►Electroplating thickness
Decorative electroplating
1. Normal thickness: 0.5μm～3μm
- Thin coating (0.5～1.5μm): for low-cost, fast-production light decoration (such as champagne gold, rose gold).
- Standard coating (1.5～3μm): takes into account both gloss and durability, suitable for high-end makeup brushes.
Functional electroplating
- Anti-corrosion coating (such as nickel base): 3~8μm, to enhance the corrosion resistance of aluminum substrate.
- Wear-resistant coating (such as hard chrome): 5~15μm, used in high wear areas (need to be combined with anodizing pretreatment).
►Electroplating process
Pretreatment (key step, affecting bonding strength)
- Degreasing: Alkaline solution is used to clean the oil stains on the surface of the aluminum tube.
- Acid pickling and activation: Dilute sulfuric acid or phosphoric acid removes the oxide film to expose the fresh aluminum surface.
- Zinc treatment (optional): Replace a layer of zinc on the aluminum surface to enhance the adhesion of subsequent coatings.
- Chemical nickel plating (optional): Non-electrolytic deposition of a 1-2μm nickel layer as a base for electroplating.
- Hanging plating: Aluminum tubes are hung in the electroplating tank, suitable for single-piece high-precision plating (such as gradient electroplating).
- Roller plating: Small batches of parts are placed in a drum for electroplating, with high efficiency but slightly lower uniformity.
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Multi-layer electroplating (such as "nickel + chromium"):
- Base nickel: 3~5μm (anti-corrosion, improve bonding strength).
- Surface chromium/gold: 0.5~2μm (decorative, anti-discoloration).
- Passivation: Chromate seals the pores of the coating and enhances corrosion resistance.
- Protective paint: UV varnish or transparent resin (optional, to improve wear resistance).
- Current density: 0.5～3 A/dm², too high will cause rough coating and burnt coating
- solution temperature:40～60℃(nickel plating solution), constant temperature control is required
- Electroplating time:1～10 minutes(depending on thickness requirements),time is positively correlated with thickness
- pH value:Nickel plating solution:4.0～4.8, too strong acidity will corrode aluminum substrate
►Testing methods and standards
Thickness
X-ray fluorescence (XRF): non-destructive, accuracy ±0.1μm.
Metallographic sectioning: destructive testing, highest accuracy (for arbitration)
Adhesion test
Scratch test: blade scratches, then tear tape, the coating does not fall off.
Thermal shock test: baking at 150℃ and then cooling suddenly, the coating does not crack.
Corrosion resistance
Salt spray test: No rust in neutral salt spray for 48 hours (ASTM B117)。
►Environmental protection and cost control
Environmental requirements
- RoHS compliance: Hexavalent chromium is prohibited (trivalent chromium process is required).
- Wastewater treatment: Wastewater containing nickel and chromium must be recycled separately to avoid heavy metal pollution.
- For every 1μm increase in plating thickness, the cost increases by about 15% to 20%.
- Multilayer electroplating (such as nickel + gold) is 30% to 50% more expensive than single-layer processes.
Alternative processes:
- PVD vacuum plating: no pollution, more uniform coating (thickness 0.1-2μm), but high equipment cost.
- Aqueous electroplating: environmentally friendly electroplating solution gradually replaces traditional cyanide system.
- Gradient color plating: achieved through mask or current density gradient.
- Matte plating: adding matting agent to the plating solution or post-processing sandblasting.
The exact process parameters can be adjusted according to specific requirements (such as coating color, wear resistance level).
