CN109023333A - Magnesium alloy moisture-proof thermal conducting-anti-corrosion chemical composition coating preparation process - Google Patents

Abstract

The invention belongs to the technical field of magnesium alloy processing, and provides a preparation process of a magnesium alloy heat and humidity resistant conductive-corrosion chemical conversion film. Corrosion-resistant chemical conversion coating; the magnesium alloy surface is given a reasonable two-phase height difference by pre-pickling treatment, and sufficient growth space is reserved for the α-phase to form Mg(OH) ₂ corrosion products; the pre-pickling treatment of magnesium alloys undergoes chemical conversion The surface of the film layer obtained by the treatment is uniform and flat, and the corrosion resistance is excellent; the film layer obtained by the chemical conversion treatment of the magnesium alloy treated before pickling has good electrical conductivity, and still has good electrical conductivity in a hot and humid environment. The preparation process has the advantages of simplicity, easy operation and low cost, and is of great significance to the engineering application of magnesium alloys in the field of 3C products.

Description

Preparation process of heat and humidity resistant conductive-corrosion chemical conversion coating on magnesium alloy

technical field

The invention belongs to the technical field of magnesium alloy processing, and relates to a chemical conversion process for obtaining corrosion resistance and ensuring electrical conductivity on the surface of magnesium alloys.

Background technique

Magnesium alloys have excellent physical and mechanical properties, and are widely used in 3C electronic products. The biggest disadvantage of magnesium alloy is that it is easy to corrode: on the one hand, it causes the failure of structure or mechanical properties; It is therefore necessary to apply protective coatings to magnesium alloys without sacrificing surface conductivity. Compared with other protective coating treatments, chemical conversion treatment has the advantages of low cost, simple operation and easy realization. Therefore, the 3C electronics industry urgently needs magnesium alloy chemical conversion coatings with high corrosion resistance and high electrical conductivity.

Damp heat test is mainly used to test whether the materials of electronic products are corroded and whether the product performance is normal in the environment of extreme high temperature and high humidity. In subtropical and tropical high-temperature and high-humidity environments, the electrical conductivity of the chemical conversion coating on the surface of magnesium alloys fails, which hinders the widespread use of AZ91D magnesium alloys in the 3C field. Moreover, the number of public reports on the conductive-corrosion-resistant film suitable for the formation of magnesium alloy chemical conversion treatment in hot and humid environment is very limited, and the coverage is very small, which cannot meet the application requirements of actual components. Therefore, there is an urgent need to develop a non-toxic, environmentally friendly treatment process for magnesium alloy conductive-corrosion chemical conversion coatings suitable for long-term hot and humid environments.

Contents of the invention

In order to overcome the above deficiencies, the technical problem to be solved by the present invention is to provide a method for preparing a conductive-corrosion-resistant chemical conversion coating suitable for magnesium alloys in hot and humid environments by combining pickling pretreatment and chemical conversion treatment.

In order to achieve the above object, the technical scheme of the present invention is as follows:

A preparation process of a magnesium alloy heat and humidity resistant conductive-corrosion chemical conversion film, comprising the following steps:

1) Grinding pretreatment: remove foreign matter on the surface of magnesium alloy and reduce surface roughness;

2) Pickling pretreatment: immerse the magnesium alloy in step 1) in a pickling solution with a temperature of 30-50°C and a concentration of 1ml/L-10ml/L for 1-20min; the pickling solution is capable of producing A pickling solution with two-phase height difference, the magnesium alloy after pickling treatment is washed with deionized water until there is no residual acid solution on the surface;

3) Chemical conversion treatment: immerse the magnesium alloy in step 2) in a chemical conversion solution with a temperature of 30-80°C and a pH value of 2-4 for 5-15 minutes to prepare a magnesium alloy with a conductive-corrosion-resistant chemical conversion film layer. alloy, and then washed with deionized water until there is no residual chemical conversion solution on the surface, and then dried.

Further, the concentration of the above pickling solution is 1ml/L˜3ml/L.

Further, the pickling solution in the above step 2) includes one or more of oxalic acid, sulfuric acid, hydrochloric acid, nitric acid or citric acid.

Further, the concentration of each component in the chemical conversion liquid in the above step 3) is: 1ml/L～5ml/L phosphoric acid, 30g/L～60g/L phosphate, 25g/L～55g/L nitrate, 1～5ml/L 4g/L vanadate, 1ml/L~6ml//L emulsifier, 10g/L~65g/L strong oxidant. This chemical conversion fluid is highly oxidizing.

Further, the above-mentioned phosphate includes: one or more of sodium phosphate, monohydrogen phosphate, dihydrogen phosphate or pyrophosphate.

Further, the above-mentioned nitrates include: one or more of sodium nitrate, potassium nitrate, calcium nitrate, and zinc nitrate.

Further, the above-mentioned vanadate includes: one or more of sodium vanadate, ammonium vanadate, and ammonium metavanadate.

Further, the above-mentioned strong oxidizing agent includes: one or more of potassium permanganate, ammonium persulfate, and molybdate.

Further, the above-mentioned emulsifier includes: one or more of OP-10, sodium dodecylbenzenesulfonate, sodium dodecylsulfate, and DDB.

Further, after the above step 1) is pre-polished, the surface of the magnesium alloy is free from foreign matter, oil, corrosion, fingerprints and burrs.

Main feature of the present invention is embodied in:

A thicker chemical conversion film is formed on the α phase, which endows the α phase with good corrosion resistance in the weak area of the magnesium alloy; at the same time, a very thin oxide film is formed on the β phase, and the β phase protrudes from the α phase Become "conductive spots", so that the chemical conversion film has good electrical conductivity.

Proper pickling pretreatment of magnesium alloy can increase the height difference between β phase and α phase, and reserve enough growth space for α phase to form Mg(OH) ₂ corrosion products. In the hot and humid test environment, it can prevent the reaction of Mg on the α phase and H ₂ O in the hot and humid environment to form Mg(OH) ₂ corrosion products higher than the second phase of β, thus improving the electrical conductivity of the chemical conversion coating in the hot and humid environment .

The beneficial effects of the present invention are reflected in:

(1) The surface of the magnesium alloy is given a reasonable height difference between the two phases through the pre-pickling treatment, and sufficient growth space is reserved for the α phase to form Mg(OH) ₂ corrosion products;

(2) The surface of the film layer obtained by the chemical conversion treatment of the magnesium alloy treated before pickling is uniform and smooth, and the corrosion resistance is superior;

(3) The film layer obtained by the chemical conversion treatment of the magnesium alloy pre-treated by pickling has good electrical conductivity, and it still has good electrical conductivity in a hot and humid environment.

(4) The preparation process has the advantages of simplicity, easy operation and low cost, which is of great significance to the engineering application of magnesium alloys in the field of 3C products.

Description of drawings

Figure 1 shows the cross-sectional morphology of the chemically converted AZ91D magnesium alloy film before and after the damp heat test, (a1) the cross-sectional morphology before the damp heat test, and (a2) the cross-sectional morphology after the damp heat test for 960 hours.

Figure 2 shows the cross-sectional morphology of the AZ91D magnesium alloy coating before and after the damp heat test after sulfuric acid pickling pretreatment and chemical conversion treatment, (b1) the cross-sectional morphology before the damp heat test, (b2) the cross-sectional morphology after the damp heat test for 960h.

Fig. 3 is a curve diagram of contact resistance change of AZ91D magnesium alloy and conductive-corrosion-resistant film without and with sulfuric acid pickling pretreatment under damp heat test.

Figure 4 is the macroscopic appearance of the salt spray test of the AZ91D magnesium alloy and the conductive-corrosion-resistant film without and with sulfuric acid pickling pretreatment. Among them, the first line is the macroscopic appearance of AZ91D magnesium alloy in salt spray test for 0h, 24h, and 48h respectively, and the second line is the macroscopic appearance of conductive-corrosion film without sulfuric acid pickling pretreatment for 0h, 24h, and 48h in salt spray test. The three behaviors are the macroscopic appearance of the conductive-corrosion film before sulfuric acid pickling for 0h, 24h, and 48h in salt spray experiments.

Detailed ways

Example 1:

The preparation method is as follows: the sample is cast AZ91D magnesium alloy;

1. Grinding pretreatment: Grinding with sandpaper to remove burrs, firm oxides, release agents, casting sand, cutting oil and other foreign matter to reduce surface roughness.

2. Pre-pickling treatment: immerse the polished sample in a sulfuric acid pickling solution with a concentration of 2ml/L at a temperature of 30°C. The etching treatment time is 5 minutes. Take out the processed sample and use a deionized Wash with water 3 times until the residual sulfuric acid solution on the surface is removed. In an acidic environment, the β second phase and the α base phase in the AZ91D magnesium alloy form a height difference of 5-10 μm due to severe galvanic corrosion, which is the Mg(OH) ₂ corrosion formed by the α base phase in the damp heat test. The product reserves a growth space, so that the height of the β second phase is higher than that of the α base phase after the damp heat test.

3. Chemical conversion treatment: the AZ91D magnesium alloy sample treated before sulfuric acid pickling is placed in a concentration of 3ml/L phosphoric acid, 35g/L disodium hydrogen phosphate, 40g/L calcium nitrate, 4g/L ammonium metavanadate, 2ml// L emulsifier, 40g/L potassium permanganate at a temperature of 45°C in the chemical conversion solution for 10 minutes. And the pH value of the chemical conversion solution is maintained at 3.3. During the chemical conversion process, the solution is stirred with a stirring bar to make the temperature distribution of the solution even and avoid the uneven surface of the film layer caused by local high temperature. After the chemical conversion treatment, wash 3 times with deionized water to remove the chemical conversion liquid remaining on the surface of the film layer, and blow dry. After chemical conversion treatment, a uniform and smooth brown-yellow film layer is formed.

4. As can be seen from the cross-sectional morphology Figures 1 and 2, compared with the AZ91D magnesium alloy and the chemical conversion coating without pickling pretreatment, after 960 hours of damp heat experiment (temperature 85 ℃, relative humidity 85%), after pickling The height of the β phase on the surface of the AZ91D magnesium alloy chemical conversion coating after pretreatment and chemical conversion treatment is still higher than that of the corrosion products on the α phase, and the β phase loses "conductive spots", and the film layer has good electrical conductivity (Figure 3).

5. It can be seen from Figure 4 that the pre-pickling treatment has no obvious impact on the corrosion resistance of the AZ91D magnesium alloy chemical conversion coating, which ensures the good corrosion resistance of the film.

Example 2:

The preparation method is as follows: the sample is cast AZ91D magnesium alloy;

1. Grinding pretreatment: Grinding with sandpaper to remove burrs, firm oxides, release agents, casting sand, cutting oil and other foreign matter to reduce surface roughness.

2. Pre-pickling treatment: immerse the polished sample in a sulfuric acid pickling solution with a concentration of 1ml/L at a temperature of 30°C. The etching treatment time is 1min. Take out the processed sample and use a deionized Wash with water 3 times until the residual sulfuric acid solution on the surface is removed. In an acidic environment, the β second phase and the α base phase in the AZ91D magnesium alloy form a height difference of 5-10 μm due to severe galvanic corrosion, which is the Mg(OH) ₂ corrosion formed by the α base phase in the damp heat test. The product reserves a growth space, so that the height of the β second phase is higher than that of the α base phase after the damp heat test.

3. Chemical conversion treatment: the AZ91D magnesium alloy sample treated before sulfuric acid pickling is placed in a concentration of 1ml/L phosphoric acid, 30g/L disodium hydrogen phosphate, 25g/L calcium nitrate, 1g/L ammonium metavanadate, 1ml// L emulsifier, 10g/L potassium permanganate and a chemical conversion solution at a temperature of 30°C for 10 minutes. And the pH value of the chemical conversion solution is maintained at 4. During the chemical conversion process, the solution is stirred with a stirring bar to make the temperature distribution of the solution even and avoid the uneven surface of the film layer caused by local high temperature. After the chemical conversion treatment, wash 3 times with deionized water to remove the chemical conversion liquid remaining on the surface of the film layer, and blow dry. After chemical conversion treatment, a uniform and smooth brown-yellow film layer is formed.

4. As can be seen from the cross-sectional morphology Figures 1 and 2, compared with the AZ91D magnesium alloy and the chemical conversion coating without pickling pretreatment, after 960 hours of damp heat experiment (temperature 85 ℃, relative humidity 85%), after pickling The height of the β phase on the surface of the AZ91D magnesium alloy chemical conversion coating after pretreatment and chemical conversion treatment is still higher than that of the corrosion products on the α phase, and the β phase loses "conductive spots", and the film layer has good electrical conductivity (Figure 3).

5. It can be seen from Figure 4 that the pre-pickling treatment has no obvious impact on the corrosion resistance of the AZ91D magnesium alloy chemical conversion coating, which ensures the good corrosion resistance of the film.

Example 3:

The preparation method is as follows: the sample is cast AZ91D magnesium alloy;

1. Grinding pretreatment: Grinding with sandpaper to remove burrs, firm oxides, release agents, casting sand, cutting oil and other foreign matter to reduce surface roughness.

2. Pickling pretreatment: immerse the polished sample in a sulfuric acid pickling solution with a concentration of 10ml/L at a temperature of 50°C. The etching treatment time is 20 minutes. Take out the processed sample and use a deionized Wash with water 3 times until the residual sulfuric acid solution on the surface is removed. In an acidic environment, the β second phase and the α base phase in the AZ91D magnesium alloy form a height difference of 5-10 μm due to severe galvanic corrosion, which is the Mg(OH) ₂ corrosion formed by the α base phase in the damp heat test. The product reserves a growth space, so that the height of the β second phase is higher than that of the α base phase after the damp heat test.

3. Chemical conversion treatment: the AZ91D magnesium alloy sample treated before sulfuric acid pickling is placed in a concentration of 5ml/L phosphoric acid, 60g/L disodium hydrogen phosphate, 55g/L calcium nitrate, 4g/L ammonium metavanadate, 6ml// L emulsifier, 65g/L potassium permanganate and a chemical conversion solution at a temperature of 80°C for 10 minutes. And the pH value of the chemical conversion solution is maintained at 2. During the chemical conversion process, the solution is stirred with a stirring bar to make the temperature distribution of the solution even and avoid the uneven surface of the film layer caused by local high temperature. After the chemical conversion treatment, wash 3 times with deionized water to remove the chemical conversion liquid remaining on the surface of the film layer, and blow dry. After chemical conversion treatment, a uniform and smooth brown-yellow film layer is formed.

4. As can be seen from the cross-sectional morphology Figures 1 and 2, compared with the AZ91D magnesium alloy and the chemical conversion coating without pickling pretreatment, after 960 hours of damp heat experiment (temperature 85 ℃, relative humidity 85%), after pickling The height of the β phase on the surface of the AZ91D magnesium alloy chemical conversion coating after pretreatment and chemical conversion treatment is still higher than that of the corrosion products on the α phase, and the β phase loses "conductive spots", and the film layer has good electrical conductivity (Figure 3).

5. It can be seen from Figure 4 that the pre-pickling treatment has no obvious impact on the corrosion resistance of the AZ91D magnesium alloy chemical conversion coating, which ensures the good corrosion resistance of the film.

It can be known from common technical knowledge that the present invention can be realized through other embodiments without departing from its spirit or essential features. Accordingly, the above-disclosed embodiments are, in all respects, illustrative and not exclusive. All changes within the scope of the present invention or within the scope equivalent to the present invention are embraced by the present invention.

Claims (10)

1. A preparation process of a magnesium alloy heat and humidity resistant conductive-corrosion chemical conversion film, is characterized in that, comprises the steps: 1) Grinding pretreatment: remove foreign matter on the surface of magnesium alloy and reduce surface roughness; 2) Pickling pretreatment: immerse the magnesium alloy in step 1) in a pickling solution with a temperature of 30-50°C and a concentration of 1ml/L-10ml/L for 1-20min; the pickling solution is capable of producing A pickling solution with two-phase height difference, the magnesium alloy after pickling treatment is washed with deionized water until there is no residual acid solution on the surface; 3) Chemical conversion treatment: immerse the magnesium alloy in step 2) in a chemical conversion solution with a temperature of 30-80°C and a pH value of 2-4 for 5-15 minutes to prepare a magnesium alloy with a conductive-corrosion-resistant chemical conversion film layer. alloy, and then washed with deionized water until there is no residual chemical conversion solution on the surface, and then dried. 2. The preparation process of the magnesium alloy heat and humidity resistant conductive-corrosion chemical conversion coating according to claim 1, characterized in that the concentration of the pickling solution is 1ml/L-3ml/L. 3. according to the preparation technology of claim 1 and 2 described magnesium alloy heat and humidity resistant conduction-corrosion resistant chemical conversion film, it is characterized in that, the pickling solution in described step 2) comprises oxalic acid, sulfuric acid, hydrochloric acid, nitric acid or lemon One or more of the acids. 4. The preparation process of the magnesium alloy heat and humidity resistant conductive-corrosion chemical conversion film according to claim 1 or 2, characterized in that the concentration of each component in the chemical conversion liquid in the step 3) is: 1ml/L ～5ml/L phosphoric acid, 30g/L～60g/L phosphate, 25g/L～55g/L nitrate, 1～4g/L vanadate, 1ml/L～6ml//L emulsifier, 10g/L～ 65g/L strong oxidizing agent. 5. The preparation process of the magnesium alloy heat and humidity resistant conductive-corrosion chemical conversion film according to claim 4, characterized in that, the phosphate comprises: sodium phosphate, monohydrogen phosphate, dihydrogen phosphate or pyrophosphoric acid One or two or more types of salt. 6. The preparation process of the magnesium alloy heat and humidity resistant conductive-corrosion resistant chemical conversion coating according to claim 4, wherein said nitrate comprises: one of sodium nitrate, potassium nitrate, calcium nitrate, and zinc nitrate Or two or more. 7. the preparation technology of magnesium alloy heat and humidity resistant conduction-corrosion resistant chemical conversion film according to claim 4 is characterized in that, described vanadate comprises: sodium vanadate, ammonium vanadate, ammonium metavanadate One or two or more. 8. The preparation process of the magnesium alloy heat and humidity resistant conductive-corrosion chemical conversion coating according to claim 4, wherein the strong oxidizing agent comprises: one of potassium permanganate, ammonium persulfate, and molybdate Or two or more. 9. The preparation process of the magnesium alloy heat and humidity resistant conductive-corrosion chemical conversion film according to claim 4, characterized in that, the emulsifier comprises: OP-10, sodium dodecylbenzenesulfonate, dodecylbenzenesulfonate, One or more of sodium alkyl sulfate and DDB. 10. The preparation process of the magnesium alloy heat and humidity resistant conductive-corrosion chemical conversion film according to claim 1, characterized in that, after the step 1) is polished and pretreated, the surface of the magnesium alloy is free from foreign matter, oil, and corrosion. , Fingerprints And Glitches.