Steel Surface Treatment Guide: HDG, Electro-galv & PPGI Explained
Surface treatment is critical when ordering steel — it determines corrosion resistance, appearance, paintability, and total cost. This guide covers the three most common treatments.
1. Hot-Dip Galvanizing (HDG/GI)
Steel immersed in molten zinc at ~450°C. Coating weight: Z100-Z600 (100-600 g/m²). Thickness: 7-85 μm. Spangled or minimum spangle appearance. Standard: JIS G3302, EN 10346, ASTM A653.
2. Electro-Galvanizing (EG)
Zinc deposited through electroplating. Coating weight: Z20-Z100. Thickness: 3-12 μm. Smooth, bright, uniform surface — ideal for painting. Better formability than HDG. Lower cost.
3. Pre-Painted Galvanized Steel (PPGI)
Factory coil coating line applies paint to galvanized/galvalume steel. Systems:
| Paint Type | Durability | UV Resistance | Cost |
|---|---|---|---|
| PE (Polyester) | 5-10 years | Moderate | $ |
| SMP (Silicone Modified) | 10-15 years | Good | $$ |
| HDP | 15-20 years | Very Good | $$$ |
| PVDF | 20-30+ years | Excellent | $$$$ |
How to Choose
- HDG: Long-term outdoor protection, harsh environments, structural
- Electro-galv: Smooth surface for painting, complex forming, indoor
- PPGI: Both protection AND color needed, architectural, appliance
CoreMetal supplies all three types. Contact Tracy at tracy@coremetalsteel.com or +86 18291910632.