Zinc plating

Electrolytically deposited zinc coating, with a thickness of 5-20μm, features good uniformity, a fine appearance, and moderate corrosion resistance (salt spray resistance for 24-96 hours).

Small precision parts (such as precision gears, electronic hardware parts), parts with complex structures (grooves, small holes), and parts requiring a fine appearance.

Low-carbon steel, medium-carbon steel, alloy steel, and some stainless steels (special activation required)

Requirements:

· Degreasing (ultrasonic / chemical degreasing, to remove cutting oil and anti-rust oil)

· Rust removal (acid washing, to remove oxide scale and rust)

· Activation (weak acid washing, to enhance the adhesion of the coating)

Hot-dip galvanizing

Immersed in molten zinc liquid (440-460℃), a zinc-iron alloy layer is formed with a thickness of 50-200μm and strong corrosion resistance (salt spray resistance for 500-2000 hours).

Large structural parts (brackets, frames), heavy machinery accessories (bearing blocks, flanges), welded special-shaped parts, and outdoor-use parts.

Low-carbon steel, low-alloy steel, cast iron (pretreatment is required to avoid embrittlement)

Requirements:

· Degreasing (high-temperature degreasing or alkaline cleaning)

· Rust removal (acid washing or sandblasting, thoroughly removing oxide scale, especially at weld seams)

· Pre-dip (immersion in pre-dip agent to prevent secondary oxidation and ensure adhesion of the coating)

Zinc-nickel alloy coating

Electroplating deposition of zinc-nickel alloy (with a nickel content of 8-15%), with a thickness of 8-15μm and excellent corrosion resistance (salt spray resistance for 500-1000 hours).

Parts requiring high corrosion resistance (special-shaped parts of automobile chassis, marine engineering accessories), and parts for low-temperature working conditions (-50℃ environment)

Low-carbon steel, medium-carbon steel, alloy steel

Required:

· Degreasing (precise degreasing to avoid oil contamination affecting the uniformity of alloy composition)

· Rust removal (light acid washing to prevent excessive corrosion)

· Activation (use of special activation solution to enhance the bonding strength between zinc and nickel)

Mechanical galvanizing

Mechanical collision cold-welded zinc powder, no electrolysis process, thickness 5-50μm, no risk of hydrogen embrittlement, and moderate corrosion resistance (salt spray resistance for 48-120 hours).

Brittle material parts (special-shaped cast iron parts), parts susceptible to hydrogen embrittlement (high-strength bolts, spring-type non-standard parts), and small irregular parts.

Cast iron, high-carbon steel, medium-carbon steel, and some powder metallurgy parts

Required:

· Degreasing (using solvent cleaning or alkaline degreasing to avoid oil contamination affecting the adhesion of zinc powder)

· Rust removal (using mild sandblasting or acid washing to remove loose rust, while maintaining the roughness of the substrate to enhance the bonding strength)

Note:

Pretreatment is a crucial step to ensure the quality of galvanizing. For all processes, the pretreatment duration and chemical concentration need to be adjusted according to the degree of oil contamination and rust on non-standard parts.

Special materials (such as stainless steel and high-alloy steel) need to add an "activation" step (e.g., electrolytic activation) after conventional pretreatment to break the surface passivation film and ensure coating adhesion.

For non-standard parts with deep holes or blind holes, the pretreatment process needs to include "ultrasonic cleaning" or "high-pressure spraying" to prevent missing plating caused by residual impurities in the holes.

Matching of batch size and process:

For small precision parts, choose electrolytic galvanizing (the larger the batch, the lower the unit cost);

Large outdoor parts should be hot-dip galvanized (with a large one-time investment but a long corrosion-resistant service life and low comprehensive cost);

For parts requiring high corrosion resistance, zinc-nickel alloy is selected (although the cost is high, it can reduce later maintenance costs).