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Steel Coil Coating Types: Zinc, Al-Zn, PPGI, PVDF
Choosing the right coating for steel coils is critical to ensuring long-term performance, corrosion resistance, and aesthetic value. This guide explores the main coating systems used in the steel industry — zinc (GI), aluminum-zinc (GL or Galvalume), and organic paint systems (PPGI/PPGL) — comparing their composition, coating weights (such as Z180, G90, AZ150), and application suitability across construction, automotive, and appliance sectors.
It also provides expert insights into technical parameters, including coating adhesion, surface treatment standards (ASTM, JIS, EN), and paint layer thickness for PVDF and SMP systems. By understanding each coating’s advantages and cost-performance ratio, manufacturers and buyers can make smarter material selections.
As a trusted global supplier, Hengze Steel offers high-quality galvanized, Galvalume, and pre-painted steel coils with stable coating quality, meeting international standards for durability and surface finish.
Table of Contents
- 1. Executive summary1. Executive summary
- 2. Why Coating Choice Matters2. Why Coating Choice Matters
- 3. Coating Family Overview3. Coating Family Overview
- 4. Technical Parameters & Performance Comparison4. Technical Parameters & Performance Comparison
- 5. Coating Selection Guide (by Environment & Application)5. Coating Selection Guide (by Environment & Application)
- 6. Standards & Test Methods6. Standards & Test Methods
- 7. Specification & Procurement Checklist7. Specification & Procurement Checklist
- 8. FAQs & Common Issues8. FAQs & Common Issues
- 9. Conclusion9. Conclusion
1. Executive summary
Coated steel coils—whether Galvanized (GI), Galvalume (GL), or Pre-painted (PPGI/PPGL)—are fundamental in construction, automotive, and manufacturing industries.
The coating composition, thickness, and adhesion performance determine the product’s corrosion resistance, forming behavior, and durability.
Zinc coatings (Z) provide sacrificial cathodic protection.
Al-Zn coatings (AZ) combine aluminum’s barrier action with zinc’s galvanic protection.
Organic paint systems (PE, SMP, PVDF) extend color retention, weather resistance, and design flexibility.
Hengze Steel supplies a full range of GI, GL, PPGI, and PPGL coils manufactured to ASTM, EN, and JIS standards—engineered for durability, surface precision, and consistent coating integrity.
2. Why Coating Choice Matters
The coating is not just a surface finish—it defines service life.
According to ASTM B117 and ISO 9227 salt spray testing:
A typical Z275 (G90) galvanized coating offers up to 500–600 hours before red rust.
AZ150 Galvalume coatings exceed 2,000–2,500 hours, depending on environment.
PVDF pre-painted systems can resist color fading for 20–30 years in tropical climates.
Coating systems also affect:
Formability (minimum bend radius, ASTM E290)
Weldability (impact of coating type on resistance welding current range)
Paint adhesion (cross-hatch test per ISO 2409 / ASTM D3359)
Reflectivity (aluminized and Al-Zn coatings offer >75% solar reflectance)
Hengze Steel’s continuous coating lines use precise air-knife control and X-ray gauge systems to ensure uniform coating weight and tight tolerances.
3. Overview of Coating Families
3.1 Zinc-Based Coatings (HDG, EG, Galvanneal)
| Type | Process | Typical Coating Weight | Key Properties | Standards |
|---|---|---|---|---|
| HDG (Hot-Dip Galvanized) | Molten zinc immersion | Z100–Z600 (70–425 g/m²) | Excellent corrosion protection; suitable for structural and general use | ASTM A653, EN 10346 |
| EG (Electrogalvanized) | Electroplating | 10–60 g/m² | Smooth finish, ideal for automotive inner panels | ASTM A879 |
| Galvanneal (Zn-Fe) | HDG + annealing | Z100–Z180 | Enhanced paint adhesion; reduced powdering during forming | JIS G3313 |
3.2 Aluminum-Zinc (Al-Zn) Alloy Coatings
Composition: Al 55%, Zn 43.4%, Si 1.6%.
Density: 3.75 g/cm³ (lighter than pure Zn).
Typical coating mass: AZ70–AZ200 (50–150 g/m² per side).
| Property | Galvanized (Z275) | Galvalume (AZ150) |
|---|---|---|
| Salt Spray Resistance | ~500 h | 2000–2500 h |
| Heat Reflectivity | 55% | 75% |
| Edge Protection | Cathodic | Barrier + Cathodic |
| Lifespan (rural area) | 10–15 yrs | 25–40 yrs |
Hengze Steel’s Galvalume coils (AZ50–AZ150) are certified to ASTM A792 / JIS G3321 and widely used in roofing, cladding, and solar mounting systems.
3.3 Aluminized Steel Coatings
Type 1 (Al-Si 90/10): High oxidation resistance up to 650°C.
Type 2 (Pure Al): Excellent heat reflectivity for exhaust systems.
Applications: Heat shields, ovens, catalytic converters.
3.4 Organic Paint Systems (PPGI / PPGL)
Layer Structure: Pretreatment → Primer (5–7 µm) → Topcoat (15–25 µm) → Backcoat (5–10 µm).
| Paint Type | Thickness | Gloss | UV Resistance | Service Life |
|---|---|---|---|---|
| PE (Polyester) | 15–20 µm | 60–80% | Moderate | 10–15 yrs |
| SMP (Silicone Modified Polyester) | 20–25 µm | 40–60% | Good | 15–25 yrs |
| PVDF (Fluorocarbon) | 25–30 µm | 30–40% | Excellent | 25–40 yrs |
Performance Metrics:
Adhesion: ≤ Class 1 (ASTM D3359)
Impact Resistance: ≥ 18 J (ASTM D2794)
Gloss Retention: > 80% after 4000 h QUV exposure (ASTM G154)
Hengze Steel’s pre-painted lines use Henkel & Chemetall pretreatments and high-quality paints from AkzoNobel & Beckers for superior UV and corrosion resistance.
3.5 Hybrid & Advanced Coating Systems
Al-Zn-Mg (ZAM®): Adds 1–3% Mg and 1.5% Si → up to 10× higher edge protection.
Anti-Fingerprint Coating (AFP): Thin transparent passivation film (<0.3 µm) improving handling cleanliness.
Laminate Coatings: Metallic substrate + PET or PVC film → used for interior panels and home appliances.
4. Technical Parameters & Performance Comparison
| Parameter | Symbol / Unit | Typical Range | Importance |
|---|---|---|---|
| Coating Mass | g/m² | Z100–Z600 / AZ70–AZ200 | Corrosion protection |
| Coating Thickness | µm | 7–45 | Directly affects lifespan |
| Adhesion (Cross Cut) | ISO 2409 Class | ≤ Class 1 | Coating integrity |
| Bending Radius | t (thickness ratio) | 0–3t | Formability |
| Salt Spray Resistance | Hours | 500–2500 | Environmental durability |
| Pencil Hardness | ASTM D3363 | H–3H | Scratch resistance |
All Hengze Steel coils undergo triple-spot coating weight inspection and full adhesion testing before shipment.
5. Coating Selection Guide (by Environment & Application)
| Environment | Recommended Coating | Coating Weight | Paint Type | Notes |
|---|---|---|---|---|
| Indoor | EG / light GI | Z100–Z180 | Optional | Decorative & easy forming |
| Mild Outdoor | GI | Z275 | PE / SMP | Affordable protection |
| Coastal / Industrial | GL / ZAM | AZ150+ | PVDF | Superior corrosion resistance |
| High Temp (Furnace, Exhaust) | Al-Si | — | — | Oxidation resistance up to 650°C |
| Decorative Façade | PPGL | AZ150 | PVDF | Long color retention |
6. Standards & Test Methods
ASTM A653 / EN 10346 — Hot-dip galvanized steel
ASTM A792 / JIS G3321 — Al-Zn coated steel
ASTM D3363, D3359, D2794 — Paint hardness, adhesion, impact tests
ISO 9227 / ASTM B117 — Salt spray corrosion
ASTM E290 — Bend test
7. Specification & Procurement Checklist
✅ Specify coating type, standard, and mass (e.g., AZ150, ASTM A792).
✅ Confirm steel grade (DX51D, S350GD, ASTM A792 SS Grade 37).
✅ Require coating certificate + third-party inspection.
✅ Define paint system, color (RAL code), and DFT.
✅ Ensure anti-moisture packaging (VCI paper, wooden pallets).
8. FAQs & Common Issues
Q1. What is the difference between GI and GL?
→ GI is zinc-only; GL has 55% aluminum for higher durability (2–6× lifespan).
Q2. Is PVDF worth the extra cost?
→ Yes, for high UV exposure or coastal use. PVDF retains color >80% even after 20 years.
Q3. How to prevent white rust during storage?
→ Use dry, ventilated storage and apply oil/passivation; Hengze Steel provides AFP (anti-fingerprint) options.
9. Conclusion
Selecting the correct coating depends on service environment, coating weight, and desired lifespan.
For most outdoor applications, Galvalume (AZ150) or PVDF-coated PPGL provides optimal performance and long-term cost efficiency.
Hengze Steel’s advanced continuous galvanizing and pre-painting facilities ensure consistent quality, verified coating weights, and superior corrosion performance — trusted by global clients in more than 60 countries.
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