profiles.

This is higher than many US roofing grades.

2.1 Why Higher Strength Is Common

Australian roofing profiles are often:

Thin gauge (0.42–0.48 mm BMT)
High rib geometry
Long span
Cyclone rated

Higher yield strength compensates for thinner material.

3️⃣ Coating Types Under AS/NZS

Australia/NZ commonly uses three metallic coating types:

3.1 Z (Zinc / Galvanized)

Designation: Z100, Z275 etc.

Used for:

Structural framing
Purlins
Stud systems

3.2 AZ (Aluminium-Zinc)

Equivalent to Galvalume.

Common designation:

AZ150 (150 g/m² total coating)

AZ150 is standard for roofing in Australia.

3.3 AM (Aluminium-Magnesium Alloy)

Newer generation coatings (e.g., ZM equivalent).

Improved corrosion resistance and cut-edge protection.

Increasingly used in:

Solar mounting
Structural framing
Coastal applications

4️⃣ Common Roofing Specification in Australia

Typical roofing coil spec:

G550 – AZ150 – 0.42 BMT – AS/NZS 1397 compliant

BMT = Base Metal Thickness (excluding coating).

Important difference:

Australia often references BMT, not total thickness including coating.

This affects roll forming setup.

5️⃣ Base Metal Thickness (BMT) vs TCT

In AS/NZS:

BMT = Steel thickness only
TCT = Total Coated Thickness

Many global suppliers quote TCT.

Misunderstanding this leads to under-thickness supply.

Example:

0.42 BMT ≠ 0.42 total thickness.

This is a common import mistake.

6️⃣ Corrosion Environment Categories

Australia classifies exposure environments:

C1 (Very low)
C2 (Low)
C3 (Medium)
C4 (High)
C5 (Very high / coastal)

AZ150 performs well in C3–C4 environments.

Coastal C5 areas may require additional protection systems.

7️⃣ Forming Behavior of G550

G550 is high tensile.

In roll forming:

Significant springback
Requires aggressive overbend
Higher forming pressure
Increased shaft load
Increased crack sensitivity

Machines designed only for G250 may struggle with G550.

8️⃣ Coating Performance in Australian Climate

High UV exposure affects:

Paint degradation
Surface chalking
Color fade

Metallic coatings must resist:

Salt spray
High humidity
Thermal cycling

AZ150 performs better than Z275 in many atmospheric conditions.

9️⃣ Prepainted Standards (AS 2728)

AS 2728 governs prepainted steel.

It defines:

Paint system durability
Film thickness
UV resistance
Color retention
Adhesion testing

Common paint systems:

Polyester
SMP
PVDF (high-end)

Paint selection is critical in high UV zones.

🔟 Machine & Tooling Implications

High tensile G550 + AZ150:

Increases forming load
Requires hardened tooling
Requires stable strip tension
Increases edge crack sensitivity

Slit edge quality is critical in G550.

1️⃣1️⃣ Procurement Checklist (Australia/NZ)

A correct order example:

AS/NZS 1397 – G550 – AZ150 – 0.42 BMT – Mill Edge – Skin Passed – AS 2728 Paint (if prepainted)

Always confirm:

Grade (G250, G350, G550)
Coating type (Z, AZ, AM)
Coating mass (e.g., AZ150)
BMT thickness
Surface finish
Compliance documentation
Exposure environment rating

Failure to specify BMT correctly causes disputes.

1️⃣2️⃣ Buyer Strategy (30%)

When to Choose G550

Roofing panels
Cyclone-rated regions
Long-span thin gauge systems

When to Choose G350

Structural purlins
Stud framing
Moderate load-bearing systems

When to Upgrade Coating

Coastal exposure
Solar mounting
Agricultural environments

Common Buyer Mistakes

Confusing BMT with total thickness
Ordering G250 for roofing in cyclone zones
Using Z coating instead of AZ for roofing
Ignoring exposure classification
Not verifying compliance to AS/NZS 1397
Using low-durability paint in high UV zones

6 Frequently Asked Questions

1. What is AZ150?

Aluminium-zinc coating with total mass of 150 g/m² (both sides combined).

2. Why is G550 common in Australia?

Because thinner gauges are used for roofing and must meet structural load requirements.

3. What does BMT mean?

Base Metal Thickness — excludes coating thickness.

4. Is Z275 used for roofing in Australia?

Less common; AZ150 is preferred for corrosion performance.

5. Does G550 increase roll forming difficulty?

Yes. It increases springback and forming force.

6. Should I request compliance certificates?

Yes. AS/NZS compliance is required for structural and warranty approval.

Final Engineering Summary

AS/NZS coated coil standards are climate-driven and structurally focused.

Critical differences compared to ASTM/EN:

BMT measurement standard
High use of G550
Common use of AZ150
UV durability requirements

Correct ordering must define:

Grade
Coating type and mass
BMT thickness
Exposure classification
Compliance documentation

For roll forming manufacturers exporting to Australia or NZ, understanding these nuances prevents under-spec supply, corrosion failure, and warranty exposure.