As an internationally recognized eco-friendly metal protection process, Dacromet surface treatment technology is gradually replacing traditional electrogalvanizing and hot-dip galvanizing processes, thanks to its unique advantages of hydrogen embrittlement resistance and high corrosion resistance. The following is a rigorous exposition of its technical characteristics, process advantages, and application specifications to ensure accuracy and clarity.
I. Core Technical Advantages of Dacromet Process (Precise Data and Industry Standards)
1. Ultra-Long-Acting Corrosion Resistance
Coating Characteristics: Using a zinc-chromium composite coating with a thickness of only 4–8μm, which bonds with the metal substrate through chemical bonds.
Corrosion Resistance Data: In accordance with GB/T 10125 standards, after 1,200 hours of neutral salt spray testing, no red rust appears. Its corrosion resistance is 7–10 times that of traditional electrogalvanizing (salt spray resistance: 100–300 hours).
Thread Compatibility: The coating evenly covers the thread profile, with the pitch diameter tolerance controlled to ISO 965-1 precision grade (e.g., M10 bolt pitch diameter: 6.912±0.03mm). No reaming is required to ensure a thread engagement torque pass rate ≥99%.
2. Zero Hydrogen Embrittlement Risk for High-Strength Applications
Process Principle: The entire process involves no acid pickling or electroplating (hydrogen evolution steps), using waterless electrophoretic coating technology to fundamentally prevent hydrogen atom penetration.
Application Range: Specifically suitable for high-strength bolts of grade 8.8 and above (e.g., 10.9, 12.9), addressing the complex process risks of traditional electrogalvanizing (pickling → electroplating → dehydrogenation), where incomplete dehydrogenation can cause delayed fracture.
3. High-Temperature Resistance and Surface Performance
Temperature Adaptability: The coating can withstand long-term use at 300°C (short-term tolerance up to 350°C) without oxidation or peeling.
Surface Quality: Surface roughness Ra≤3.2μm, adhesion reaching ISO 2409 cross-cut test grade 0 (no peeling in 1mm grid spacing), supporting coloring treatments such as black or silver-gray.
4. Environmental Friendliness and Process Economy
Eco-Friendliness: The entire process is free of wastewater or exhaust emissions, compliant with EU RoHS and REACH regulations, eliminating the wastewater treatment costs of traditional galvanizing (approximately ¥8–15 per ton of wastewater).
Mixed-Line Production: Capable of processing grade 4.8 low-carbon steel and grade 12.9 alloy steel on the same line, saving equipment investment and process changeover time (traditional processes require separate lines).
5. Precision Part Anti-Corrosion Solutions
Dimensional Assurance: Complex structural parts such as hex socket head cap screws maintain unchanged dimensions after treatment (e.g., M6 hexagon across flats: 10±0.1mm), solving assembly interference caused by thick hot-dip galvanized coatings (50–80μm).
Small-Specification Adaptability: Suitable for small specifications (M2.5–M8), with 1,000-hour salt spray testing showing no corrosion, replacing the anti-corrosion challenges of thin-walled parts that cannot be hot-dip galvanized.
II. Comparison with Traditional Surface Treatment Processes (Quantitative Table)
| Performance Indicator | Dacromet Treatment | Electrogalvanizing | Hot-Dip Galvanizing |
|---|---|---|---|
| Coating Thickness | 4–8μm | 8–15μm | 50–80μm |
| Salt Spray Resistance (no red rust) | ≥1,200h | 100–300h | 500–800h |
| Hydrogen Embrittlement Risk | None | High (requires dehydrogenation) | Medium (cooling control needed) |
| High-Temperature Resistance | 300°C long-term | ≤100°C | ≤200°C |
| Environmental Compliance | No pollutant emissions | Requires zinc-containing wastewater treatment | Requires zinc slag wastewater treatment |
| Thread Fit Cost | Standard tolerance (0 cost) | Possible rework | Mandatory reaming (+5% cost) |
III. Professional Application Scenarios in Heavy-Duty Automotive Industry
1. Safety Protection for High-Strength Critical Bolts
Application Parts: Chassis suspension systems (leaf spring bolts, shock absorber bolts), engine block connections (cylinder head bolts, flywheel bolts).
Case Data: After a heavy truck enterprise replaced grade 10.9 electrogalvanized bolts with Dacromet-treated ones, hydrogen embrittlement fractures dropped from 12 cases annually to zero, and salt spray test life increased from 300 hours to 1,500 hours.
2. Interior Parts with Dual Aesthetic and Performance Requirements
Application Parts: Cab seat fixing bolts, dashboard bracket bolts, door hinge bolts.
Process Value: Uniform metallic luster (Ra≤1.6μm), salt spray test ≥800 hours, meeting the "aesthetics + long-term anti-corrosion" needs of passenger vehicle interior parts (traditional hot-dip galvanizing has a rough surface, Ra≥6.3μm).
3. Precision Assembly Requirements for New Energy Vehicles
Application Scenarios: Battery pack fasteners (M6–M10 hex socket head cap screws), motor housing connection bolts.
Technical Advantages: Thin coating (4–6μm), high precision (across flats tolerance ±0.05mm), adapting to the precise positioning requirements of automated assembly equipment and avoiding bolt hole matching errors caused by thick hot-dip galvanized coatings (errors ≥0.2mm may lead to robot assembly failures).
IV. Process Control Key Points and Quality Acceptance Standards
Coating Thickness Inspection:
Using a coulometric thickness gauge (ISO 2177 standard), sampling 5% of parts per batch, with thread root thickness ≥4μm and planar area thickness 4–8μm.
Adhesion Verification:
Performing cross-cut tests (1mm spacing, 10×10 grid), with ISO 2409 standard grade 0 (no peeling) as qualified; grade 1 (peeling area ≤5%) requiring rework.
High-Temperature Stability Test:
Placing samples in a 300°C constant-temperature oven for 2 hours; after cooling, inspecting for no blistering or peeling, with thread go-gauge pass rate reaching 100%.
V. Clarifications on Common Industry Misunderstandings (Correcting Cognitive Biases)
Misunderstanding 1: "Reaming is mandatory after Dacromet treatment for assembly"
Clarification: Coating thickness (4–8μm) is far smaller than thread tolerance zones (e.g., M10 thread pitch diameter tolerance ±0.125mm), requiring no reaming for standard fits. Test data shows that the difference in tightening torque between Dacromet bolts and ordinary bolts is ≤8% (GB/T 16823.1 standard allows ±15% variation).
Misunderstanding 2: "Dacromet is only suitable for high-strength bolts; ordinary bolts don't need it"
Clarification: Grade 4.8 ordinary bolts are equally suitable and can be produced on the same line as high-strength bolts. For example, an automotive parts factory unified Dacromet treatment for standard parts (grade 4.8) and structural parts (grade 10.9), reducing production costs by 18% and improving inventory management efficiency by 30%.
Misunderstanding 3: "Small hex socket head cap screws become stuck in wrenches after Dacromet treatment"
Clarification: The Dacromet process imposes no restrictions on geometry. M3 hex socket head cap screws achieve ±0.03mm across flats precision after treatment (ISO 262 standard requires ±0.05mm), fitting standard hex wrenches, with measured assembly efficiency identical to untreated parts.
Conclusion
Through a combination of materials science and process innovation, Dacromet treatment technology addresses the bottlenecks of traditional galvanizing processes in high-strength applications, precision assembly, and environmental compliance. When applying this technology, enterprises should focus on coating thickness control, adhesion testing, and high-temperature process parameters while discarding misunderstandings like "mandatory reaming" or "strength grade limitations" to fully leverage its dual advantages of product reliability enhancement and comprehensive cost reduction. The popularization of this technology is not only a choice for process upgrading but also a significant symbol of the manufacturing industry's transformation toward green and high-end development.
