Electro galvanizing is a common surface finish for self-drilling screws, complying with DIN EN ISO 2081. The process includes several controlled stages to guarantee corrosion resistance while maintaining good drilling performance.

1. Degreasing Screws are soaked in heated alkaline tanks with agitation to remove cold-forging lubricants. Residual grease leads to uneven zinc coating and peeling. Full water rinsing after degreasing is necessary to wash away alkaline liquid.

2. Pickling and rinsing Dilute acid removes surface rust and oxide scale. Operators must strictly limit pickling time. Over-pickling causes hydrogen embrittlement, which may crack hardened drill tips under load. Complete rinsing prevents acid from contaminating subsequent baths.

3. Activation Brief acid activation eliminates thin passive oxide films on steel surfaces, ensuring strong adhesion between zinc and the base metal, followed by clean rinsing.

4. Zinc electroplating Screws are barrel-plated. Current density and plating time are adjusted to achieve 5–12 μm zinc thickness. A thin coating offers insufficient rust protection. Excess zinc fills threads and blunts drill points, making screws fail to drill metal sheets at construction sites. Continuous bath filtration reduces surface flaws.

5. Passivation Blue-white passivation is widely used to boost salt spray resistance. Operators control passivation time to avoid irregular discoloration.

6. Sealing (optional) Sealing closes micro-pores in the passivation layer for longer anti-corrosion life. Final rinsing and drying finish the whole process.

Key requirements under DIN EN ISO 2081: Hydrogen baking is required for high-hardness self-drilling screws to reduce embrittlement. Each batch needs sampling tests for coating thickness, salt spray performance and adhesion. Visual inspection focuses on threads and drill tips, checking for bare areas, bubbles or peeling.

Electro galvanized screws have a bright appearance. The zinc layer serves as a sacrificial anode to protect steel. They fit indoor steel frames and sheltered outdoor projects, but are not recommended for coastal high-salt environments. Tight process control avoids rust complaints and ensures stable drilling performance.