Dacromet Flange Bolts: A Comprehensive Introduction to High-Performance Anti-Corrosion Fasteners 

2. What Is Dacromet Coating?

Dacromet is a high-performance zinc-aluminum flake coating system developed as an advanced alternative to traditional electroplating and hot-dip galvanizing. The coating consists of overlapping layers of zinc and aluminum flakes suspended in an inorganic binder. After application by dip-spin, spray, or dip-drain methods and high-temperature curing, the flakes form a dense, multi-layered barrier that provides multiple mechanisms of anti-corrosion protection.

Unlike conventional zinc plating that relies on a single continuous metallic layer, the lamellar structure of zinc and aluminum flakes creates a complex pathway that significantly slows penetration of water, oxygen, and chloride ions. This unique microstructure forms the foundation of the coating’s superior corrosion resistance and long-lasting rust prevention capability. Typical Dacromet coating thickness ranges from 5 to 12 micrometers (μm). Despite its thin profile, a properly applied Dacromet layer can achieve salt spray resistance exceeding 1,000 hours—and often over 2,000 hours—without red rust appearance. This level of anti-rust performance far surpasses conventional electro-galvanized coatings and frequently outperforms hot-dip galvanizing in cyclic and long-term exposure tests.

3. Key Advantages of Dacromet Flange Bolts

Dacromet flange bolts combine mechanical reliability with superior anti-corrosion durability, making them ideal for high-strength and critical fastening applications.

3.1 Outstanding Corrosion Resistance and Anti-Rust Performance

The primary reason for selecting Dacromet-coated flange bolts is their exceptional corrosion resistance. Independent salt spray tests (ASTM B117 / ISO 9227) consistently show that Dacromet coatings withstand 1,000 to 2,000 hours or more before red rust appears. Comparative evaluations demonstrate that Dacromet often provides 3 to 10 times better anti-rust performance than standard zinc electroplating. This superior rust prevention capability translates into significantly extended service life for flange connections exposed to aggressive environments such as coastal, marine, and industrial atmospheres.

3.2 No Risk of Hydrogen Embrittlement

High-strength flange bolts (grades 8.8, 10.9, 12.9 and ASTM A490 / F3125 structural bolts) are particularly sensitive to hydrogen embrittlement. Traditional electroplating involves acidic pickling and electrolytic deposition that can introduce hydrogen into the steel, risking delayed brittle fracture. Dacromet is a non-electrolytic process that avoids this risk, making Dacromet-treated bolts the preferred anti-corrosion solution for high-tensile flange bolts.

3.3 Thin Coating with Excellent Thread Compatibility

With a typical thickness of only 5–12 μm, the Dacromet film does not significantly alter thread dimensions or interfere with nut engagement. In contrast, hot-dip galvanizing often produces thick, uneven coatings that fill threads and require oversized nuts. Dacromet flange bolts can therefore be assembled with standard nuts while still delivering outstanding corrosion resistance and anti-rust protection.

3.4 High-Temperature Stability and Multi-Mechanism Protection

Dacromet coatings maintain their anti-corrosion integrity at elevated temperatures (typically up to 250–300 °C), which is valuable for flange bolts near engines, exhaust systems, or outdoor structures. The coating provides four complementary rust prevention mechanisms: (1) Barrier protection from overlapping zinc-aluminum flakes; (2) Galvanic sacrificial protection by zinc; (3) Self-repairing effect through oxide filling of minor damages; and (4) Passivation by the inorganic binder that retards further corrosion progression.