CN102660736B - Magnesium alloy surface conversion treatment liquid and treatment method thereof - Google Patents

Abstract

A magnesium alloy surface conversion treatment liquid and a treatment method thereof. Its components and contents are: phytic acid: 5-45g/l, calcium nitrate: 0.1-3g/l, sodium tartrate: 0.1-5g/l and ammonium metavanadate: 0.1-3g/l. The surface treatment methods of magnesium alloys are: mechanical pretreatment; degreasing and degreasing; pickling; conversion; drying. The magnesium alloy surface conversion treatment solution of the present invention does not contain environmental pollution components such as chromium and fluorine, and the treatment method is simple and efficient, and can improve the density of the film layer and the corrosion resistance and adhesion of the organic coating of the magnesium alloy. It can be widely used in the surface coating pretreatment of magnesium alloy castings, profiles and magnesium alloy products.

Description

A kind of magnesium alloy surface conversion treatment liquid and its treatment method

technical field

The invention relates to a surface conversion treatment liquid and a treatment method thereof, in particular to a magnesium alloy conversion treatment liquid and a conversion treatment method.

Background technique

Magnesium alloy has the characteristics of high specific strength and specific stiffness, good casting performance, excellent electrical shielding and damping performance, and recyclability. It is widely used in aerospace, automobiles and motorcycles, tools, electronic communications, optical instruments, computer manufacturing, etc. field. Since the electrode potential of the magnesium alloy is extremely negative (-2.36V), and the volume ratio of the natural oxide film to the metal itself is less than 1, it is not enough to protect the magnesium alloy matrix, and its corrosion resistance is poor. In order to improve the corrosion resistance of the magnesium alloy surface, many protective treatment methods have been developed, such as: chemical conversion, anodic oxidation, micro-arc oxidation, metal coating, vapor deposition and organic coating. Among them, the chemical conversion method has attracted much attention due to its advantages of simple process, low cost, not affected by the shape and size of the workpiece, and strong binding force with organic coatings. The chemical conversion method can be divided into chromate conversion method and chromium-free conversion method according to whether the treatment liquid contains chromium. The chromate conversion process is mature, and the performance of the conversion coating is excellent, but the treatment solution contains toxic chromium ions, which is extremely harmful to the human body and the environment. Therefore, the development of environment-friendly treatment liquid and treatment process has become an inevitable trend of chemical conversion treatment.

Due to the extremely high chemical activity of magnesium alloys, no single solution to the corrosion resistance of magnesium alloys under harsh conditions has been developed so far. After chemical conversion or anodic oxidation, magnesium alloys need further coating or sealing to greatly improve the corrosion resistance of magnesium alloys. Corrosion resistance. Therefore, the coating pretreatment film requires good corrosion resistance and bonding force with the paint film.

Patent No. 200710307863.3 Invention Patent "A Film Forming Solution of Magnesium Alloy Chemical Conversion Coating and the Preparation Method of the Conversion Coating", using ceric sulfate 10-80g/l, sulfuric acid 3-60ml/l, phytic acid 1-10ml /l, corrosion inhibitor 0.5~5g/l and buffering agent 0.5~5g/l aqueous solution to prepare conversion film, the conversion film layer has good compactness, good corrosion resistance and wear resistance, and high adhesion to the base layer . However, the solution contains rare earth elements, and the cost is relatively high.

The publication number is CN102268668A patent "Preparation Method of Magnesium Alloy Surface Conversion Coating", which uses a solution with a concentration of 1 to 25 g/l to prepare a phytic acid conversion coating of trivalent or higher metals. The reagents used in this process are all environmentally friendly, and the conversion coating Excellent adhesion to organic paint films. The solution component is only phytic acid, which affects the film-forming efficiency and stability of the conversion solution.

In addition, the phosphate conversion coating commonly used for magnesium alloys has better corrosion resistance and is a good coating primer, but the conversion coating is prone to wide cracks and coarse grains.

Contents of the invention

The purpose of the present invention is to propose a chromium-free, fluorine-free magnesium alloy conversion treatment solution, which is to add corrosion inhibitor, crystallization refiner and accelerator through phytic acid, which can improve the film density and the organic coating of magnesium alloy Corrosion resistance and adhesion.

Another object of the present invention is to propose a simple and efficient conversion treatment method for magnesium alloys.

The composition and content of the magnesium alloy conversion treatment solution of the present invention are: phytic acid: 5-45g/l, calcium nitrate: 0.1-3g/l, sodium tartrate: 0.1-5g/l and ammonium metavanadate: 0.1-3g/l l.

The preferred components and contents of the magnesium alloy conversion treatment solution of the present invention are: phytic acid: 15-25 g/l, calcium nitrate: 1-2 g/l, sodium tartrate: 2-4 g/l and ammonium metavanadate: 0.5-2 g/l 1.5g/l.

The optimum composition and content of the magnesium alloy conversion treatment liquid of the present invention are: phytic acid: 20g/l, calcium nitrate: 2g/l, sodium tartrate: 1g/l and ammonium metavanadate: 2g/l.

The magnesium alloy surface treatment method of conversion treatment liquid of the present invention is:

1. Mechanical pretreatment: polish the magnesium alloy surface with 400~1000# sandpaper;

2. Degreasing and degreasing: treat with 5-10% NaOH, 5-10% Na ₂ SiO ₃ and 5g/l triethanolamine solution at a temperature of 45-55°C for 1-2 minutes;

3. Pickling: use H ₃ PO ₄ 15-25g/l and Na ₃ PO ₄ 10-20g/l solution, and treat at room temperature for 10 seconds to 2 minutes;

4. Transformation: immerse the above-mentioned treated magnesium alloy into the transformation treatment solution whose pH value is adjusted to 1.5-5 with triethanolamine, and treat at room temperature for 5-30 minutes;

5. Drying: Dry at 105±5°C for 2-10 minutes or blow dry.

The conversion treatment liquid of the present invention does not contain environment-polluting components such as chromium and fluorine, and is environment-friendly. The phytic acid component in the conversion treatment solution is the main film-forming agent with a concentration of 5-45g/l. It chelates with the magnesium alloy interface and metal ions under acidic conditions to form insoluble phytate. The concentration of phytic acid can be adjusted within the specified range. If the concentration is too high, complexes will easily appear, and if the concentration is too low, the film formation will be incomplete. The calcium nitrate component is an accelerator with a concentration of 0.1-3g/l, which accelerates the formation of the conversion film, so that the conversion film can be formed in a short time at room temperature. The concentration of calcium nitrate can be adjusted within the specified range, but it is easy to Forms chelates with phytic acid and precipitates at higher pH. Ammonium metavanadate is a crystal refiner with a concentration of 0.1-3g/l, which can make the crystallization of the conversion film fine and uniform, and improve the density and quality of the conversion film. The concentration of ammonium metavanadate can be adjusted within the specified range, but if the concentration is too high It is easily reacted by nitrate ions to produce vanadium trioxide, and loses the effect of crystal refiner. Sodium tartrate is a corrosion inhibitor with a concentration of 0.1-5g/l. It can stabilize the pH of the solution and keep the conversion treatment solution within the effective range for a long time. The concentration of sodium tartrate can be adjusted within the specified range. If the concentration is too high, complexes will easily appear. The magnesium alloy conversion treatment solution of the present invention can make the AZ series and ZK series magnesium alloys form a film within a few minutes at room temperature, and the film layer has good density, excellent corrosion resistance, and strong adhesion to the base material and the surface coating. The conversion treatment solution of the present invention does not contain environmental pollution components such as chromium and fluorine, and the treatment method is simple and efficient, and can be widely used in the surface coating pretreatment of magnesium alloy castings, profiles and magnesium alloy products.

Description of drawings

Fig. 1 is the surface microscopic appearance of embodiment 5 conversion film;

Fig. 2 is the comparison chart of the corrosion weight loss of the conversion coating of the embodiment and the die-casting AZ91D in 5% NaCl aqueous solution;

Fig. 3 is an organic coating adhesion test chart of the conversion film in Example 5.

Detailed ways

Example 1

The composition and content of the magnesium alloy conversion treatment solution are phytic acid: 20g/l, calcium nitrate: 2g/l, sodium tartrate: 1g/l and ammonium metavanadate: 2g/l.

Example 2

The composition and content of the magnesium alloy conversion treatment solution are phytic acid: 5g/l, calcium nitrate: 1g/l, sodium tartrate: 0.5g/l and ammonium metavanadate: 0.2g/l.

Example 3

The components and contents of the magnesium alloy conversion treatment solution are phytic acid: 45g/l, calcium nitrate: 3g/l, sodium tartrate: 0.2g/l and ammonium metavanadate: 1g/l.

Example 4

The composition and content of the magnesium alloy conversion treatment solution are phytic acid: 15g/l, calcium nitrate: 0.2g/l, sodium tartrate: 4.5g/l and ammonium metavanadate: 3g/l.

Example 5

1. Mechanical pretreatment: use 400~1000# sandpaper to polish the surface of the die-casting AZ91D magnesium alloy in sequence;

2. Degreasing and degreasing: use 8% NaOH, 8% Na ₂ SiO ₃ and 5g/l triethanolamine solution at a temperature of 45°C for 2 minutes;

3. Pickling: use H ₃ PO ₄ 20g/l and Na ₃ PO ₄ 15g/l solution at room temperature for 30 seconds;

4. Transformation: adjust the pH value of the conversion treatment solution in Example 1 to 4 with triethanolamine, and place the above-mentioned treated magnesium alloy in the conversion treatment solution for 10 minutes at room temperature;

5. Blow dry.

The weight loss of the die-casting AZ91D magnesium alloy after the above treatment was 8% after immersion in 5% NaCl solution for 10 days, and the subsequent cross-cut test of the organic coating showed that its adhesion reached 0 grade.

Example 6

1. Mechanical pretreatment: use 400~1000# sandpaper to polish the surface of the die-casting AZ91D magnesium alloy in sequence;

2. Degreasing and degreasing: treat with 5% NaOH, 10% Na ₂ SiO ₃ and 5g/l triethanolamine solution at a temperature of 50°C for 1 minute;

3. Pickling: use H ₃ PO ₄ 15g/l and Na ₃ PO ₄ 10g/l solution at room temperature for 60 seconds;

4. Transformation: adjust the pH value of the conversion treatment solution in Example 2 to 2 with triethanolamine, and place the above-mentioned treated magnesium alloy in the conversion treatment solution for 5 minutes at room temperature;

5. Blow dry.

The weight loss of the die-casting AZ91D after the above treatment was 70% after immersion in 5% NaCl solution for 10 days.

Example 7

1. Mechanical pretreatment: use 400~1000# sandpaper to polish the surface of the die-casting AZ91D magnesium alloy in sequence;

2. Degreasing and degreasing: treat with 10% NaOH, 5% Na ₂ SiO ₃ and 5g/l triethanolamine solution at a temperature of 45°C for 1 minute;

3. Pickling: use H ₃ PO ₄ 20g/l and Na ₃ PO ₄ 5g/l solution at room temperature for 40 seconds;

4. Transformation: adjust the pH value of the conversion treatment solution in Example 3 to 3 with triethanolamine, and place the above-mentioned treated magnesium alloy in the conversion treatment solution for 15 minutes at room temperature;

5. Blow dry.

The weight loss of the die-casting AZ91D after the above treatment was 50% after immersion in 5% NaCl solution for 10 days.

Example 8

1. Mechanical pretreatment: use 400~1000# sandpaper to polish the surface of the die-casting AZ91D magnesium alloy in sequence;

2. Degreasing and degreasing: use 10% NaOH, 10% Na ₂ SiO ₃ and 5g/l triethanolamine solution at a temperature of 50°C for 1 minute;

3. Pickling: use H ₃ PO ₄ 20g/Na ₃ PO ₄ 15g/l solution, treat at room temperature for 20 seconds;

4. Transformation: adjust the pH value of the conversion treatment solution in Example 2 to 2.6 with triethanolamine, and place the above-mentioned treated magnesium alloy in the conversion treatment solution for 20 minutes at room temperature;

5. Blow dry.

The weight loss of the die-casting AZ91D after the above treatment was 18% after immersion in 5% NaCl solution for 10 days.

Claims (4)

1. a Mg alloy surface conversion treating solution is characterized in that component and content are: phytic acid: 5 ~ 45g/l, nitrocalcite: 0.1 ~ 3g/l, sodium tartrate: 0.1 ~ 5g/l and ammonium meta-vanadate: 0.1 ~ 3g/l.

2. conversion treating solution according to claim 1 is characterized in that component and content are: phytic acid: 15 ~ 25g/l, nitrocalcite: 1 ~ 2g/l, sodium tartrate: 2 ~ 4g/l and ammonium meta-vanadate: 0.5 ~ 1.5g/l.

3. conversion treating solution according to claim 1 is characterized in that component and content are: phytic acid: 20g/l, nitrocalcite: 2g/l, sodium tartrate: 1g/l and ammonium meta-vanadate: 2g/l.

4. surface treatment method of Mg alloy that utilizes conversion treating solution claimed in claim 1 is characterized in that:

1) mechanical pretreatment: with 400 ~ 1000# sand papering Mg alloy surface;

2) oil removing degreasing: with the NaOH of massfraction 5 ~ 10%, 5 ~ 10% Na ₂SiO ₃With the triethanolamine solution of 5g/l, temperature is 45 ~ 55 ℃ and processed 1 ~ 2 minute;

3) pickling: use H ₃PO ₄15 ~ 25g/l and Na ₃PO ₄10 ~ 20g/l solution, room temperature treatment 10 seconds ~ 2 minutes;

4) transform: the magnesium alloy of above-mentioned processing is immersed the conversion treating solution of adjusting pH value to 1.5 ~ 5 with trolamine, room temperature treatment 5 ~ 30 minutes;

5) oven dry: under 105 ± 5 ℃, dried 2 ~ 10 minutes or dry up.

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