Cyanide-free gold plating is an environmentally friendly surface treatment technology that replaces traditional cyanide plating solution to achieve gold plating (such as copper-zinc alloy, copper-tin-zinc alloy, etc.) on the surface of steel parts.
Author: Marisa
Cyanide-free gold plating is an environmentally friendly surface treatment technology that replaces traditional cyanide plating solution to achieve gold plating (such as copper-zinc alloy, copper-tin-zinc alloy, etc.) on the surface of steel parts.
The following are its key technologies, process steps and precautions:
1. Common systems for cyanide-free imitation gold electroplating
1. Pyrophosphate system
Plated solution composition:
Main salt: copper pyrophosphate + zinc pyrophosphate
Complexing agent: potassium pyrophosphate (K₄P₂O₇)
Additives: brightener (such as sodium thiosulfate), pH buffer
Features:
Environmentally friendly and non-toxic, the plating solution has good stability.
The pH (8.5~9.5) and temperature (40~50℃) need to be strictly controlled.
2. HEDP (hydroxyethylidene diphosphonic acid) system
Plated solution composition:
Main salt: Cu²⁺, Zn²⁺ (or Sn²⁺)
Complexing agent: HEDP (alternative to cyanide)
Auxiliary agent: sodium carbonate, brightener
Features:
The coating is finely crystallized and has strong bonding.
The pH range is wide (9~11) and the operation is simple.
3. Citrate system
Applicable coating: copper-zinc-tin ternary alloy imitation gold.
Advantages: wastewater is easy to treat, suitable for precision parts.
2. Cyanide-free imitation gold electroplating process
Pretreatment
Degreasing (alkaline or ultrasonic) → pickling (10% sulfuric acid) → activation (5% hydrochloric acid).
Pre-plating base layer (improving bonding strength)
Cyanide-free alkaline copper: such as pyrophosphate copper plating, thickness 1~2μm.
Cyanide-free nickel plating: optional (for parts with high corrosion resistance requirements).
Cyanide-free gold plating
Example of plating solution formula (HEDP system):
Copper sulfate (CuSO₄·5H₂O): 10~15 g/L
Zinc sulfate (ZnSO₄·7H₂O): 5~8 g/L
HEDP: 80~120 g/L
Sodium carbonate: 20~30 g/L (adjust pH to 10~11)
Brightener: trace (commercial additives such as AT-3)
Process parameters:
Temperature: 25~35℃
Current density: 0.5~1.5 A/dm²
Time: 1~3 minutes (thin layer) to 5~10 minutes (thick layer).
Post-treatment
Passivation: immersion in benzotriazole (BTA) solution (anti-discoloration).
Sealing protection: spray transparent epoxy resin or UV paint.