ELECTRONIC SURFACE TREATMENT MATERIAL SUPPLIER

Core Functions

1. Alkaline cleaning: Eliminate drawing oil, cutting fluid, grease, fingerprints, polishing compound and surface dirt. Uniformly remove partial native aluminium oxide layer to expose fresh homogeneous alloy substrate. Poor cleaning leads to patchy passivation film, blistering or coating delamination.

1. Acid desmutting / deoxidising: Dissolve residual alkaline smut, heavy‑metal intermetallic precipitates and mixed oxide residues left after alkaline etching. Produce a consistent micro‑uniform surface ready for passivation.

1. Passivation (conversion treatment): Deposit a thin, adherent inorganic protective film over active aluminium surface. The film blocks atmospheric corrosion pathways, improves salt‑spray performance, and serves as an excellent bonding base for paints, adhesives and electroplated underlayers.

Typical Bath Formulations

• Sodium hydroxide / potassium hydroxide: 10–35 g/L (provides mild etching capability)

• Sodium carbonate / sodium bicarbonate: 20–50 g/L (pH buffering, alkalinity reserve)

• Sodium phosphate / polyphosphates: 5–15 g/L (sequestering agent for hard‑water ions)

• Organic surfactants (non‑ionic + anionic wetter): 1–4 g/L (oil emulsification, surface wetting)

• Inhibitor additives: trace organic inhibitors (prevent over‑etching on sensitive aluminium alloys)

• Operating parameters: pH 10.5‑12.5; temperature 40–60 °C; immersion time 2–8 min; air agitation preferred.

Two mainstream types:
Type A – Nitric‑based desmut (traditional)

• Nitric acid (HNO₃): 80–150 mL/L

• Sulfuric acid (H₂SO₄): 30–70 mL/L

• Water: balance

• Operating: ambient‑45 °C, 1–5 min. Efficient for removing copper‑rich smut from die‑cast aluminium.

Type B – Nitric‑free desmut (eco‑friendly modern grade)

• Sulfuric acid: 50‑120 mL/L

• Organic complexing agents, ferric / persulfate oxidisers: proprietary dosage

• Corrosion moderators

• Operating: 30‑50 °C, 2‑6 min. Low NOₓ emission for environmental compliance.

Option 1: Chromate‑based passivation (yellow iridescent film, traditional)

• Chromic anhydride (CrO₃): 20‑50 g/L

• Sodium dichromate: 10‑30 g/L

• Sulfuric acid / nitric acid: trace for pH adjustment

• pH range: 1.5‑2.5

• Produces golden‑yellow chromate conversion film; outstanding corrosion resistance. Restricted in many regions due to hexavalent chromium regulation.

Option 2: Chromate‑free Zirconium‑titanium passivation (modern industry standard)

• Zirconium salt (hexafluorozirconate): 3‑10 g/L (main film‑forming component)

• Titanium compound / silane additive: 0.5‑3 g/L (modifies film compactness)

• Fluoride source: controlled low dosage (dissolves native Al₂O₃ to initiate film growth)

• pH adjustor (nitric acid / ammonia): maintain pH 3.8‑4.8

• Wetting agent: trace non‑ionic surfactant

• Operating temperature: 30‑50 °C; immersion time 1‑4 min. Forms thin, transparent to light‑blue conversion layer; RoHS compliant, widely used before painting and powder coating.