CN102174694B - Method for preparing aluminium alloy/trivalent chromium composite conversion film and film-forming liquid thereof - Google Patents

Abstract

The invention discloses a method for preparing an aluminum alloy trivalent chromium composite conversion film and its film-forming solution. In the film-forming solution, an inorganic corrosion inhibitor divalent manganese salt and an organic corrosion inhibitor ethanolamine are added. The film-forming solution is used to Liquid treatment of aluminum or aluminum alloy workpieces can form a trivalent chromium composite conversion film on the surface of the aluminum alloy. Compared with the trivalent chromium conversion film with a single film layer, the invention improves the anticorrosion performance of the aluminum alloy and can achieve the anticorrosion effect of the hexavalent chromium chemical conversion film.

Description

Preparation method of trivalent chromium composite conversion coating on aluminum alloy and film-forming solution

technical field

The invention relates to aluminum alloy surface treatment, in particular to a method for preparing an aluminum alloy trivalent chromium composite conversion film and a film-forming solution thereof.

Background technique

In order to improve the corrosion resistance of aluminum and other metals such as zinc and steel, the traditional method is to use hexavalent chromium conversion coating. However, hexavalent chromium is toxic. In the electrical and electronic industries, the EU RoHS regulations (Restriction of Hazardous Substances, "Instructions on Restricting the Use of Certain Hazardous Substances in Electrical and Electronic Equipment") prohibit the use of hexavalent chromium compounds. In order to meet the needs of environmentally friendly processes, various hexavalent chromium-free conversion coatings have been developed. Recent research involves new conversion coatings such as titanium, tungsten, tin, zinc and rare earth salts. Because they have no color, their production operability is poor, and their practical application value is not great. The trivalent chromium conversion coating complies with RoHS regulations, has color, and has strong production operability. Therefore, there are currently many researches on the technology of trivalent chromium conversion coating on the surface of galvanized steel at home and abroad. However, different substrates have different properties, and the process of trivalent chromium conversion coating on the surface of galvanized steel cannot be used for aluminum alloy treatment. At present, there are reports on trivalent chromium-aluminum alloy conversion coatings, such as the Chinese patent "Rapid film-forming solution on aluminum alloy surface at room temperature and its application method" (application number 200710017506.3 application date March 15, 2007) of Xi'an University of Architecture and Technology, and the invention The early Chinese patent "Preparation Method of Trivalent Chromium Chemical Conversion Coating on Aluminum or Aluminum Alloy" (Application No. 200710034656.5 Application Date March 30, 2007) has a single component in the conversion coating, and its anti-corrosion performance needs to be further improved.

Contents of the invention

The technical problem to be solved by the present invention is to provide a method for preparing an aluminum alloy trivalent chromium composite conversion film and its film-forming solution, so as to improve the anticorrosion performance of the current single-component trivalent chromium conversion film.

In order to solve the above-mentioned technical problems, the present invention adopts the following technical scheme: the film-forming liquid of the aluminum alloy trivalent chromium composite conversion film, and the film-forming liquid contains:

Trivalent chromium salt 5～28g/L based on trivalent chromium ion

Phosphoric acid 5～28g/L

Divalent manganese salt 0.2～1.6g/L based on divalent manganese ion

Ethanolamines 0.1-0.6g/L in terms of ethanolamine.

The trivalent chromium salt is chromium sulfate or potassium chromium sulfate, the divalent manganese salt is manganese sulfate, and the ethanolamines are ethanolamine, diethanolamine or triethanolamine.

The pH value of the film-forming liquid is 1.5-4.0, and the temperature is 10-50°C.

A method for preparing an aluminum alloy trivalent chromium composite conversion film using the above-mentioned film-forming solution, the method comprising the following steps:

<1> Degreasing: remove the grease on the surface of the aluminum or aluminum alloy workpiece, and clean it with deionized water;

<2> Activation: Activate the aluminum or aluminum alloy workpiece treated in step <1> in an aqueous sodium hydroxide solution with a concentration of 5-60g/L and a temperature of 5-30°C for 1-2 minutes, and wash it with deionized water clean;

<3> Chromizing: Chromizing the aluminum or aluminum alloy workpiece treated in step <2> in the film-forming solution for 6-12 minutes, cleaning with deionized water, and then drying.

The drying temperature was 80°C.

In the present invention, an inorganic corrosion inhibitor divalent manganese salt and an organic corrosion inhibitor ethanolamine are added to the aluminum alloy trivalent chromium conversion coating film-forming liquid, and the film-forming liquid is used to treat aluminum or aluminum alloy two workpieces, which can be used on the aluminum alloy surface A trivalent chromium composite conversion coating is formed. Compared with the trivalent chromium conversion film with a single film layer, the invention improves the anticorrosion performance of the aluminum alloy and can achieve the anticorrosion effect of the hexavalent chromium chemical conversion film (soaking in 3.5% NaCl salt water for more than 10 days does not produce aluminum Rust), and the concentration is low, the cost is low, the conversion coating is colored, which is convenient for production control. In addition, the present invention does not use hexachromium, and the technological process and products meet the requirements of environmental protection.

Description of drawings

Fig. 1 is a process flow chart of the preparation method of the aluminum alloy trivalent chromium composite conversion film of the present invention.

Detailed ways

Fig. 1 shows the process flow of the preparation method of the aluminum alloy trivalent chromium composite conversion film of the present invention, wherein the water used in the steps of setting up the degreasing bath, activation bath, chromization bath and cleaning is deionized water.

Embodiment 12024 aluminum alloy trivalent chromium chromization

A. Build a 500L degreasing bath: Clean the container thoroughly before building the bath. For new containers or new production lines, first wash with 50L of 10% sulfuric acid solution, then wash with water twice, each time with 100L of water, and then add Henkel's degreasing agent 8KgRidoline212, and then diluted to 500L with deionized water, the pH is controlled within the range of 7-8, and mixed evenly.

B. Building an activation bath: Clean the container thoroughly before building the bath. For a new container or a new production line, first clean it with 15% sulfuric acid solution, then clean it with water, add the required 2.5Kg of sodium hydroxide, Dissolve with deionized water and dilute to 500L with deionized water, mix evenly, and keep the temperature at 30°C.

C. Build a 500L chromium bath: clean the container thoroughly before building the bath. For new containers or new production lines, first clean them with 15% sulfuric acid solution, then clean them with water, and add 10Kg Cr ₂ (SO ₄ ) ₃ and phosphoric acid 4Kg, dissolve with deionized water, add 275g of manganese sulfate and 300g of ethanolamine, add deionized water to 500L, mix well to obtain a film-forming solution, adjust the pH value to 2.3 with 15% sodium hydroxide or 10% sulfuric acid , and then heated to 10°C.

D. Preparation of trivalent chromium composite conversion coating:

<1> Degreasing: Put the aluminum or aluminum alloy workpiece in a stainless steel basket or hang it on a hanger, remove the grease on the surface of the workpiece in a degreasing bath for 8 minutes, and wash it with deionized water for 2 minutes until it is clean;

<2> Activation: activate the workpiece treated in step <1> in the activation bath for 2 minutes, and wash it with deionized water for 2 minutes until it is clean;

<3> Chromating: Chromizing the workpiece treated in step <2> in the film-forming liquid of the chromizing bath for 10 minutes, washing with deionized water for 2 minutes until clean, and then drying at 80°C for 30 minutes.

Embodiment 23003 aluminum alloy trivalent chromium chromization

A. Build a 500L degreasing bath: Clean the container thoroughly before building the bath. For new containers or new production lines, first wash with 50L of 10% sulfuric acid solution, then wash with water twice, each time with 100L of water, and then add Henkel's degreaser 9KgRidoline212, then diluted to 500L with deionized water, pH control in the range of 7-8, mix well.

B. Building an activation bath: Clean the container thoroughly before building the bath. For a new container or a new production line, first clean it with 15% sulfuric acid solution, then clean it with water, add the required 5Kg of sodium hydroxide, and then Dissolve with deionized water and then dilute to 500L with deionized water, mix well, and keep the temperature at 20°C.

C. Build a 500L chromium bath: Clean the container thoroughly before building the bath. For new containers or new production lines, first clean them with 15% sulfuric acid solution, then clean them with water, and add 16Kg Cr ₂ (SO ₄ ) ₃ and phosphoric acid 6Kg, dissolve with deionized water, add 800g of manganese sulfate and 150g of diethanolamine, add deionized water to 500L, mix well to obtain a film-forming solution, adjust the pH value to 4.0, and then heated to 20°C.

D. Preparation of trivalent chromium composite conversion coating:

<1> Degreasing: Put the aluminum or aluminum alloy workpiece in a stainless steel basket or hang it on a hanger, remove the grease on the surface of the workpiece in a degreasing bath for 8 minutes, and wash it with deionized water for 2 minutes until it is clean;

<2> Activation: activate the workpiece treated in step <1> in the activation bath for 1.5 minutes, and wash it with deionized water for 2 minutes until it is clean;

<3> Chromizing: Chromizing the workpiece treated in step <2> in the film-forming solution of the chromizing bath for 11 minutes, cleaning with deionized water for 2 minutes until clean, and drying at 80°C for 30 minutes.

Embodiment 34032 aluminum alloy trivalent chromium chromization

A. Build a 500L degreasing bath: Clean the container thoroughly before building the bath. For new containers or new production lines, first wash with 50L of 10% sulfuric acid solution, then wash with water twice, each time with 100L of water, and then add Henkel's degreaser 9KgRidoline212, then diluted to 500L with deionized water, pH control in the range of 7-8, mix well.

B. Building an activation bath: Clean the container thoroughly before building the bath. For a new container or a new production line, first clean it with 15% sulfuric acid solution, then clean it with water, add the required 25Kg of sodium hydroxide, and then Dissolve in deionized water and dilute to 500L with deionized water, mix well, and keep the temperature at 15°C.

C. Build a 500L chromium bath: clean the container thoroughly before building the bath. For new containers or new production lines, clean them with 15% sulfuric acid solution first, then clean them with water, and add 20Kg Cr ₂ (SO ₄ ) ₃ and phosphoric acid 8Kg, dissolve with deionized water, add 1000g manganese sulfate and 100g diethanolamine, then add deionized water to 500L, mix well to obtain a film-forming solution, adjust the pH value to 1.5, and then heated to 10°C.

D. Preparation of trivalent chromium composite conversion coating:

<1> Degreasing: Put the aluminum or aluminum alloy workpiece in a stainless steel basket or hang it on a hanger, remove the grease on the surface of the workpiece in a degreasing bath for 8 minutes, and wash it with deionized water for 2 minutes until it is clean;

<2> Activation: activate the workpiece treated in step <1> in the activation bath for 2 minutes, and wash it with deionized water for 2 minutes until it is clean;

<3> Chromizing: Chromizing the workpiece after step <2> in the film-forming solution of the chromizing bath for 9 minutes, washing with deionized water for 2 minutes until clean, and drying at 80°C for 30 minutes.

Embodiment 45052 aluminum alloy trivalent chromium chromization

A. Build a 500L degreasing bath: Clean the container thoroughly before building the bath. For new containers or new production lines, first wash with 50L of 10% sulfuric acid solution, then wash with water twice, each time with 100L of water, and then add Henkel's degreasing agent 8KgRidoline212, and then diluted to 500L with deionized water, the pH is controlled within the range of 7-8, and mixed evenly.

B. Building an activation bath: Clean the container thoroughly before building the bath. For a new container or a new production line, first clean it with 15% sulfuric acid solution, then clean it with water, add the required 20Kg of sodium hydroxide, and then Dissolve with deionized water and then dilute to 500L with deionized water, mix evenly, and keep the temperature at 5°C.

C. Build a 500L chromium bath: clean the container thoroughly before building the bath. For new containers or new production lines, first clean them with 15% sulfuric acid solution, then clean them with water, and add 32Kg Cr ₂ (SO ₄ ) ₃ and phosphoric acid 14Kg, dissolve with deionized water, add 1200g of manganese sulfate and 50g of triethanolamine, add deionized water to 500L, mix well to obtain a film-forming liquid, adjust the pH value to 2.0, and then heated to 50°C.

D. Preparation of trivalent chromium composite conversion coating:

<1> Degreasing: Put the aluminum or aluminum alloy workpiece in a stainless steel basket or hang it on a hanger, remove the grease on the surface of the workpiece in a degreasing bath for 8 minutes, and wash it with deionized water for 2 minutes until it is clean;

<2> Activation: activate the workpiece treated in step <1> in the activation bath for 1 minute, and wash it with deionized water for 2 minutes until it is clean;

<3> Chromating: Chromizing the workpiece treated in step <2> in the film-forming liquid of the chromizing bath for 10 minutes, washing with deionized water for 2 minutes until clean, and then drying at 80°C for 30 minutes.

Embodiment 56061 aluminum alloy trivalent chromium chromization

A. Build a 500L degreasing bath: Clean the container thoroughly before building the bath. For new containers or new production lines, first wash with 50L of 10% sulfuric acid solution, then wash with water twice, each time with 100L of water, and then add Henkel's degreasing agent 12KgRidoline212, then diluted to 500L with deionized water, the pH is controlled within the range of 7-8, and mixed evenly.

B. Building an activation bath: Clean the container thoroughly before building the bath. For a new container or a new production line, first clean it with 15% sulfuric acid solution, then clean it with water, add the required 12Kg of sodium hydroxide, and then Dissolve in deionized water and dilute to 500L with deionized water, mix well, and keep the temperature at 10°C.

C. Build a 500L chromium bath: clean the container thoroughly before building the bath. For new containers or new production lines, first clean them with 15% sulfuric acid solution, then clean them with water, and add 50Kg Cr ₂ (SO ₄ ) _3. Dissolve 12Kg of phosphoric acid in deionized water, add 1800g of manganese sulfate and 200g of diethanolamine, add deionized water to 500L, mix well to obtain a film-forming solution, and adjust the pH value to 3.8, and then heated to 35°C.

D. Preparation of trivalent chromium composite conversion coating:

<1> Degreasing: Put the aluminum or aluminum alloy workpiece in a stainless steel basket or hang it on a hanger, remove the grease on the surface of the workpiece in a degreasing bath for 8 minutes, and wash it with deionized water for 2 minutes until it is clean;

<2> Activation: activate the workpiece treated in step <1> in the activation bath for 1 minute, and wash it with deionized water for 2 minutes until it is clean;

<3> Chromizing: Chromizing the workpiece treated in step <2> in the film-forming liquid of the chromizing bath for 7 minutes, cleaning with deionized water for 2 minutes until clean, and then drying at 80°C for 30 minutes.

Embodiment 66063 aluminum alloy trivalent chromium chromization

A. Build a 500L degreasing bath: Clean the container thoroughly before building the bath. For new containers or new production lines, first wash with 50L of 10% sulfuric acid solution, then wash with water twice, each time with 100L of water, and then add Henkel's degreasing agent 12KgRidoline212, then diluted to 500L with deionized water, the pH is controlled within the range of 7-8, and mixed evenly.

B. Building an activation bath: Clean the container thoroughly before building the bath. For a new container or a new production line, first clean it with 15% sulfuric acid solution, then clean it with water, add the required 12Kg of sodium hydroxide, and then Dissolve with deionized water and then dilute to 500L with deionized water, mix well, and keep the temperature at 23°C.

C. Build a 500L chromium bath: clean the container thoroughly before building the bath. For new containers or new production lines, clean them with 15% sulfuric acid solution first, and then clean them with water. Add 12Kg Cr ₂ (SO ₄ ) _3. Dissolve 10Kg of phosphoric acid in deionized water, add 2100g of manganese sulfate and 100g of triethanolamine, add deionized water to 500L, mix well to obtain a film-forming solution, and adjust the pH value to 4.0, and then heated to 40°C.

D. Preparation of trivalent chromium composite conversion coating:

<1> Degreasing: Put the aluminum or aluminum alloy workpiece in a stainless steel basket or hang it on a hanger, remove the grease on the surface of the workpiece in a degreasing bath for 8 minutes, and wash it with deionized water for 2 minutes until it is clean;

<2> Activation: activate the workpiece treated in step <1> in the activation bath for 2 minutes, and wash it with deionized water for 2 minutes until it is clean;

<3> Chromizing: Chromizing the workpiece after step <2> in the film-forming solution of the chromizing bath for 9 minutes, washing with deionized water for 2 minutes until clean, and drying at 80°C for 30 minutes.

Embodiment 77075 aluminum alloy trivalent chromium chromization

A. Build a 500L degreasing bath: Clean the container thoroughly before building the bath. For new containers or new production lines, first wash with 50L of 10% sulfuric acid solution, then wash with water twice, each time with 100L of water, and then add Henkel's degreasing agent 12KgRidoline212, then diluted to 500L with deionized water, the pH is controlled within the range of 7-8, and mixed evenly.

B. Building an activation bath: Clean the container thoroughly before building the bath. For a new container or a new production line, first clean it with 15% sulfuric acid solution, then clean it with water, add the required 12Kg of sodium hydroxide, and then Dissolve with deionized water and then dilute to 500L with deionized water, mix well, and keep the temperature at 17°C.

C. Build a 500L chromium bath: clean the container thoroughly before building the bath. For new containers or new production lines, first clean them with 15% sulfuric acid solution, then clean them with water, and add 18Kg Cr ₂ (SO ₄ ) _3. Dissolve 12Kg of phosphoric acid in deionized water, add 2000g of manganese sulfate and 200g of triethanolamine, add deionized water to 500L, mix well to obtain a film-forming solution, and adjust the pH value to 3.0, and then heated to 40°C.

D. Preparation of trivalent chromium composite conversion coating:

<1> Degreasing: Put the aluminum or aluminum alloy workpiece in a stainless steel basket or hang it on a hanger, remove the grease on the surface of the workpiece in a degreasing bath for 8 minutes, and wash it with deionized water for 2 minutes until it is clean;

<2> Activation: activate the workpiece treated in step <1> in the activation bath for 2 minutes, and wash it with deionized water for 2 minutes until it is clean;

<3> Chromizing: Chromizing the workpiece treated in step <2> in the film-forming solution of the chromizing bath for 12 minutes, washing with deionized water for 2 minutes until clean, and drying at 80°C for 30 minutes.

Example 8 Trivalent Chromium Chromization of Aluminum Alloy Die Castings

A. Build a 300L degreasing bath: Clean the container thoroughly before building the bath. For new containers or new production lines, first wash with 50L of 20% sulfuric acid solution, then wash with water twice, each time with 60L of water, and then add Henkel's degreasing powder Ridoline 2128Kg is released to 300L, then diluted to 300L with deionized water, the pH is controlled within the range of 7-8, and mixed evenly.

B. Building an activation bath: Clean the container thoroughly before building the bath. For a new container or a new production line, first clean it with 15% sulfuric acid solution, then clean it with water, add the required 8Kg of sodium hydroxide, and then Dissolve with deionized water and then dilute to 300L with deionized water, mix well, and keep the temperature at 26°C.

C. Build a 300L chromium bath: clean the container thoroughly before building the bath. For new containers or new production lines, first clean them with 15% sulfuric acid solution, then clean them with water, and add 10Kg KCr(SO ₄ ) ₂ And phosphoric acid 6Kg, add 800g manganese sulfate and 80g triethanolamine, dissolve with deionized water, add deionized water to 300L, mix evenly to obtain a film-forming liquid, adjust the pH value to 2.5 with 15% sodium hydroxide or 10% sulfuric acid , and then heated to 50°C.

D. Preparation of trivalent chromium composite conversion coating:

<1> Degreasing: Put the aluminum or aluminum alloy workpiece in a stainless steel basket or hang it on a hanger, remove the grease on the surface of the workpiece in a degreasing bath for 8 minutes, and wash it with deionized water for 2 minutes until it is clean;

<2> Activation: activate the workpiece treated in step <1> in the activation bath for 2 minutes, and wash it with deionized water for 2 minutes until it is clean;

<3> Chromating: Chromizing the workpiece treated in step <2> in the film-forming liquid of the chromizing bath for 6 minutes, cleaning with deionized water for 2 minutes until clean, and then drying at 80°C for 30 minutes.

Comparative example 16063 aluminum alloy trivalent chromium chromization (implemented according to Chinese patent 200710034656.5)

A. Build a 400L degreasing bath: Clean the container thoroughly before building the bath. For new containers or new production lines, first wash with 40L of 20% sulfuric acid solution, then wash with water twice, each time with 80L of water, and then add Henkel's degreasing powder Ridoline2128Kg is released to 400L, then diluted to 400L with deionized water, and the pH is controlled within the range of 7-8.

B. Building an activation bath: Clean the container thoroughly before building the bath. For a new container or a new production line, first clean it with 15% sulfuric acid solution, then clean it with water, add the required 50Kg of sodium hydroxide, and then Dissolve with deionized water and then dilute to 400L with deionized water, mix well, and keep the temperature at 5-30 degrees Celsius.

C. Build a 400L chromium bath: clean the container thoroughly before building the bath. For new containers or new production lines, first clean them with 15% sulfuric acid solution, then clean them with water, and add 6Kg Cr ₂ (SO ₄ ) ₃ and phosphoric acid 5Kg, dissolve with deionized water, add deionized water to 400L, mix well, measure the pH value, if the pH value is not in the range of 1.8-4.0, adjust with 15% sodium hydroxide or 10% sulfuric acid to the range, then warm up to 50-60 degrees Celsius.

D. After the above work is ready, put the workpiece into a stainless steel basket or hang it on a hanger. After degreasing for 6 minutes, cleaning for 2 minutes, activation for 2 minutes, cleaning for 2 minutes, chromization for 6 minutes, and finally cleaning for 2 minutes , Subcutaneous drying at 100 degrees Celsius for 30 minutes to obtain a light green trivalent chromium chemical conversion coating.

Comparative example 26063 aluminum alloy hexavalent chromium chromization

A. Build a 400L degreasing bath: Clean the container thoroughly before building the bath. For new containers or new production lines, first wash with 40L of 20% sulfuric acid solution, then wash with water twice, each time with 80L of water, and then add Henkel's degreasing powder Ridoline212 8Kg is released to 400L, then diluted to 400L with deionized water, and the pH is controlled within the range of 7-8.

B. Building an activation bath: Clean the container thoroughly before building the bath. For a new container or a new production line, first clean it with 15% sulfuric acid solution, then clean it with water, add the required 20Kg of sodium hydroxide, and then Dissolve with deionized water and then dilute to 400L with deionized water, mix well, and keep the temperature at 5-30 degrees Celsius.

C. Build a 400L chromium bath: clean the container thoroughly before building the bath. For new containers or new production lines, clean them with 15% sulfuric acid solution first, and then clean them with water. Add 10Kg K ₂ Cr ₂ O ₇ and phosphoric acid 5Kg, dissolve it with deionized water, add deionized water to 400L, mix well, measure its pH value, if the pH value is not within the range of 1.8-4.0, adjust it to 15% sodium hydroxide or 10% sulfuric acid range, and then warm up to 50-60 degrees Celsius.

D. After the above work is ready, put the workpiece into a stainless steel basket or hang it on a hanger. After degreasing for 6 minutes, cleaning for 2 minutes, activation for 2 minutes, cleaning for 2 minutes, chromization for 6 minutes, and finally cleaning for 2 minutes , Dry at 100 degrees Celsius for 30 minutes to obtain a golden-yellow hexavalent chromium chemical conversion coating.

The above-mentioned aluminum alloy workpieces obtained through the treatment of Examples 1 to 8 and Comparative Examples 1 to 2 were subjected to quality inspection, and the results of technical indicators of anti-corrosion performance are shown in Table 1.

Table 1: Comparison table of anti-corrosion performance technical indicators

Conclusion: The anti-corrosion performance of the trivalent chromium conversion coating on aluminum alloy prepared by the present invention is better than the conventional trivalent chromium conversion coating on aluminum alloy in the past, and is equivalent to the hexavalent chromium conversion coating.

Claims (5)

1. the film forming liquid of the compound conversion film of aluminum alloy trivalent chromium is characterized in that this film forming liquid contains:

Chromic salt is in trivalent chromic ion 5～28g/L

Phosphoric acid 5～28g/L

Manganous salt is in divalent manganesetion 0.2～1.6g/L

Ethanolamines is in thanomin 0.1～0.6g/L.

2. the film forming liquid of the compound conversion film of aluminum alloy trivalent chromium according to claim 1 is characterized in that: said chromic salt is chromium sulphate or potassium chromium sulfate, and said manganous salt is a manganous sulfate, and said ethanolamines is thanomin, diethylolamine or trolamine.

3. the film forming liquid of the compound conversion film of aluminum alloy trivalent chromium according to claim 1 and 2, the pH value that it is characterized in that this film forming liquid is 1.5～4.0, temperature is 10～50 ℃.

4. use the preparation method of the compound conversion film of aluminum alloy trivalent chromium of the said film forming liquid of claim 3, it is characterized in that this method may further comprise the steps:

< 1>oil removing: the grease of aluminum or aluminum alloy workpiece surface is removed, and cleaned up with deionized water;

< 2>activation: the aluminum or aluminum alloy workpiece after step < 1>handled is that 5～60g/L, temperature are activation 1～2 minute in 5～30 ℃ the aqueous sodium hydroxide solution in concentration, and cleans up with deionized water;

< 3>chromaking: the chromaking 6～12 minutes in film forming liquid of the aluminum or aluminum alloy workpiece after step < 2>handled, and clean up with deionized water, be drying to obtain again.

5. use the preparation method of the compound conversion film of aluminum alloy trivalent chromium of the said film forming liquid of claim 4, it is characterized in that: said drying temperature is 80 ℃.

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