Hard chromium plating process on deformed aluminum alloy

1. Process flow

Gasoline or trichloroethylene degreasingâ†’dryingâ†’dryingâ†’coolingâ†’upper fixtureâ†’weak alkali corrosionâ†’warm water washâ†’rinse in running waterâ†’nitric acid soakingâ†’washing in waterâ†’rinse in flowing waterâ†’immersion zincâ†’galvanizationâ†’rinse in water â†’ Wash with water â†’ Chrome plating â†’ Wash in the recovery tank â†’ Wash â†’ Lower fixture â†’ Wash â†’ Wash with hot water â†’ Dry â†’ Cool â†’ Self-test.

2. The main recipe and process conditions of the pretreatment

(1) Weak alkali corrosion

Trisodium phosphate (Na3PO4) 25~30g/L

Sodium carbonate (Na2CO3) 25~30g/L

Additive 2~4g/L

OP-10 emulsifier 0.5~1ml/L

T75~85Â°C

T40~60s

(2) acid etching solution

Nitric acid (HNO3) 400~500ml/L

Excess water

T room temperature

T30~60s

3. Zinc dipping solution formulation and process conditions

Zinc Oxide (ZnO) 55~60g/L

Sodium hydroxide (NaOH) 300~325g/L

Ferric chloride (FeCl3Â·6H2O) 1.0~1.2g/L

Potassium sodium tartrate (KNaC4H4O6Â·4H2O) 40~50g/L

Sodium nitrate 0.5~1g/L

T30~37Â°C

T40~60s

Note: After the aluminum parts are galvanized, electroplating is performed in the solution with a current of 0.8~1.2 A/dm2. For a time of 1~2 min, the best results are obtained.

4. Hard chromium plating solution formulation and process conditions

Chromate (CrO3) 250~260g/L

Sulfuric acid (H2SO4:d=1.84)2.5~2.6g/L

Trivalent chromium (Cr2O3) 2~4g/L

CrO3: SO42-100: 0.9~1.05

T52Â°C

DK25~35A/dm2

V6~8V

t depending on the thickness needs

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