Fastener Surface Treatments & Application Matching

Surface treatment improves fastener corrosion resistance, wear resistance and assembling performance, categorized into conventional anti-corrosion coating, high-end coating and functional coating. Process selection depends on corrosive environment, load condition and cost budget.

 

 

Cost-effective and technically mature, including black oxide, zinc plating and phosphating. Black oxide forms Fe₃O₄ film via chemical oxidation at only RMB 0.05 per piece, suited for indoor dry machinery such as machine guard bolts with merely 24-hour salt spray resistance and rust within one month outdoors. Zinc plating splits into electro-galvanizing and hot-dip galvanizing. Electro-galvanized layer is 5–10μm thick with 72–120h salt spray lifespan for home appliances and indoor pipelines at RMB 0.1–0.3 apiece. Hot-dip galvanizing features 50–100μm coating and over 500h salt spray endurance, ideal for outdoor steel structures like highway guardrail bolts; it costs twice as much as electroplating with possible zinc residue contamination. Phosphating produces phosphate film with poor standalone anti-corrosion performance and requires supplementary oil coating, mainly applied to auto engine bolts for enhanced lubricant adhesion.

 

 

Represented by Dacromet and nano-ceramic coating. Dacromet consists of zinc and aluminum powder for compact protective film, delivering 2000–5000h salt spray resistance (7–10 times conventional zinc coating) and zero hydrogen embrittlement, perfect for high-tensile fasteners. Yingxing Environmental’s Dacromet bolts were mass-adopted for offshore wind turbines at 2025 Shanghai Exhibition at RMB 1.2 per unit, 40% cheaper than imported equivalents. PVD AlCrN nano-ceramic coating withstands over 500℃ and 5000-hour salt spray. BASF’s products equip Tesla motor bolts against high-temperature corrosion at RMB 5 apiece for premium applications only.

 

 

Electrophoretic coating generates uniform multicolor paint film for decorative & anti-corrosion fasteners on furniture and automotive exterior parts. Hard chrome plating reaches HV800+ hardness with outstanding wear resistance for mold locating pins yet bears hexavalent chromium contamination restricted by EU regulations. Stainless steel passivation builds protective oxide film; passivated 316L lifts salt spray rating from 1000h to 1500h for medical device fasteners.

 

 

Avoid over-specification (e.g., unnecessary Dacromet for indoor cabinet bolts causing triple cost waste) and neglected hydrogen embrittlement (untempered electroplated high-strength bolts prone to delayed fracture). Grade-based selection: black oxide / electro-galvanizing for mild indoor dry corrosion; hot-dip galvanizing / oiled phosphating for damp industrial atmosphere; Dacromet / nano-ceramic coating for severe marine & chemical corrosion. A 2025 Haiyan policy offers 20% equipment subsidy for eco-friendly finishing, lifting Dacromet penetration from 35% to 60%.