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Surface Phosphating Treatment Method
During various processes such as heat treatment, machining, transportation, and storage, the metal surface is inevitably exposed to oxidation, resulting in a thick and uneven oxide layer. In addition, it may be contaminated with oils and other impurities. For lighter oil stains and certain adsorbates, a thin oxide layer can be treated using solvent cleaning, chemical treatment, or mechanical methods. However, for heavily oxidized surfaces where the oxide layer is thick, mechanical treatment is usually necessary before applying any chemical treatment. After processing, the metal surface becomes highly reactive and prone to recontamination from dust, moisture, and other environmental factors. Therefore, it's important to bond the metal as soon as possible after surface preparation.
The recommended storage period for processed metals varies depending on the type of material and treatment method:
(1) Aluminum alloy after wet blasting – 72 hours;
(2) Steel after sandblasting – 4 hours;
(3) Anodized aluminum alloy – 30 days;
(4) Stainless steel treated with sulfuric acid – 20 days;
(5) Aluminum alloy treated with chromic acid-sulfuric acid – 6 hours;
(6) Brass after wet blasting – 8 hours.
Surface Phosphating Treatment Methods
Surface Preparation Methods for Aluminum and Aluminum Alloys
[Method 1] After degreasing, immerse the metal in the following solution at 60–65°C for 10–30 minutes:
Concentrated sulfuric acid 27.3%, potassium dichromate 7.5%, water 65.2%.
Rinse with water, dry, or dry below 80°C. Alternatively, rinse in the following solution:
Phosphoric acid 10%, n-butanol 3%, water 20%. This method is suitable for bonding with phenolic-nylon adhesives.
[Method 2] Perform degreasing by wiping with a damp cloth soaked in a solvent such as trichloroethylene, ethyl acetate, methyl ethyl ketone, or gasoline.
[Method 3] After degreasing, treat the surface in the following solution at 15–30°C for 10–15 minutes:
Phosphoric acid 7.5%, chromium oxide 7.5%, alcohol 5%, formaldehyde (36–38%) 80%. Then rinse at 60–80°C and dry.
[Method 4] After degreasing, anodize in the following solution:
Concentrated sulfuric acid 22g/L. Apply direct current at 1–1.5 A/dm² for 10–15 minutes, then immerse in a saturated potassium dichromate solution at 95–100°C for 5–20 minutes. Rinse with water and dry.
[Method 5] After degreasing, treat in the following solution at 25–40°C for 4.5–6 minutes:
Ammonium hydrogen fluoride 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. Rinse with water and dry. This method provides high bonding strength and should be bonded within 4 hours. It is ideal for epoxy and epoxy-butyronitrile adhesives.
[Method 6] After degreasing, immerse in the following solution at 65°C for 5 minutes:
Sodium silicate 10%, non-ionic detergent 0.1%. Rinse at 65°C or lower, then rinse with distilled water and dry. Suitable for bonding aluminum foil.
[Method 7] After sandblasting or sanding, anodize in the following solution:
Chromium oxide 100g/L, sulfuric acid 0.2g/L, sodium chloride 0.2g/L. Increase voltage from 0V to 10V at 40°C over 10 minutes, hold for 20 minutes, then increase to 50V in 5 minutes, hold for 5 minutes. Rinse with water and dry at 70°C. Note: Free chromium oxide concentration should not exceed 30–35g/L.
[Method 8] After degreasing, immerse in the following solution at room temperature for 1 minute:
Sodium fluoride 1%, concentrated nitric acid 15%, water 84%. Rinse with water, then immerse in the following solution:
Concentrated sulfuric acid 30%, sodium dichromate 7.5%, water 62.5%. Immerse for 1 minute at room temperature, rinse with water, and dry.
Surface Phosphating Treatment Methods
Surface Preparation Methods for Magnesium and Magnesium Alloys
[Method 1] After degreasing, immerse in the following solution at 70–75°C for 5 minutes:
Sodium hydroxide 12%, water 100%. Rinse with cold water, 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, wash with distilled water, and dry at 40°C.
[Method 2] Use solvents like trichloroethylene, ethyl acetate, and methyl ethyl ketone for degreasing.
[Method 3] Dip in the following solution at 20°C for 3 minutes:
Chromium oxide 16.6%, sodium nitrate 20%, glacial acetic acid 105%, water 100%. Rinse with cold water, wash with distilled water, and dry at 40°C or below.
[Method 4] After degreasing, immerse in a 6.3% sodium hydroxide solution at 70°C for 10 minutes, then wash with water. Next, 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%. Rinse with water and dry below 60°C.
[Method 5] Immersion 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 at 70°C or below.
[Method 6] Anodize at a current density of less than 0.45 A/m² in a 10% ammonium hydrogen fluoride solution at 30°C or lower, with a voltage of 90–120 V. Rinse with water and dry.
[Method 7] After degreasing, soak in the following lye at 70°C for 5–15 minutes:
Sodium hydroxide 23–34%, water 400%. Rinse with cold water for 5 minutes, then immerse in the following solution for 5–15 minutes at 55°C:
Chromium oxide 57–68%, calcium nitrate 5%, water 450%. Rinse with cold water for 2 minutes, then immerse in the following solution for 3–12 minutes at 55°C:
Chromium oxide 45%, sodium phosphate 8%, water 450%. Rinse with cold water for 2 minutes, then dry at 40°C for 30 minutes.
Surface Phosphating Treatment Methods
Surface Preparation Methods for Copper and Copper Alloys
[Method 1] Immerse in the following solution at 25–30°C for 1 minute:
Concentrated sulfuric acid 8%, concentrated nitric acid 25%, water 17%. Rinse with water and dry at 50–60°C.
[Method 2] Immerse in the following solution at 60–70°C for 10 minutes:
Concentrated sulfuric acid 40%, iron sulfate 4.5%, water 38%. Rinse with water and dry at 60–70°C.
[Method 3] Common solvents for degreasing include trichloroethylene, methyl ethyl ketone, and ethyl acetate.
[Method 4] Roughen the surface using sandblasting or sanding cloth, then degrease.
[Method 5] Dip for 1–2 minutes at 25–30°C in the following solution:
[Method 6] Immerse in the following solution at 25–30°C for 10–15 minutes:
Concentrated sulfuric acid 10%, sodium dichromate 5%, water 85%. Rinse with water and dry at room temperature.
Ferric chloride 15%, concentrated nitric acid 30%, water 200%. Rinse with water and dry at room temperature.
[Method 7] Oxidize in the following solution:
Potassium persulfate 1.5%, sodium hydroxide 5%, water 100%. Immerse at 60–70°C for 15–20 minutes. The surface turns black, and it should be scrubbed with carbon tetrachloride before bonding. This method is used for copper foil.
[Method 8] After degreasing, etch in the following solution for 10 minutes at 66–71°C:
Iron sulfate 4.5%, concentrated sulfuric acid 3.4%, water 450%. Rinse with cold water at 20°C for 5 minutes, then dip in the following solution:
Sodium dichromate 5%, concentrated sulfuric acid 10%, water 85%. Rinse with cold water, immerse in ammonium hydroxide (d=0.85) for 10 minutes, rinse with cold water for 5 minutes, wash with distilled water, and dry at 40°C. This method is used for brass and bronze.
[Source: Hefei Xianghe Phosphate Coatings Co., Ltd. http://, please cite the source!]