At China Aluminum Network, the surface treatment process for aluminum parts involves several key steps to ensure high-quality plating results. The procedure starts with degreasing using either gasoline or trichloroethylene, followed by drying and cooling. Next, the parts are placed on a fixture, then subjected to weak alkali corrosion. Afterward, they undergo warm water washing, followed by rinsing in running water, and immersion in nitric acid. A thorough cleaning in clean water is performed before another rinse in running water. Then comes zinc immersion, zinc plating, and multiple rinses with running water and regular water. Finally, hard chrome plating is applied, followed by rinsing in the recovery tank, additional washing, and removal from the lower jig. The process concludes with hot water rinsing, drying, cooling, and a self-test to ensure quality.
The pretreatment stage includes two main solutions: a weak alkali corrosion bath composed of trisodium phosphate (Na₃PO₄) at 25–30 g/L, sodium carbonate (Na₂CO₃) at 25–30 g/L, and an additive at 2–4 g/L. It also contains 0.5–1 ml/L of OP-10 emulsifier. The temperature is maintained between 75–85°C, and the treatment time is 40–60 seconds. For acid etching, the solution consists of nitric acid (HNO₃) at 400–500 ml/L with water as the balance. The process occurs at room temperature for 30–60 seconds.
The zinc dipping solution includes zinc oxide (ZnO) at 55–60 g/L, sodium hydroxide (NaOH) at 300–325 g/L, ferric chloride (FeCl₃·6H₂O) at 1.0–1.2 g/L, potassium sodium tartrate (KNaC₄H₄O₆·4H₂O) at 40–50 g/L, and sodium nitrate at 0.5–1 g/L. The temperature is kept between 30–37°C, and the immersion time is 40–60 seconds. After zinc immersion, electroplating is carried out at a current density of 0.8–1.2 A/dm² for 1–2 minutes for optimal results.
For hard chromium plating, the solution contains chromic acid (CrO₃) at 250–260 g/L, sulfuric acid (H₂SO₄, d=1.84) at 2.5–2.6 g/L, and trivalent chromium (Cr₂O₃) at 2–4 g/L. The ratio of CrO₃ to SO₄²⻠should be around 100:0.9–1.05. The operating temperature is set at 52°C, with a current density of 25–35 A/dm² and a voltage of 6–8 V. The plating time varies depending on the required thickness.
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