When selecting a surface treatment for fasteners, consider the following:

1. Environment: Dry indoor conditions → electro-galvanizing or black oxide; humid outdoor conditions → hot-dip galvanizing or thermal diffusion galvanizing (zinc diffusion); high salt-spray environments, automotive, or chemical industries → zinc-nickel alloy or Dacromet/zinc-aluminum coatings.

2. Strength and hydrogen embrittlement: Electro-galvanizing is suitable for strength grades below 8.8; for grades 10.9 and above, avoid acid pickling and electroplating—prefer Dacromet, mechanical galvanizing, or zinc-aluminum coatings; if electroplating is used, a de-hydrogenation process is mandatory.

3. Threads and assembly: Hot-dip galvanized coatings are thick, requiring tolerance allowances or post-plating thread tapping; if torque specifications apply, clearly define the friction coefficient and lubrication requirements.

4. Application and cost: Preparation for painting → phosphating; stainless steel → passivation; decorative/wear-resistant → chrome or nickel plating.

Time：10/10/2026 16:40:20

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