The metal surface will inevitably be oxidized during various heat treatment, mechanical processing, transportation and storage processes, resulting in an oxide layer of uneven thickness. At the same time, it is also susceptible to various oil pollution and adsorption of some other impurities.
Oil stains and some adsorbents, the thinner oxide layer can be cleaned with solvent, chemically treated and mechanically treated successively, or directly chemically treated. For heavily oxidized metal surfaces, if the oxide layer is thick, solvent cleaning and chemical treatment cannot be used directly, but mechanical treatment is best first.
Generally, the treated metal surface is highly active and is more likely to be polluted by dust and moisture again. For this reason, the treated metal surface should be glued as quickly as possible.
The storage period of metals after different treatments is as follows:
(1) Wet-blasted aluminum alloy, 72h;
(2) Chromic acid-sulfuric acid treated aluminum alloy, 6h;
(3) Anodized aluminum alloy, 30 days;
(4) Sulfuric acid treated stainless steel, 20 days;
(5) Sandblasted steel, 4h;
(6) Wet-blasted brass, 8h.
1. Surface treatment method of aluminum and aluminum alloy
[method 1]
Degreasing treatment. Wipe with absorbent cotton dampened with solvent. After removing the oil stains, wipe it several times with a clean cotton cloth. Commonly used solvents are: trichloroethylene, ethyl acetate, acetone, methyl ethyl ketone and gasoline.
[Method 2]
Chemical treatment in the following solution after degreasing:
Concentrated sulfuric acid 27.3 potassium dichromate 7.5 water 65.2
Soak at 60-65°C for 10-30 minutes, then take it out and rinse with water, dry or dry below 80°C; or wash in the following solution and then dry:
Phosphoric acid 10 n-butanol 3 水 20
This method is suitable for phenolic-nylon glue, etc., and the effect is good.
[Method 3]
Chemical treatment in the following solution after degreasing:
Ammonium bifluoride 3-3.5 chromium oxide 20-26 sodium phosphate 2-2.5 concentrated sulfuric acid 50-60 boric acid 0.4-0.6 water 1000
Soak at 25-40°C for 4.5-6min, then wash and dry. The bonding strength of this method is relatively high, and it is bonded within 4 hours after treatment, and is suitable for bonding epoxy glue and epoxy-nitrile glue.
[Method 4]
Chemical treatment in the following solution after degreasing:
Phosphoric acid 7.5 Chromium oxide 7.5 Alcohol 5.0 Formaldehyde (36-38%) 80
Soak at 15-30°C for 10-15min, then wash and dry at 60-80°C.
[Method 5]
After degreasing, anodize in the following solution:
Concentrated sulfuric acid 22g/l
Immerse for 10-15min under the direct current intensity of 1-1.5A/dm2, and then immerse in saturated potassium dichromate solution for 5-20min at 95-100°C
, Then wash and dry.
[Method 6]
Chemical treatment in the following solution after degreasing:
Potassium dichromate 66 sulphuric acid (96%) 666 water 1000
Soak for 10min at 70°C, then wash with water and dry.
[Method 7]
Chemical treatment in the following solution after degreasing:
Nitric acid (d=1.41) 3 Hydrofluoric acid (42%) 1
Immerse for 3s at 20°C, that is, rinse with cold water, then wash with hot water at 65°C, rinse with distilled water, and dry. This method is suitable for cast 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
Raise the voltage from 0 V to 10V within 10 minutes at 40°C, hold for 20 minutes, and then increase from 10V to 50V within 5 minutes, hold for 5 minutes
, Then wash with water and dry at 700C. Note: The concentration of free chromium oxide should not exceed 30-35g/l.
[Method 9]
Chemical treatment in the following solution after degreasing:
Sodium silicate 10 non-ionic detergent 0.1
Soak for 5min at 65°C, then wash with water below 65°C, then wash with distilled water and dry. Suitable for bonding aluminum foil.
[Method 10]
Chemical treatment in the following solution after degreasing:
Sodium fluoride 1 concentrated nitric acid 15 水 84
Immerse for 1 min at room temperature, wash with water and then treat in the following solution:
Concentrated sulfuric acid 30 Sodium dichromate 7.5 水 62.5
Soak for 1 min at room temperature, wash with water, and dry.
2. Surface treatment method of magnesium and magnesium alloy
[method 1]
Degreasing treatment. Common solvents are: trichloroethylene, acetone, ethyl acetate and methyl ethyl ketone, etc.
[Method 2]
After degreasing, immerse in the following solution at 70-75°C for 5 minutes:
Sodium hydroxide 12 水 100
Rinse with cold water, and then immerse in the following solution at 20°C for 5 minutes:
Chromium oxide 10 water 100 anhydrous sodium sulfate 2.8
Rinse with cold water, then distilled water, and dry at 40°C.
[Method 3]
After degreasing, immerse in a 6.3% sodium hydroxide solution at 70°C for 10 minutes. After washing with water, immerse in the following solution at 55°C for 5 minutes:
Chromium oxide 13.8 Calcium sulfate 1.2 Water 85
Wash with distilled water, then immerse in the following solution at 55°C for 3 minutes:
Chromium oxide 10 Sodium sulfate 0.5 Water 89.5
After washing with water, dry below 60°C.
[Method 4]
Immerse in the following solution for 3min at 20°C:
Chromium oxide 16.6 Sodium nitrate 20 glacial acetic acid 105 Water 100
Rinse with cold water, rinse 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, rinse with distilled water, and dry below 70°C.