Galvalume steel coils typically have a Rockwell hardness of 50–65 HRB, Vickers hardness of 85–120 HV, and Brinell hardness of 70–100 HB, varying by steel grade, coating thickness, and production process. As a hot-dip aluminum-zinc alloy coated steel (55% Al, 43.4% Zn, 1.6% Si), its hardness balances formability and wear resistance, making it ideal for construction, automotive, and appliance applications.
Core Definition: Hardness of Galvalume Steel Coils
Hardness of galvalume steel coils refers to the material's resistance to indentation, scratching, and deformation, determined by the cold-rolled steel substrate and aluminum-zinc alloy coating. The substrate (low-carbon steel) provides ductility, while the 55% Al–43.4% Zn–1.6% Si coating (solidified at ~600°C) enhances surface hardness and corrosion resistance. This dual structure results in moderate hardness (50–65 HRB)-higher than pure galvanized steel (40–50 HRB) but lower than high-strength carbon steel (≥70 HRB).
Standard Hardness Values by Grade
Galvalume hardness varies significantly by steel grade (CQ, DQ, S-series) and substrate strength, with standardized ranges per international norms (ASTM A792, EN 10346).
| Grade | Rockwell Hardness (HRB) | Vickers Hardness (HV) | Brinell Hardness (HB) | Key Feature |
|---|---|---|---|---|
| CQ (Commercial Quality) | 50–71 | 90–120 | 75–100 | General-purpose, good formability |
| DQ (Drawing Quality) | 45–55 | 85–100 | 70–85 | Deep-drawing, ultra-ductile |
| S250GD+AZ | 52–60 | 95–110 | 80–95 | Structural, yield strength ≥250 MPa |
| S350GD+AZ | 58–65 | 105–120 | 90–100 | High-strength structural, yield strength ≥350 MPa |
| G550+AZ | 65–75 | 115–130 | 95–105 | Ultra-high strength, yield strength ≥550 MPa |
Key Factors Affecting Hardness
1. Substrate Steel Grade
The cold-rolled substrate dominates base hardness: low-carbon steel (CQ/DQ) has lower hardness (45–55 HRB) for bending/forming, while high-strength low-alloy (HSLA) steel (S280GD–S550GD) increases hardness (58–75 HRB) via grain refinement and alloying elements (Mn, Si).
2. Coating Thickness & Composition
Thickness: Heavier coatings (AZ150–AZ275) raise surface hardness by 5–10 HV due to increased Al–Zn alloy volume.
Silicon Content: 1.6% Si refines the coating's crystalline structure, boosting hardness by ~15% compared to silicon-free Al–Zn coatings.
Alloy Modifications: Magnesium-added galvalume (Al–Zn–Mg) increases hardness to 120–140 HV via Mg–Al–Zn intermetallic phases.
3. Production Process
Hot-Dipping Temperature: ~600°C ensures full alloy formation; lower temperatures reduce coating hardness by 10–15 HV.
Skin Passing: A light cold-rolling pass (1–3% reduction) increases hardness by 3–5 HRB and improves surface smoothness.
Cooling Rate: Rapid quenching forms a finer, harder coating microstructure (10–20 HV higher than slow cooling).
Hardness vs. Performance Tradeoffs
Galvalume's 50–65 HRB hardness is engineered for balanced performance:
Formability: ≤65 HRB enables bending, roll-forming, and deep drawing without cracking (critical for roofing, siding, and automotive panels).
Wear Resistance: 85–120 HV is ~2× harder than pure galvanized steel (55–65 HV), reducing scratching during transportation and installation.
Corrosion Resistance: Harder coatings (≥100 HV) have denser Al–Zn layers, extending salt spray resistance to 4,500+ hours (3–6× longer than galvanized steel).
Hardness Testing Methods
Industry standards specify three primary tests for galvalume hardness:
- Rockwell (HRB): Most common for coils/sheets; uses a 1/16-inch steel ball under 100 kg load (range: 50–65 HRB).
- Vickers (HV): Precision test for thin coatings; uses a diamond pyramid under 5–10 kg load (range: 85–120 HV).
- Brinell (HB): For thicker substrates; uses a 2.5 mm steel ball under 187.5 kg load (range: 70–100 HB).
Frequently Asked Questions (FAQ)
Q1: Is galvalume harder than galvanized steel?
A: Yes. Galvalume (85–120 HV) is ~2× harder than hot-dip galvanized steel (55–65 HV), due to its 55% aluminum alloy coating.
Q2: Can hardness be customized for specific applications?
A: Absolutely. We adjust substrate grade (CQ/DQ/S-series), coating thickness (AZ70–AZ275), and skin-pass reduction to target hardness (45–75 HRB) for forming, structural, or high-wear needs.
Q3: Does hardness affect corrosion resistance?
A: Yes. Harder galvalume (≥100 HV) has a denser Al–Zn–Si microstructure, improving barrier protection and extending salt spray life to 4,500+ hours.
Q4: What happens if hardness is too high?
A: Hardness >70 HRB reduces formability, increasing cracking risk during bending or deep drawing (common in ultra-high-strength G550 grades).
Q5: How is hardness controlled during production?
A: We monitor substrate hardness via inline HRB testers, control hot-dipping temperature (590–610°C), and adjust skin-pass pressure to maintain tolerance within ±3 HRB.
Galvalume steel coils offer a precision-tuned hardness range (50–65 HRB / 85–120 HV) that balances formability, wear resistance, and corrosion protection. At GNEE STEEL, we rigorously control substrate grade, coating parameters, and production processes to deliver consistent hardness for your application-whether you need ductile CQ/DQ grades for forming or high-strength S-series grades for structural use.
Need help selecting the right galvalume hardness for your project? Contact our technical team today for customized recommendations and product data sheets.
Galvalume steel grades and properties
| Grades | Yield strength/Mpa | Tensile strength/Mpa | Elongation at break/% |
| DX51D+AZ | ≤360 | ≤440 | 192PCS |
| DX52D+AZ | ≤260 | 300-360 | 180PCS |
| DX53D+AZ | ≤200 | 270-320 | 144PCS |
| DX54D+AZ | ≤180 | 270-310 | 108PCS |
| S250GD+AZ | ≥250 | ≥330 | 108PCS |
| S350GD+AZ | ≥350 | ≥420 | |
| S450GD+AZ | ≥450 | ≥510 | |
| S550GD+AZ | ≥550 | ≥560 | |
| LG550GD+AZ | ≥550 | ≥560 |
