BE1028187B1 - Process for the production of chromium- and phosphorus-free chemical film on aluminum alloy surface - Google Patents

Abstract

The invention discloses a method for producing chromium and phosphorus free chemical film on aluminum alloy surface, the conversion solution formula used comprising: 0.8-3.2 mL / L H2TiF6, 0.2-1.6mL / L H2ZrF6, 0.25- 0.5g / L salicylic acid and 0.1-0.2g / L Ce (N03) 3 · 6H2O. The film forming process of the present invention is free of chromium and phosphorus and is environmentally friendly, and the chemical film obtained by the method of the present invention has better corrosion resistance and a better combination with a paint film.

Description

; BE2021 / 5018 Process for the production of chromium- and phosphorus-free chemical film on aluminum alloy surface

TECHNICAL FIELD The invention relates to the field of surface treatment of aluminum alloys. In particular, the present invention relates to a method for producing a chromium-free and phosphorus-free chemical film on an aluminum alloy surface. The invention discloses a method of making chromium and phosphorus free chemical film.

BACKGROUND ART Aluminum and its alloys have high specific strength, excellent ductility, high thermal conductivity and are widely used in the aerospace, construction and transportation industries. Various series of aluminum alloys play an important role in the advanced manufacturing process, but under natural conditions the surface of the pure aluminum alloy has a thin oxide layer and is brittle and has a low bond strength with the coating. Aluminum alloys tend to corrode, especially under humid conditions. Therefore, before painting, the aluminum alloy must be subjected to an effective treatment to improve its strength. In order to improve the surface properties of aluminum alloys, researchers have studied various surface modification technologies and obtained thin coating by various surface treatment methods such as metal matrix composites, plasma spraying, thermal spraying, electroplating and hard anodizing, with the thin coating having better property. However, due to the poor adhesion of the coating to the substrate, these technologies are used less frequently. The titanium-zirconium conversion film is excellent in bonding force with the coating lacquer film, and the titanium / zirconium metal salt is slightly toxic or non-toxic and is relatively inexpensive. It can be used as the main salt to replace hexavalent chromium. The disadvantage of the titanium-zirconium conversion film is that it has poor corrosion resistance and many manufacturing processes are not environmentally friendly. There is therefore an urgent need to develop a method for producing an environmentally friendly and corrosion-resistant, chromium-free and phosphorus-free chemical film on an aluminum alloy surface.

SUMMARY OF THE PRESENT INVENTION In order to achieve the above objects, the present invention provides a method for producing a chromium-free and phosphorus-free chemical film on aluminum alloy surface, the conversion solution formula used

° BE2021 / 5018 includes: 0.8-3.2 mL / L HsTiFs, 0.2-1.6mL / L H2ZrFe, 0.25-0.5g / L salicylic acid and 0.1-0.2g / L Ce (N03) 3: 6H20.

Preferably, in the method for producing the chromium-free and phosphorus-free chemical film on the aluminum alloy surface, the specific operation is: placing an aluminum alloy to be treated in a conversion solution mentioned above and performing conversion treatment.

Preferably, in the method for producing the chromium-free and phosphorus-free chemical film on the aluminum alloy surface, the concentration of the above salicylic acid is 0.35 g / L.

Preferably, in the method for producing the chromium-free and phosphorus-free chemical film on the aluminum alloy surface, the pH of the above conversion liquid is 3.5 to 4.5.

Preferably, in the method of forming the chromium-free and phosphorus-free chemical film on the aluminum alloy surface, the conversion treatment is carried out at 25-35 ° C.

In the method for producing the chromium- and phosphorus-free chemical film on the aluminum alloy surface, the concentration of the H2TiFs is preferably 4mL / L.

In the process for producing the chromium-free and phosphorus-free chemical film on the aluminum alloy surface, the concentration of the H2ZrFs is preferably 0.4mL / L.

Preferably, in the method for producing the chromium-free and phosphorus-free chemical film on the aluminum alloy surface, the concentration of the above Ce (NO 3) 3-6H 2 O is 0.14 g / l.

The present invention comprises at least the following advantageous effects: The film forming method of the present invention is free of chromium and phosphorus and is environmentally friendly, and the chemical film obtained by the method of the present invention has better corrosion resistance and a better combination with a paint film. This is because salicylic acid, as a derivative of phenol, can chemically adsorb or polymerize at the substrate interface under certain conditions.

In addition, during the film formation process, the nucleic acid bond in the salicylic acid and the hydroxyl group are ester-bonded and can be combined with the titanium ion, which has a good coordination effect and greatly facilitates the stable formation of the chemical conversion film, thereby greatly improving the corrosion resistance.

Other advantages, objects, and features of the present invention will be embodied in part by the following description, and in part understood by those skilled in the art through research and practice of the present invention.

° BE2021 / 5018

BRIEF DESCRIPTION OF THE DRAWING Figure 1 shows the surface morphology of titanium-zirconium conversion films obtained under different reaction times; FIG. 2 shows the cross-sectional morphology of the titanium-zirconium conversion films obtained in Example 8.

DETAILED DESCRIPTION The present invention will now be described in more detail with reference to the embodiments so that those skilled in the art can, according to the text of the description, implement the invention.

1. Experimental part

1.1 Film forming process The base material is AA6061 aluminum alloy. First, the substrate ZHM-1026 (purchased from the conversion film department of the Wuhan Institute of Material Protection) is subjected to a one-step acid degreasing treatment and then immersed in the conversion solution to form a film. The conversion solution formula and the process conditions are: H: TiF5 0.8 = 32 mLL, H2ZrFs 02 - 1.6 mLL, sodium hexametaphosphate 0.1-0.5 g / L, Ce (N03) 3: 6H20 0.1 - 0, 2 g / L, pH value 3.5 to 4.5, reaction temperature 25 to 35 ° C, reaction time 90 to 150s. The chemical reagents used are all chemically pure. The film-forming samples were naturally air dried and subjected to a performance test after aging for 24 hours.

1.2 Performance test

1.2.1 Copper Sulphate Drop Test The copper sulfate drop test was used to assess the corrosion resistance of the titanium-zirconium conversion film and the time it took for the drop to change from sky blue to light red. The composition of the drops is: 13 mL / L hydrochloric acid, 41 g / L copper sulfate pentahydrate and 35 g / L sodium chloride.

1.2.2 Electrochemical test The electrochemical workstation CHI660D was used for electrochemical tests. 3.5% sodium chloride solution is used as the test medium. Start the Tafel curve test when the open circuit potential in the sodium chloride solution is stable. The sampling rate is 0.01 V / s and the sampling range is -1.1 - -0.5V.

1.2.3 SEM and EDS analysis A Sigma 300 scanning electron microscope was used to observe the surface morphology and the cross-sectional morphology of the titanium-zirconium conversion film, the accelerating voltage being 20 kV. An energy spectrometer was used to analyze the chemical composition of the titanium-zirconium conversion film.

2nd Embodiment All of the following embodiments adopt the above-mentioned conversion treatment method: Example 1 When H2ZrFe is 0.2 mL / L, salicylic acid is 0.3 g / L, Ce (N03) 3: 6H2O is 0.14 g / L, pH- Value is 4.5, the reaction temperature is 30 ° C and the reaction time is 90s, the influence of the different volume fraction of H2TiFs on the corrosion resistance of the titanium-zirconium conversion film was investigated. Table 1: Influence of the volume fraction of H2TiFs on the corrosion resistance of the titanium-zirconium conversion film HeTiFe / (mL: L1) dropping time / s Jorr! (HA cr?) 0 32 5.216 1 103 1.256 2 129 0.832 4 132 0.687 8 111 1.228 Example 2 When H2TiFs is 4 mL / L, salicylic acid is 0.3 g / L, Ce (N03) 3: 6H2O0 0.14 g / L, pH 4.5, reaction temperature 30 ° C and reaction time 90s, the influence of the different volume fraction of H2ZrFs on the corrosion resistance of the titanium-zirconium conversion film was investigated.

Table 2: Influence of the volume fraction of H2ZrFs on the corrosion resistance of the titanium-zirconium conversion film H2ZrFe / (ML: L ") drop time / s Jorr! (HA cr?) 0 61 2.538 0.2 121 0.909 0.4 131 0.533 0, 8 128 0.777 1.5 108 0.948 5 Example 3 If H: TiFe is 4 mL / L, H2ZrFs is 0.4 mL / L, salicylic acid is 0.3 g / L, pH is 4.5, reaction temperature is 30 ° C and the reaction time is 90 seconds, the influence of the mass concentration of Ce (N0: 3) 36H2O0 on the corrosion resistance of the titanium-zirconium conversion films was examined, the results being shown in Table 3.

Table 3: Influence of the mass concentration of Ce (N0:) 3: 6H2O0 on the corrosion resistance of the titanium-zirconium conversion film Ce (N03) 3: 6H20 / (g-L!) Dropping time / s Jorr! (HA cr?) 0 82 1.104 0.07 123 0.711 0.14 159 0.458 0.2 131 0.681 0.3 101 0.834 Example 4 If H2TiFs is 4 mL / L, H2ZrFs is 0.4 mL / L, Ce (NO3) 3 : 6H2O is 0.14 g / L, pH is 4.5, reaction temperature is 30 ° C and reaction time is 90s, the influence of the mass concentration of salicylic acid on the corrosion resistance of the titanium-zirconium conversion film was investigated:

Table 4: Influence of the mass concentration of salicylic acid on the corrosion resistance of the titanium-zirconium conversion film Salicylic acid / (g: L ”) dropping time / s Jorr! (aA er?) 0 126 0.834 0.25 136 0.637 0.30 158 0.501 0.35 178 0.337 0.50 169 0.414 Example 5 If H2TiFs is 4 mL / L, H2ZrFe is 0.4 mL / L, salicylic acid 0.35 g / L, Ce (N03) 3: 6H2O is 0.14 g / L, pH is 4.5 and the reaction temperature is 30 ° C, the influence of the reaction time on the corrosion resistance of the titanium-zirconium conversion film was examined, wherein the results are shown in Table 5.

Table 5: Influence of the reaction time on the corrosion resistance of the titanium-zirconium conversion film reaction time / s drip time / s Jorr! (4A err?) 60 82 1.252 90 113 0.941 120 183 0.348 150 166 0.479 300 159 0.502 Figure 1 shows the surface morphology of the titanium-zirconium conversion film that was obtained under different reaction times, (a) Os, (b) 60s, ( c) 1205, (d) 180s.

From Figure 1 it can be seen that the surface of the exposed AA6061 aluminum alloy is relatively smooth, there are only a few scratches and grooves during processing.

When the reaction time is 60 seconds, the evolution of hydrogen causes a large number of pores with a pore size of 1 to 10 µm to form a porous structural film on the surface of the substrate.

When the response time is 120 seconds, the cracks on the surface of the titanium-zirconium conversion film have substantially disappeared.

If the response time is 180s,

Cracks start to appear on the titanium-zirconium conversion film due to the stacking of film-forming particles.

Example 6 If H2TiFs is 4 MUL, H2ZrFs is 0.4 mL / L, salicylic acid is 0.35g / L, Ce (N03) 3: 6H2O is 0.14 g / L, pH is 4.5 and reaction time is 120s, The influence of the reaction temperature on the corrosion resistance of the titanium-zirconium conversion films was examined, and the results are shown in Table 6.

Table 6: Influence of the reaction temperature on the corrosion resistance of the titanium-zirconium conversion film Reaction temperature / ° C dropping time / s Jorr! (HA cr?) 99 1.083 138 0.684 175 0.455 184 0.339 162 0.410 Example 7 When H2TiFs is 4 MUL, H2ZrFs is 0.4 mL / L, salicylic acid is 0.35 g / L, 15 Ce (NOs) ;: 6H2O 0.14 g / L, the reaction temperature is 30 ° C, and the reaction time is 120 seconds, the influence of pH on the corrosion resistance of the titanium-zirconium conversion films was examined, and the results are shown in Table 7.

Table 7: Influence of the pH value on the corrosion resistance 20 of the titanium-zirconium conversion film pH value dropping time / s Jorr! (HA: Grm?) 3.0 113 0.988 3.5 138 0.602 4.0 189 0.207 4.5 175 0.454 5.0 162 0.512

Example 8 (the best example) Here, H2TiF6 is 4 mL / L, H2ZrF6 is 0.4 mL / L, Ce (N03) 3-6H20 is 0.14 g / L, salicylic acid is 0.35g / L, reaction time is 1205, reaction temperature is 30 ° C and pH is 4.0.

FIG. 2 shows the cross-sectional morphology of the titanium-zirconium conversion films obtained in Example 8. It can be seen from Figure 2 that the titanium-zirconium conversion film and the aluminum alloy AA6081 are well combined and there is no obvious interface. At this time, the thickness of the titanium-zirconium conversion film is 1.2 µm.

Table 8 shows the chemical composition of the titanium-zirconium conversion films obtained in Example 8. It can be seen from Table 8 that the main elements of the titanium-zirconium conversion films are Al, O, Ti, C and Mg, and the total mass fraction of the three elements Al, O and C is about 95%. It is further confirmed that the conversion film produced by the invention is free of phosphorus and chromium, environmentally friendly and harmless.

Table 8: Chemical Composition of Titanium-Zirconium Conversion Film Element Mass Fraction (%) Atomic Fraction (%) Al 78.56 71.43 O 8.43 12.93 Ti 5.13 2.63 C 5.08 10.34 Mg 1 , 37 1.26 F 0.56 0.72 si 0.63 0.55 Fe 0.20 0.09 Zr 0.04 0.01 Measurement of the film binding force Paint performance of the conversion film Using a 100-grid knife according to the one in the national standard GB / T9286-1998 "Paints and varnishes - cross-sectional test" described test method to scratch the surface of the test piece once horizontally and vertically, and to obtain 100 square grids with 1mm ° that the matrix is exposed at the scratches, the Substrate must be exposed at the scratches. Sticking the special 3M adhesive tape on the entire cross-sectional area after cross cutting and then quickly tearing off the adhesive tape.

° BE2021 / 5018 Repeat this process five times. Use a magnifying glass to see if the paint film is peeling off in the cross-sectional area. Here, the painting performance of the conversion film is evaluated according to the peeling state of the paint.

The cross-sectional method is used to study the adhesion of paint film, gray paint and conversion film. According to the evaluation standard of GB9286-98, the combination of conversion film and primer of the present invention achieved standard gB9286-98. Class O (Table 3.21), whereby the combination of paint film, gray paint and conversion film is extremely good and meets the relevant standards of industrial production.

Table 9 Result of cross-sectional test LE EmptyProbe 1 Ti-Zr conversion film - paint 3 Level2 1 level gray paint Level 2 Level 0 From Table 9, it can be seen that the bonding force of the conversion film of the present invention and the paint film is very good and meets the industry standard. This is because salicylic acid can be combined with Ti ** by chemical absorption of the ester bond and has a good chelating effect.

Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the description and the embodiments. They can be applied to various fields suitable for the present invention. It may be easy for those familiar with the field Without departing from the general concept defined by the claims and the equivalent scope, therefore, the present invention is not limited to the specific details and the embodiments shown and described herein.

Claims (8)

EXPECTATIONS 1. A process for the production of chromium- and phosphorus-free chemical film on aluminum alloy surface, characterized in that the conversion solution formula used comprises: 0.8-3.2 mL / L H2TiFe, 0.2-1.6mL / L H2ZrFe, 0, 25-0.5g / L salicylic acid and 0.1-0.2g / L Ce (NO0:) 3: 6H20. 2. A method for producing chromium-free and phosphorus-free chemical film on aluminum alloy surface according to claim 1, characterized in that the specific working step is: placing an aluminum alloy to be treated in a conversion solution mentioned above and performing conversion treatment. 3. A method for producing chromium-free and phosphorus-free chemical film on aluminum alloy surface according to claim, characterized in that the concentration of the above salicylic acid is 0.35 g / l. 4. The method for producing chromium-free and phosphorus-free chemical film on aluminum alloy surface according to claim 1, characterized in that the pH of the above conversion liquid is 3.5 to 4.5. 5. A method for producing a chromium-free and phosphorus-free chemical film on an aluminum alloy surface according to claim 1, characterized in that the conversion treatment is carried out at 25-35 ° C. 6. Process for the production of chromium- and phosphorus-free chemical film on aluminum alloy surface according to claim 1, characterized in that the concentration of the H2TiFs is 4mL / L. 7. Process for the production of chromium- and phosphorus-free chemical film on aluminum alloy surface according to claim 1, characterized in that the concentration of the H2ZrFs is 0.4mL / L. 8. Process for the production of chromium- and phosphorus-free chemical film on aluminum alloy surface according to claim 1, characterized in that the concentration of Ce (NO3) 3: 6H2O is 0.14g / L.