1. Design Considerations
(1) Allow Proper Weathering
Initial Rust Formation:
The steel will develop a protective patina (stable rust layer) over 6–24 months.
Early rust may stain adjacent surfaces (e.g., concrete)-use temporary drip edges or rust inhibitors if needed.
Drainage & Ventilation:
Avoid water traps (e.g., horizontal ledges, crevices) where moisture can accumulate.
Design sloped surfaces and drainage holes to prevent stagnant water.
(2) Avoid Galvanic Corrosion
Do not directly connect to dissimilar metals (e.g., aluminum, stainless steel).
Solution: Use insulating spacers (rubber, plastic) or protective coatings at contact points.
(3) Fatigue & Stress Resistance
SMA490AW is notch-sensitive-avoid sharp corners in design.
Use rounded transitions and smooth weld profiles to reduce stress concentrations.
2. Fabrication & Welding
(1) Cutting & Machining
Can be cut via plasma, laser, or oxyfuel methods.
Grinding/Drilling: Use carbide tools for best results (harder than mild steel).
(2) Welding Procedures
| Method | Recommended Filler Metal | Preheat (if needed) |
|---|---|---|
| SMAW (Stick) | E7018 (low-hydrogen) | 100–150°C (for >25mm thickness) |
| GMAW (MIG) | ER70S-6 or ER80S-Ni1 | Same as above |
| FCAW | E71T-1 (flux-cored) | Same as above |
Post-Weld Cleaning: Remove slag/spatter to prevent localized corrosion.
Avoid Excessive Heat Input: Can weaken the heat-affected zone (HAZ).
3. Surface Treatment & Maintenance
(1) Natural Patina Development
Do not paint unless required-the rust layer is the protective feature.
Accelerating Patina Formation:
Light water spraying in dry climates.
Commercial weathering accelerators (e.g., diluted acetic acid).
(2) Cleaning & Repairs
Normal Conditions: Let the patina develop naturally.
Heavy Staining/Corrosion:
Light sandblasting (avoid removing the stable patina).
Apply weathering-resistant primer if recoating is necessary.
