Metal surface treatment method (on)

Metal surfaces are inevitably oxidized during heat treatment, mechanical processing, transportation, and storage, resulting in a thick layer of uneven oxide. At the same time, it is also vulnerable to various oil pollution and adsorption of some other impurities.

For oil and certain adsorbents, the thinner oxide layer may be washed with solvents, chemically and mechanically, or chemically treated directly. For heavily oxidized metal surfaces, the oxide layer is thick and cannot be directly cleaned with a solvent and chemically treated. It is better to perform mechanical treatment first.

The treated metal surface is highly active and is easily re-contaminated with dust, moisture, and the like. For this purpose, the treated metal surface should be glued as fast as possible.

The period of storage of the metal after different treatments is as follows:
(1) wet blasting aluminum alloy, 72h;
(2) chromic acid - sulfuric acid treated aluminum alloy, 6h;
(3) Anodized aluminum alloy for 30 days;
(4) Sulfuric acid treated stainless steel, 20 days;
(5) sandblasted steel, 4h;
(6) Wet blasted brass, 8h.

First, aluminum and aluminum alloy surface treatment method

[method 1]
Degreasing treatment. Wipe the solvent with cotton wool to wipe it off. After removing the oil, wipe it several times with a clean cotton cloth. Commonly used solvents are: trichloroethylene, ethyl acetate, acetone, butanone, and gasoline.

[Method 2]
After degreasing, chemical treatment in the following solution:
Concentrated sulfuric acid 27.3 Potassium dichromate 7.5 Water 65.2
After immersing for 10-30min at 60-65°C, rinse with water, dry or dry below 80°C; or wash in the following solution and then dry:
Phosphoric acid 10 n-butanol 3 water 20
This method is suitable for phenolic - nylon rubber, etc., with good results.

[Method 3]
After degreasing, chemical treatment in the following solution:
Ammonium hydrogen fluoride 3-3.5 Chromium oxide 20-26 Sodium phosphate 2-2.5 Concentrated sulfuric acid 50-60
The boric acid 0.4-0.6 water 1000 is impregnated at 25-40°C for 4.5-6 minutes, ie washed and dried. This method has high bonding strength and is glued within 4 hours after processing. It is suitable for bonding epoxy adhesive and epoxy-nitrile rubber.

[Method 4]
After degreasing, chemical treatment in the following solution:
Phosphoric acid 7.5 Chromium oxide 7.5 Alcohol 5.0 Formaldehyde (36-38%) 80
Immerse for 10-15min at 15-30°C, then wash and dry at 60-80°C.

[Method 5]
After degreasing, anodizing in the following solution:
Concentrated sulfuric acid 22g/l
Immerse for 10-15 min at a DC intensity of 1-1.5 A/dm2, then immerse in a saturated potassium dichromate solution at 95-100 °C for 5-20 min, then wash and dry.

[Method 6]
After degreasing, chemical treatment in the following solution:
Potassium dichromate 66 Sulfuric acid (96%) 666 Water 1000
Dip at 70°C for 10 min, then wash and dry.

[Method 7]
After degreasing, chemical treatment in the following solution:
Nitric acid (d=1.41) 3 Hydrofluoric acid (42%) 1
Immerse for 3s at 20°C, rinse with cold water, wash with hot water at 65°C, rinse with distilled water, and dry. This method is suitable for casting aluminum alloys with high copper content.

[Method 8]
After sandblasting or grinding, anodize in the following solution:
Chromium oxide 100 Sulfuric acid 0.2 Sodium chloride 0.2
The voltage was increased from 0 V to 10 V at 40 °C in 10 min, held for 20 min, then increased from 10 V to 50 V in 5 min, held for 5 min, then washed with water, and dried at 700 °C. Note: The free chromium oxide concentration must not exceed 30-35g/l.

[Method 9]
After degreasing, chemical treatment in the following solution:
Sodium silicate 10 Non-ionic detergent 0.1
Soaking at 65°C for 5 min, then washing below 65°C, washing with distilled water and drying. Suitable for adhesive bonding of aluminum foil.

[Method 10]
After degreasing, chemical treatment in the following solution:
Sodium fluoride 1 Concentrated nitric acid 15 Water 84
Immerse for 1 min at room temperature, wash with water and treat in the following solution:
Concentrated sulfuric acid 30 sodium dichromate 7.5 water 62.5
Dilute at room temperature for 1min, wash and dry.


Second, magnesium and magnesium alloy surface treatment method


[method 1]
Degreasing treatment. Commonly used solvents are: trichloroethylene, acetone, ethyl acetate and butanone.

[Method 2]
After degreased, immersed in the following solution at 70-75°C for 5 minutes:
Sodium hydroxide 12 water 100
Rinse with cold water and dip in the following solution at 20 °C for 5 min:
Chrome oxide 10 water 100 anhydrous sodium sulfate 2.8
Rinse with cold water, wash with distilled water, and dry at 40°C.

[Method 3]
After degreased, immersed in a 6.3% sodium hydroxide solution at 70°C for 10 minutes, washed with water, and then immersed in the following solution at 55°C for 5 minutes:
Chrome oxide 13.8 Calcium sulfate 1.2 Water 85
Wash with distilled water and dip in the following solution at 55 °C for 3 min:
Chromium oxide 10 Sodium sulfate 0.5 Water 89.5
After washing, dry below 60°C.

[Method 4]
Immerse for 3min at 20°C in the following solution:
Chromium oxide 16.6 Sodium nitrate 20 Glacial acetic acid 105 Water 100 Rinse with cold water, wash with distilled water, and dry below 40°C.

[Method 5]
Immerse in the following solution at 60-70°C for 3 minutes:
Sodium dichromate 10 Magnesium sulfate 5 Manganese sulfate 5 Water 80
Rinse with cold water, wash with distilled water, and dry below 70°C.

[Method 6]
After degreased, immersed in the following boiling solution for 20min:
Sodium dichromate 1.5 Ammonium sulfate 3 Ammonia water (d=0.88) 0.3 Water 93.7
Rinse with warm water, wash with distilled water, and dry.

[Method 7]
Anodicize in a 10% solution of ammonium hydrofluoride below 30°C to a current density of less than 0.45A/m2 (one electrode panel), alternating voltage 90-120V, then wash and dry.

[Method 8]
Anodizing in the following solution at 20-30 °C:
Potassium hydroxide 12 Aluminum 0.75 Potassium fluoride anhydrous 3.4 Sodium phosphate 3.4 Potassium permanganate 1.5 Water 80
AC voltage 85V, current density 1.1-1.4A/m2, then washed with cold distilled water and dried.

[Method 9]
After degreasing, wash at 5 °C for 5-15min at 70 °C:
Sodium hydroxide 23-34 water 400
Wash with cold water for 5 min, then dip for 5-15 min in the following solution, temperature 55 °C:
Chromium oxide 57-68 Calcium nitrate 5 Water 450
Wash with cold water for 2 min, then dip for 3-12 min in the following solution, temperature 55 °C:
Chromium oxide 45 Sodium phosphate 8 Water 450
Wash in cold water for 2 min, then dry at 40 °C for 30 min.