WO2011080165A1

WO2011080165A1 - Surface treatment composition and solution for light metals or alloys thereof and surface treatment method

Info

Publication number: WO2011080165A1
Application number: PCT/EP2010/070435
Authority: WO
Inventors: Xiaoshan Wan; Xiangrong Wang
Original assignee: Henkel Ag & Co. Kgaa
Priority date: 2009-12-31
Filing date: 2010-12-21
Publication date: 2011-07-07
Also published as: CN102115880B; CN102115880A

Abstract

The present invention discloses surface treatment composition for light metals or alloys thereof, which comprises titanium-containing compound, a vanadium-containing compound, and an organic acid. The present invention also provides a surface treatment solution for light metals or alloys thereof, which comprises titanium element in water-soluble form, vanadium element in water-soluble form, an organic acid and water, wherein said organic acid contains 1-100 carbon atoms, 2-50 oxygen atoms. The present invention also provides a surface treatment method for light metals or alloys thereof, which comprises pre-treating light metals or alloys thereof, then contacting with the surface treatment solution of the present invention. The surface treatment solution of the present invention is suitable for a plurality of light metals or alloys thereof to improve their corrosion resistance, coating performance and surface conductivity, is chromium-free formulation, and is easy to formulate and is stable. The surface treatment solution satisfies environment protection requirements, and is characterized by a wide operation application range, easiness in removing its residue, and good industry applicability.

Description

Henkel AG & Co. KGaA

Surface Treatment Composition And Solution For Light Metals Or Alloys Thereof And Surface

Treatment Method

Technical Field:

The present invention relates to a surface treatment composition for light metals or alloys thereof, and a surface treatment solution for light metals or alloys thereof, also relates to a surface treatment method for light metals or alloys thereof.

Background Art:

A chromate containing six-valence Cr (Cr⁶⁺) is employed generally in the surface treatment method of aluminum, aluminum alloys, magnesium, and magnesium alloys, so as to form a layer of protection coating on the surfaces. The chromate treatment can be classified into two types, one containing six-valence Cr in the protection coating, another containing no six-valence Cr in the protection coating. But there are six-valence Cr in the waste solution for both the type, which does not satisfy environment protection requirements. Therefore it is necessary to develop a surface treatment method containing no Cr to replace the treatment formulation containing Cr. Currently available surface treatment solutions containing no Cr comprise potassium permanganate systems (CN 1386902, CN1632169, CN1786270), halide systems (CN101096758, CN1294204, CN 1475602, CN1730726, CN1623010, CN1880503, CN1962943), molybdate systems (CN1388270), phosphate systems (CN1523133, CN 1288073, CN1219982, CN1861843, CN101089227), tartrate systems (CN101104930), rare earth salt systems (CN1786270).

Above systems are mainly aimed to surface treatment for magnesium metal and have no explicit adaptability to other light metals, moreover, their formulations are very complex.

Patent CN 1966766 disclosed a treatment method directed to magnesium alloy surface, which comprises contacting a magnesium alloy with a degreasing solution, an acidic solution, a basic solution, a chemical conversion treatment solution in this order. Wherein, the used chemical conversion treatment solution contains aqueous solution of dihydrogen phosphate, phosphoric acid and metavandate. The chemical conversion treatment solution can form a conversion coating on the surface of magnesium alloy. However, the chemical conversion treatment solution is only suitable for magnesium alloy and can not form a conversion coating on other alloy surfaces. Moreover, during a chemical conversion treatment, the chemical conversion treatment solution has to be adjusted to keep its' pH value in acidity range, i.e., pH 1 -6, which limits the operation range of the treatment solution.

Above patent also tested the magnesium alloy treated with the treatment solution for corrosion resistance. The test method includes spraying 5% NaCI solution on the treated magnesium alloy surface, 8 hours after which, the corrosion ratio of magnesium alloy is observed and expressed by the following equation:

Corrosion ratio = (the corroded region area)/(surface area of magnesium alloy)) ^χ 100%

Most of the test samples have a corrosion ratio more than 1 %, even up to 3% for some test samples 8 hours after the coating layers obtained in this patent were sprayed, however, the corrosion ratio required by customers is typically below 1 %, thus it does not satisfy customers demands.

However, in practice, the alloy surface is not only required to resist corrosion and have a good coating performance, but also required to keep good surface conductive performance of the treated metal; moreover, the stability of the treatment solution and residue removability are also necessary to be considered.

Contents of Invention:

The technical problem to be solved by the present invention is to overcome the shortcomings that prior magnesium alloy treatment solution containing no Cr is only suitable for magnesium alloy and the ability of resistance to corrosion is not very good. Thus the present invention provides a surface treatment composition and a surface treatment solution for light metals or alloys thereof, as well as a surface treatment method for light metals or alloys thereof. The surface treatment composition and the solution of the present invention contain no six-valence Cr, are suitable for a plurality of light metals and alloys thereof, improve the corrosion resistance of the treated light metals and alloys thereof, and have a good coating performance. The light metals and alloys thereof treated with the surface treatment solution of the present invention have a good surface conductivity, the treatment solution has a good stability and the residue of which has a good removability. In addition, the surface treatment method is simple to apply and suitable for industrial production.

The present invention provides a surface treatment composition for light metals or alloys thereof, which comprises the following components: a titanium-containing compound, a vanadium-containing compound and an organic acid, wherein, said organic acid contains 1-100 carbon atoms, 2-50 oxygen atoms. The surface treatment composition for light metals or alloys thereof of the present invention can be a mixture of various components or composition of which various components are separately packaged (suit package form). The composition of the present invention preferably contains less than 1 ppm of chromium, more preferably no source of chromium.

Wherein, said titanium-containing compound is a compound able to dissolve in water to form titanium ions or titanate ions. Preferably, the titanium-containing compound is one or more of titanium oxide, titanic acid, titanate, and alkoxy compound of titanium.

Said vanadium-containing compound is a compound able to dissolve in water to form vanadium ions, vanadate ions, or metavanadate ions. Preferably, the vanadium-containing compound is one or more of vanadium oxide, vanadic acid, vanadate, metavanadic acid, and metavanadate. In said surface treatment composition, the mass ratio of vanadium element of the vanadium-containing compound to titanium element of the titanium-containing compound preferably is 1 : 100 to 100: 1 , more preferably 1 :10-10:1.

Said organic acids are those that can reduce and coordinate with the titanium-containing compound and the vanadium-containing compound, which can coordinate with simple positive ion to form a coordinated compound containing complex ion, wherein the ligand binds with the center ion through a coordination bond. In the present invention, the organic acid is one or more chosen from those having 1-100 carbon atoms, preferably having 1 -10 carbon atoms, most preferably 2-8 carbon atoms and having 2-50 oxygen atoms, preferably having 2-10 oxygen atoms. Preferably, the organic acid is one or more of formic acid, acetic acid, citric acid, tannic acid and lactic acid. The mass ratio of the oxygen element of said organic acid to the vanadium element of the vanadium-containing compound preferably is 1 :20-16:1 , more preferably is 1 :10-10:1.

In one preferable embodiment of the present invention, the surface treatment composition for light metals or alloys thereof may also comprise a phosphorus-containing compound. Said phosphorus-containing compound refers to those that dissolve in water to form phosphate ion, metaphosphate ion, phosphite ion, or phosphinate ion. Said phosphorous-containing compound preferably is one or more of phosphoric acid and salts thereof, metaphosphoric acid and salts thereof, phosphorous acid and salts thereof, phosphinic acid and salts thereof and polyphosphoric acid and salts thereof. The mass ratio of the vanadium element of said vanadium-containing compound to the phosphorus element of the phosphorus-containing compound preferably is 1 :100-100:1 , and more preferably is 1 :10-10:1 . The surface composition of the present invention preferably contains less than 1 ppm, most preferably no source of fluorine.

The surface treatment composition of the present invention needs to be diluted with water prior to use, so as to form a surface treatment solution. Therefore, the present invention provides a surface treatment solution for light metals or alloys thereof, which comprises titanium element in water-soluble form, vanadium element in water-soluble form, an organic acid and water, wherein, said organic acid has 1-100 carbon atoms, preferable 1 -10 carbon atoms, and 2-50 oxygen atoms, preferable 2-10 oxygen atoms.

Wherein, the titanium element and vanadium element can deposit on the surface of the light metals or alloys thereof simultaneously during the metal conversion treatment, so as to form Ti-V system conversion coating to resist corrosion and improve the coating coating performance etc. Wherein, said water soluble form refers to one or more of ions, acid ions, meta-acid ions, hypo-acid ions, sub-acid ions etc.

Wherein, said titanium element in water-soluble form preferably is present in titanium ion and/or titanate ion in solution. The content of said titanium element in water-soluble form is preferably 0.0001 -5 %, more preferably 0.001 -0.1 % of the surface treatment solution by mass. Wherein, said vanadium element in water-soluble form preferably is present in vanadium ion, vanadate ion and metavanadate ion in the solution. The content of said vanadium element in water-soluble form is preferably 0.001-10 %, more preferably 0.01 -0.1 % of the surface treatment solution by mass.

Wherein, the mass ratio of the vanadium element in water-soluble form to the titanium element in water-soluble form preferably is 1 :100-100:1 , and more preferably 1 :10-10:1.

Wherein, said organic acids are those can reduce and coordinate with the titanium and vanadium element in water-soluble form, which can coordinate with simple positive ion to form a coordinated compound containing complex ion, wherein, the ligand binds with the center ion through a coordination bond. In the present invention, the organic acid preferably is one or more of formic acid, acetic acid, citric acid, tannic acid and lactic acid. The content of the organic acid in the surface treatment solution preferably is 0.001-1 %, more preferably is 0.01-0.1 % by mass. In another preferred embodiment of the present invention, the surface treatment solution for light metals or alloys thereof of the present invention also contains phosphorus element in water-soluble form. Wherein, during the metal conversion treatment, Ti, P, and V elements deposit on the surface of the light metals or alloys to form a Ti-P-V system conversion coating with an excellent synergistic effect among them.

Wherein, said phosphorus element in water-soluble form preferably is present in one or more of phosphate ion, metaphosphate ion, phosphite ion, or phosphinate ion in solution. The content of phosphorus element in water-soluble form preferably is 0.0001 -1 %, more preferably is 0.001-0.1 % of the surface treatment solution by mass. The mass ratio of the vanadium element in water-soluble form to phosphorus element in water-soluble form preferably is 1 :100-100:1 , and more preferably is 1 :10-10:1.

The surface treatment solution of the present invention may also comprises a pH adjuster for adjusting the pH value of the surface treatment solution to prevent it from precipitating. When the surface treatment solution has a pH of 4-11 and does not precipitate, no pH adjuster may be added. Said pH adjuster is pH adjusters commonly used in the art, preferably is an inorganic acid, an organic acid, or an inorganic base, for example, nitric acid, citric acid, or sodium hydroxide. The pH value of the surface treatment solution of the present invention preferably is 4-11 .

The content of said water is to make up the surface treatment solution to 100% by mass.

The preparation method of the surface treatment solution of the present invention is evenly blending the surface treatment composition of the present invention with water to obtain the solution, preferably by the following steps: (1 ) dissolving a vanadium-containing compound with a 10-50% by mass basic solution and filtering off impurities; (2) adding a titanium-containing compound, an organic acid and water, stirring to react completely until the solution become blue. If pH of the blue solution in step (2) is not 4-11 , the pH adjuster is used to adjust pH of the solution to range of 4-11.

Preferably, in step (2), phosphorus-containing compound may also be added. The said basic solution preferably is sodium hydroxide solution. The surface treatment solution preferably contains less than 1 ppm of chromium and/or fluorine, more preferably no source of chromium and/or fluorine.

The present invention also provides a surface treatment method for light metals or alloys thereof, which comprises the following steps: after being pre-treated, contacting the pre-treated light metals or alloys thereof with the surface treatment solution to form a coating.

Wherein, said contacting treatment may employ a conventional contacting treatment method for surface treatment in the art, such as dipping, coating, spray coating, rinsing, etc., to make the light metals or alloys thereof contact with said surface treatment solution sufficiently. Preferably, the treatment time of said contacting treatment is 2-60 minutes and the treatment temperature of said contacting treatment is 25-60°C.

Wherein, said pre-treatment is aimed to make the surface of light metals or alloys thereof as clean as possible, so as to facilitate the coating more strongly adhere to the substrate. Said pre-treatment may employ a conventional pre-treatment method or the method provided in the present invention. Preferably, the pre-treatment method provided in the present invention is employed and comprises: step (1 ) mechanically grinding; (2) degreasing; (3) acidic washing; (4) ultrasonic water washing; and (5) neutralizing with a basic solution.

In step (1 ), said mechanically grinding is aimed to remove contaminants on the surface of the light metals or alloys thereof. The mechanically grinding may refers to conventional mechanical grinding methods of the art.

In step (2), said degreasing is aimed to remove the grease on the surface of the light metals or alloys thereof. The degreasing method may be performed by using a conventional degreasing method of the art. Preferably, a basic solution is used to wash, wherein, said basic solution is NaOH solution, pH of said basic solution is preferable 10-11 , washing time of basic solution washing is preferably 3-10 minutes, and washing temperature of basic solution washing is preferably 40-80°C.

In step (3), said acidic washing refers to washing using acidic solution, acidic washing is to remove the oxide on surface of the light metals or alloys. The acidic washing method may be performed by using a conventional acidic washing method of the art. Preferably, acidic washing is performed by using water solution of organic acid, more preferably, water solution of acetic acid. pH value of said acidic solution is preferable 3-6, washing time of acidic washing is preferably 1-10 minutes, and washing temperature of acidic washing is preferably 40-60°C. In step (4), said ultrasonic water washing is aimed to remove the product of acidic washing on the surface of the metals or alloys, and preferably performed with distilled water for 2-10 minutes at room temperature.

In step (5), said neutralizing with basic solution means dipping in a basic solution to further remove the product of acidic washing. Said basic solution is water solution containing a strong base or a weak base, preferably is water solution of NaOH or Na₂C0₃; said basic solution has preferably a pH of 10-11. Said dipping time preferably is 3-10 minutes, dipping temperature preferably is at 50-60°C

Preferably, the surface treatment method for light metals or alloys thereof of the present invention comprises: step (1 ) mechanically grinding; (2) degreasing; (3) acidic washing; (4) ultrasonic water washing; and (5) neutralizing with a basic solution; (6) contacting treatment by using surface treatment solution for light metals or alloys thereof of the present invention to form a coating.

Wherein, the method and the preferable conditions for said steps (1 )-(6) are same as those of above-mentioned.

In the present invention, said light metals are those having a density less than 4.5 g/cm³, including aluminum, magnesium, or zinc, etc.

Said surface treatment method for light metals or alloys thereof of the present invention may also comprise water washing after the contacting treatment to remove the residue of the surface treatment solution from the surface of the light metals or alloys thereof. Preferably, time of water washing is 2-3. Preferably, water washing may be performed after each step of above steps (1 )-(6) for 2-3 times.

In the present invention, above preferable conditions may be combined at will to obtain various preferred embodiments.

The reagents and raw materials are commercially available.

The advantages of the present invention are as follows.

1. The present invention provides a surface treatment composition and a solution thereof suitable for a plurality of light metals or alloys thereof, said solution has a wide application range comprising magnesium alloys, zinc alloys, aluminum alloys, etc.

2. The surface treatment solution of the present invention can form a layer of even, dense vanadium-titanium coating layer, which has a good resistance to corrosion and a high adherence force with the painting coating to realize a good coating performance. The corrosion resistant test is performed on the light metals or alloys thereof treated with the surface treatment solution of the present invention with the salt spray test standard ASTM B117-03, after 48 hours corrosion, the maximum value of corrosion rate is only 0.3%, the coating performance is up to Level 0, obviously superior to the prior art.

3. The light metals or alloys thereof treated with the surface treatment solution of the present invention still exhibit a good conductivity.

4. The surface treatment method of the present invention has a wide application range, pH range of 4-11 , time of 2-11 minutes, and is applicable to both acidic and basic conditions.

5. The surface treatment composition and solution of the present invention has a simple formulation thus is easy to prepare, and contains no six-valence Cr and F thus is environment friendly; said surface treatment solution is stable and can be kept for more than 240 days at room temperature (20-40°C and more than 100 days below 0°C without deposit, produces less residue being able to be removed by water washing.

Specific Embodiments:

The present invention will be described in connection with examples, to which the present invention is not limited.

In the following examples, all the percentages of vanadium-containing compounds, titanium-containing compounds and phosphorus-containing compounds recited in the surface treatment solution formulation are mass percentage of corresponding vanadium, phosphorus or titanium element. For example, 0.1 % sodium metavandate means the mass percentage of the vanadium element in sodium metavandate relative to the surface treatment solution is 0.1 %. All the percentages recited for an organic acid means the mass percentage of the organic acid relative to the surface treatment solution.

Example 1

The formulation of the surface treatment composition: sodium metavandate, n-butyl titanate and lactic acid, wherein, the mass ratio of vanadium element to titanium element is 10:1 , and the mass ratio of oxygen element in the lactic acid to vanadium element is 1 :5.

The formulation of the surface treatment solution: 0.1 % sodium metavanadate, 0.01 % n-butyl titanate (vanadium elemen:titanium elemen = 10:1 ), 0.1 % lactic acid, pH = 8.

The surface treatment solution is prepared as follows: dissolving sodium metavanadate with 50%

NaOH solution by mass, and filtering off impurities, adding n-butyl titanate, citric acid and water, stirring, then adjusting pH to 8 with citric acid (1 % by mass).

Surface treatment method for the light metals alloys:

Magnesium-aluminum alloy AZ91 D is selected as the substrate material and treated by following steps:

(1 ) mechanically grinding: the method is performed by referring to a conventional method of the art;

(2) degreasing: washing with a basic solution for 10 minutes at 50°C. The formulation of the basic solution is: 5% NaOH solution by mass, pH 11 ;

(3) acidic washing: washing with an acidic solution for 10 minutes at 50°C. The formulation of the acidic solution is 1 % acetic acid water solution by mass, pH 5;

(4) ultrasonic water washing: performed in distilled water for 2 minutes at room temperature;

(5) neutralizing with a basic solution: dipping in a basic solution for 10 minutes at 50°C, wherein the formulation of the basic solution is: 5% Na₂C0₃ solution by mass, pH 10;

(6) coating forming: dipping the substrate in the surface treatment solution for 15 minutes at 60°C to obtain an even, dense, grey coating layer on the surface of the substrate, which exhibits a good corrosion resistance and adherence force.

Above surface treatment solution does not precipitate after 100 days and 240 days storage at 0°C and room temperature, respectively.

Example 2

The formulation of the surface treatment composition: sodium metavandate, n-butyl titanate, polyphosphoric acid and formic acid, wherein, the mass ratio of vanadium element to titanium element is 10:1 , and the mass ratio of vanadium element to phosphorus element is 10:1 , the mass ratio of oxygen element in formic acid to vanadium element is 1 :10.

The formulation of the surface treatment solution: 0.1 % sodium metavanadate, 0.01 % n-butyl titanate, 0.01 % polyphosphoric acid (vanadium element : titanium element = 10:1 ; vanadium element : phosphorus element = 10:1 ), 0.1 % formic acid, pH = 5.

The surface treatment solution is prepared as follows: dissolving sodium metavanadate with 50% NaOH solution by mass, and filtering off impurities, adding n-butyl titanate, polyphosphoric acid, formic acid and water, stirring, then adjusting pH to 5 with citric acid (1 % by mass).

Surface treatment method for the light metals alloys:

(3) acidic washing: washing with an acidic solution for 10 minutes at 50°C. The formulation of the acidic solution is 1 % acetic acid solution by mass, pH 5;

(5) neutralizing with a basic solution: dipping the substrate in a basic solution for 10 minutes at 50°C, wherein the formulation of the basic solution is: 5% Na₂C0₃ solution by mass, pH 10;

Above surface treatment solution does not precipitate after 60 days storage at 0°C and 40°C respectively.

Example 3

The formulation of the surface treatment composition: sodium metavandate, n-butyl titanate, polyphosphoric acid and acetic acid, wherein, the mass ratio of vanadium element to titanium element is 10:1 , and the mass ratio of vanadium element to phosphorus element is 10:1 , the mass ratio of oxygen element in acetic acid to vanadium element is 1 :9.

The formulation of the surface treatment solution: 1 % sodium metavanadate, 0.1 % n-butyl titanate, 0.1 % polyphosphoric acid (vanadium element : titanium element = 10:1 ; vanadium element : phosphorus element = 10:1 ), 0.5% acetic acid, pH = 7.6.

The surface treatment solution is prepared as follows: dissolving Ammonium metavanadate with 50% NaOH solution by mass, and filtering off impurities, adding n-butyl titanate, polyphosphoric acid, lactic acid and water, stirring, then adjusting pH to 7.6 with lactic acid.

Surface treatment method for the light metals alloys:

(3) acidic washing: washing with an acidic solution for 5 minutes at 50°C. The formulation of the acidic solution is 1 % acetic acid solution by mass, pH 5;

(4) ultrasonic water washing: performed in distilled water for 5 minutes at room temperature;

(6) coating forming: dipping the substrate in the surface treatment solution for 2 minutes at 40°C to obtain an even, dense, grey coating layer on the surface of the substrate, which exhibits a good corrosion resistance and adherence force.

Example 4

The formulation of the surface treatment composition: sodium metavandate, n-butyl titanate, polyphosphoric acid and citric acid, wherein, the mass ratio of vanadium element to titanium element is 1 :10, and the mass ratio of vanadium element to phosphorus element is 1 :100, the mass ratio of oxygen in citric acid to vanadium is 1 :20.

The formulation of the surface treatment solution: 0.01 % sodium metavanadate, 0.1 % n-butyl titanate, 1 % polyphosphoric acid (vanadium element : titanium element = 1 :10; vanadium element : phosphorus element = 1 :100), 0.01 % citric acid, pH = 7.1.

The surface treatment solution is prepared as follows: dissolving sodium metavanadate with 50% NaOH solution by mass, and filtering off impurities, adding n-butyl titanate, polyphosphoric acid, citric acid and water, stirring, then adjusting pH to 7.1 with lactic acid.

Surface treatment method for the light metals alloys:

(1 ) mechanically grinding: the method is performed by referring to a conventional method of the art; (2) degreasing: washing with a basic solution for 10 minutes at 50°C. The formulation of the basic solution is: 5% NaOH solution by mass, pH 11 ;

(3) acidic washing: washing with an acidic solution for 5 minutes at 50°C. The formulation of acidic solution is: 1 % by mass acetic acid solution, pH 5;

(4) ultrasonic water washing: performed in distilled water for 10 minutes at room temperature;

(5) neutralizing with a basic solution: dipping the substrate in a basic solution for 5 minutes at 50°C, the formulation of the basic solution is: 5% Na₂C0₃ solution by mass, pH 10;

(6) coating forming: dipping the substrate in the surface treatment solution for 30 minutes at 40°C to obtain an even, dense, grey coating layer on the surface of the substrate, which exhibits a good corrosion resistance and adherence force.

Example 5

The formulation of the surface treatment composition: sodium vandate, isopropyl titanate, polyphosphoric acid and lactic acid, wherein, the mass ratio of vanadium element to titanium element is 10:1 , and the mass ratio of vanadium element to phosphorus element is 1 :10, the mass ratio of oxygen element in lactic acid to vanadium element is 5.5:1 .

The formulation of the surface treatment solution: 0.1 % sodium vanadate, 0.01 % isopropyl titanate, 1 % polyphosphoric acid (vanadium element : titanium element = 10:1 ; vanadium element : phosphorus element = 1 :10), 0.2% lactic acid, pH = 5.5.

The surface treatment solution is prepared as follows: dissolving sodium vanadate with 50% NaOH solution, and filtering off impurities, adding isopropyl titanate, polyphosphoric acid, lactic acid and water, stirring, then adjusting pH to 5.5 with citric acid (1 % by mass).

Surface treatment method for the light metals alloys:

(2) degreasing: washing with a basic solution for 3 minutes at 50°C. The formulation of the basic solution is: 5% NaOH solution by mass, pH 11 ;

(3) acidic washing: washing with an acidic solution for 3 minutes at 50°C. The formulation of the acidic solution is: 1 % by mass acetic acid solution, pH 5;

(4) ultrasonic water washing: performed in distilled water for 4 minutes at room temperature;

(5) neutralizing with a basic solution: dipping the substrate in a basic solution for 6 minutes at 50°C, wherein the formulation of the basic solution is: 5% Na₂C0₃ solution by mass, pH 10;

(6) coating forming: dipping the substrate in the surface treatment solution for 15 minutes at 40°C to obtain an even, dense, grey coating layer on the surface of the substrate, which exhibits a good corrosion resistance and adherence force.

Above surface treatment solution does not precipitate after 60 days storage 0°C and 40°C, respectively.

Example 6

The formulation of the surface treatment composition: sodium metavandate, isopropyl titanate, polyphosphoric acid and formic acid, wherein, the mass ratio of vanadium element to titanium element is 100:1 , and the mass ratio of vanadium element to phosphorus element is 1 :1 , the mass ratio of oxygen element in formic acid to vanadium element is 4:1.

The formulation of the surface treatment solution: 0.1 % sodium metavanadate, 0.01 % isopropyl titanate, 0.1 % polyphosphoric acid (vanadium element : titanium element = 100:1 ; vanadium element : phosphorus element = 1 :1 ), 2% formic acid, pH = 9.

The surface treatment solution is prepared as follows: dissolving sodium metavanadate with 50% NaOH solution by mass, and filtering off impurities, adding isopropyl titanate, polyphosphoric acid, formic acid and water, stirring, then adjusting pH to 9 with NaOH (0.1 % by mass).

Surface treatment method for the light metals alloys:

(3) acidic washing: washing with an acidic solution for 5 minutes at 50°C. The formulation of acidic solution is: 1 % by mass acetic acid solution, pH 4;

(5) neutralizing with a basic solution: dipping the substrate in a basic solution for 3 minutes at 50°C, wherein the formulation of the basic solution is: 5% Na₂C0₃ solution by mass, pH 10;

(6) coating forming: dipping the substrate in the surface treatment solution for 5 minutes at 40°C to obtain an even, dense, grey coating layer on the surface of the substrate, which exhibits a good corrosion resistance and adherence force.

Example 7

The formulation of the surface treatment composition: sodium metavandate, titanium tetrachloride, polyphosphoric acid and citric acid, wherein, the mass ratio of vanadium element to titanium element is 10:1 , and the mass ratio of vanadium element to phosphorus element is 100:1 , the mass ratio of oxygen element in citric acid to vanadium element is 9:1 . The formulation of the surface treatment solution: 0.1 % sodium metavanadate, 0.01 % titanium tetrachloride, 0.001 % polyphosphoric acid (vanadium element : titanium element = 10:1 ; vanadium element : phosphorus element = 100:1 ), 1 % citric acid, pH = 6.5.

NaOH solution by mass, and filtering off impurities, adding titanium tetrachloride, polyphosphoric acid, citric acid and water, stirring, then adjusting pH to 6.5 with citric acid.

Surface treatment method for the light metals alloys:

(6) coating forming: dipping the substrate in the surface treatment solution for 25 minutes at 40°C to obtain an even, dense, grey coating layer on the surface of the substrate, which exhibits a good corrosion resistance and adherence force.

Example 8

The formulation of the surface treatment composition: sodium metavandate, isopropyl titanate, polyphosphoric acid and lactic acid, wherein, the mass ratio of vanadium element to titanium element is 1 :100, and the mass ratio of vanadium element to phosphorus element is 1 :50, the mass ratio of oxygen element in lactic acid to vanadium element is 5:1 .

The formulation of the surface treatment solution: 0.005% sodium metavanadate, 0.5% isopropyl titanate, 0.25% polyphosphoric acid (vanadium element : titanium element = 1 :100; vanadium element : phosphorus element = 1 :50), 0.5% lactic acid, pH = 5.

The surface treatment solution is prepared as follows: dissolving sodium metavanadate with 50% NaOH solution by mass, and filtering off impurities, adding isopropyl titanate, polyphosphoric acid, lactic acid and water, stirring, then adjusting pH to 5 with citric acid (1 % by mass).

Surface treatment method for the light metals alloys:

Magnesium-aluminum alloy AZ91 D is selected as the substrate material and treated by following steps: (1 ) mechanically grinding: the method is performed by referring to a conventional method of the art;

(4) ultrasonic water washing: performed in distilled water for 6 minutes at room temperature;

(5) neutralizing with a basic solution: dipping the substrate in a basic solution for 5 minutes at 50°C, wherein the formulation of the basic solution is: 5% Na₂C0₃ solution by mass, pH 10;

(6) coating forming: dipping the substrate in the surface treatment solution for 60 minutes at 40°C to obtain an even, dense, grey coating layer on the surface of the substrate, which exhibits a good corrosion resistance and adherence force.

Example 9

The formulation of the surface treatment composition: sodium metavandate, isopropyl titanate, polyphosphoric acid and lactic acid, wherein, the mass ratio of vanadium element to titanium element is 1 :50, and the mass ratio of vanadium element to phosphorus element is 1 :100, the mass ratio of oxygen element in lactic acid to vanadium element is 3:1 .

The formulation of the surface treatment solution: 0.001 % sodium metavanadate, 0.05% isopropyl titanate, 0.1 % polyphosphoric acid (vanadium element : titanium element = 1 :50; vanadium element : phosphorus element = 1 :100), 0.5% lactic acid, pH = 8.

The surface treatment solution is prepared as follows: dissolving sodium metavanadate with 50% NaOH solution by mass, and filtering off impurities, adding isopropyl titanate, polyphosphoric acid, lactic acid and water, stirring, then adjusting pH to 8 with citric acid (1 % by mass).

Surface treatment method for the light metals alloys:

(2) degreasing: washing with a basic solution for 6 minutes at 50°C. The formulation of the basic solution is: 5% NaOH solution by mass, pH 11 ;

(4) ultrasonic water washing: performed in distilled water for 8 minutes at room temperature;

(5) neutralizing with a basic solution: dipping the substrate in a basic solution for 3 minutes at 50°C, wherein the formulation of the basic solution is: 5% Na₂C0₃ solution by mass, pH 10; (6) coating forming: dipping the substrate in the surface treatment solution for 40 minutes at 40°C to obtain an even, dense, grey coating layer on the surface of the substrate, which exhibits a good corrosion resistance and adherence force.

Example 10

The formulation of the surface treatment composition: ammonium metavandate, titanate coupling agent TC-F, polyphosphoric acid and lactic acid, wherein, the mass ratio of vanadium element to titanium element is 50:1 , and the mass ratio of vanadium element to phosphorus element is 1 :10, the mass ratio of oxygen element in lactic acid to vanadium element is 1 :5.

The formulation of the surface treatment solution: 0.005% ammonium metavanadate, 0.001 % titanate coupling agent TC-F, 0.05% polyphosphoric acid (vanadium element : titanium element =

50:1 ; vanadium element : phosphorus element = 1 :10), 0.01 % lactic acid, pH = 11.

The surface treatment solution is prepared as follows: dissolving ammonium metavanadate with

50% NaOH solution, and filtering off impurities, adding titanate coupling agent TC-F, polyphosphoric acid, lactic acid and water, stirring, then adjusting pH to 11 with NaOH (0.1 % by mass).

Surface treatment method for the light metals alloys:

Example 11

The formulation of the surface treatment composition: ammonium metavandate, titanate coupling agent TC-70, polyphosphoric acid and citric acid, wherein, the mass ratio of vanadium element to titanium element is 10:1 , and the mass ratio of vanadium element to phosphorus element is

10:1 , the mass ratio of oxygen element in citric acid to vanadium element is 7:1.

The formulation of the surface treatment solution: 1 % ammonium metavanadate, 0.1 % titanate coupling agent TC-70, 0.1 % polyphosphoric acid (vanadium element : titanium element = 10:1 ; vanadium element : phosphorus element = 10:1 ), 2% citric acid, pH = 7.6.

The surface treatment solution is prepared as follows: diluting the surface treatment composition with deioned water by 1 :100, then adjusting pH to 7.6 with lactic acid to obtain the surface treatment solution.

Surface treatment method for the light metals alloys:

(2) degreasing: washing with a basic solution for 5 minutes at 40°C. The formulation of the basic solution is: 5% NaOH solution by mass, pH 10;

(3) acidic washing: washing with an acidic solution for 1 minutes at 40°C. The formulation of the acidic solution is: 1 % by mass acetic acid solution, pH 6;

(5) neutralizing with a basic solution: dipping the substrate in a basic solution for 10 minutes at 60°C, wherein the basic solution is 50% NaOH, pH 11 ;

(6) coating forming: dipping the substrate in the surface treatment solution for 25 minutes at 60°C to obtain an even, dense, grey coating layer on the surface of the substrate, which exhibits a good corrosion resistance and adherence force.

Example 12

The formulation of the surface treatment composition: ammonium metavandate, tetraethyl titanate, polyphosphoric acid and lactic acid, wherein, the mass ratio of vanadium element to titanium element is 2:1 , and the mass ratio of vanadium element to phosphorus element is 10:1 , the mass ratio of oxygen element in lactic acid to vanadium element is 6:1 .

The formulation of the surface treatment solution: 10% ammonium metavanadate, 5% tetraethyl titanate, 1 % polyphosphoric acid (vanadium element : titanium element = 2:1 ; vanadium element : phosphorus element = 10:1 ), 3% lactic acid, pH = 7.3.

The surface treatment solution is prepared as follows: dissolving ammonium metavanadate with 50% NaOH solution by mass, and filtering off impurities, adding tetraethyl titanate, polyphosphoric acid, lactic acid and water, stirring, then adjusting pH to7.3 with citric acid (0.1 % by mass).

Surface treatment method for the light metals alloys:

(2) degreasing: washing with a basic solution for 5 minutes at 80°C. The formulation of the basic solution is: 5% NaOH solution by mass, pH 11 ;

(3) acidic washing: washing with an acidic solution for 1 minutes at 60°C. The formulation of the acidic solution is: 1 % by mass acetic acid solution, pH 3;

(5) neutralizing with a basic solution: dipping the substrate in a basic solution for 10 minutes at 60°C, wherein the formulation of the basic solution is: 5% Na₂C0₃ solution by mass, pH 10;

(6) coating forming: dipping the substrate in the surface treatment solution for 2 minutes at 40 to obtain an even, dense, grey coating layer on the surface of the substrate, which exhibits a good corrosion resistance and adherence force.

Above surface treatment solution does not precipitate after 60 days storage 0 and 40 , respectively.

Example 13

The formulation of the surface treatment composition: sodium metavandate, titanate coupling agent TA-13, polyphosphoric acid and citric acid, wherein, the mass ratio of vanadium element to titanium element is 10:1 , and the mass ratio of vanadium element to phosphorus element is 10:1 , the mass ratio of oxygen element in lactic acid to vanadium element is 8:1 .

The formulation of the surface treatment solution: 0.1 % sodium metavanadate, 0.01 % titanate coupling agent TA-13, 0.01 % polyphosphoric acid (vanadium element : titanium element = 10:1 ; vanadium element : phosphorus element = 10:1 ), 5% lactic acid, pH = 8.

NaOH solution by mass, and filtering off impurities, adding titanate coupling agent TA-13, polyphosphoric acid, lactic acid and water, stirring, then adjusting pH to 8 with citric acid (1 % by mass).

Surface treatment method for the light metals alloys:

Aluminum alloys AD12 is selected as the substrate material and treated by following steps:

(2) degreasing: washing with a basic solution for 10 minutes at 50 . The formulation of the basic solution is: 5% NaOH solution by mass, pH 11 ;

(3) acidic washing: washing with an acidic solution for 10 minutes at 50 . The formulation of the acidic solution is 1 % acetic acid solution by mass, pH 5;

(5) neutralizing with a basic solution: dipping the substrate in a basic solution for 10 minutes at 50 , wherein the formulation of the basic solution is: 5% Na₂C0₃ solution by mass, pH 10;

(6) coating forming: dipping the substrate in the surface treatment solution for 15 minutes at 60 to obtain an even, dense, grey coating layer on the surface of the substrate, which exhibits a good corrosion resistance and adherence force.

Example 14

The formulation of the surface treatment composition: Ammonium metavandate, titanate TC-13, polyphosphoric acid and lactic acid, wherein, the mass ratio of vanadium element to titanium element is 10:1 , and the mass ratio of vanadium element to phosphorus element is 10:1 , the mass ratio of oxygen element in lactic acid to vanadium element is 10:1.

The formulation of the surface treatment solution: 1 % Ammonium metavanadate, 0.1 % titanate TA-13, 0.1 % polyphosphoric acid (vanadium element : titanium element = 10:1 ; vanadium element : phosphorus element = 10:1 ), 5% lactic acid, pH = 7.9.

The surface treatment solution is prepared as follows: dissolving Ammonium metavanadate with 50% NaOH solution by mass, and filtering off impurities, adding titanate TC-13, polyphosphoric acid, lactic acid and water, stirring, then adjusting pH to 7.9 with citric acid (1 % by mass).

Surface treatment method for the light metals alloys:

(2) degreasing: washing with a basic solution for 5 minutes at 50 . The formulation of the basic solution is: 5% NaOH solution by mass, pH 11 ;

(3) acidic washing: washing with an acidic solution for 5 minutes at 50 . The formulation of acidic solution is: 1 % by mass acetic acid solution, pH 5;

(5) neutralizing with a basic solution: dipping the substrate in a basic solution for 10 minutes at 50 , wherein the basic solution is: 5% Na₂C0₃ solution by mass, pH 10;

Above surface treatment solution does not precipitate after 60 days storage 0 and 40 , respectively. Example 15

The formulation of the surface treatment composition: sodium metavandate, titanate TC-13, polyphosphoric acid and lactic acid, wherein, the mass ratio of vanadium element to titanium element is 10:1 , and the mass ratio of vanadium element to phosphorus element is 10:1 , the mass ratio of oxygen element in lactic acid to vanadium element is 6:5.

The formulation of the surface treatment solution: 0.1 % sodium metavanadate, 0.01 % titanate TC-13, 0.01 % polyphosphoric acid (vanadium element : titanium element = 10:1 ; vanadium element : phosphorus element = 10:1 ), 0.5% lactic acid, pH = 8.

The surface treatment solution is prepared as follows: dissolving sodium metavanadate with 50% NaOH solution by mass, and filtering off impurities, adding titanate TC-13, polyphosphoric acid, lactic acid and water, stirring, then adjusting pH to 11 with NaOH (0.1 % by mass).

Surface treatment method for the light metals alloys:

Zinc alloy Z8 is selected as the substrate material and treated by following steps:

(5) neutralizing with a basic solution: dipping the substrate in a basic solution for 10 minutes at 50 , the formulation of the basic solution is: 5% Na₂C0₃ solution by mass, pH 10;

Example 16

The formulation of the surface treatment composition: ammonium metavandate, titanate TC-13, polyphosphoric acid and lactic acid, wherein, the mass ratio of vanadium element to titanium element is 10:1 , and the mass ratio of vanadium element to phosphorus element is 10:1 , the mass ratio of oxygen element in lactic acid to vanadium element is 16:5.

The formulation of the surface treatment solution: 1 % ammonium metavanadate, 0.1 % titanate TC-13, 0.1 % polyphosphoric acid (vanadium element : titanium element = 10:1 ; vanadium element : phosphorus element = 10:1 ), 1 % lactic acid, pH = 10.

The surface treatment solution is prepared as follows: dissolving ammonium metavanadate with 50% NaOH solution by mass, and filtering off impurities, adding titanate TC-13, polyphosphoric acid, lactic acid and water, stirring, then adjusting pH to 10 with NaOH (0.1 % by mass).

Surface treatment method for the light metals alloys:

Example 17

The formulation of the surface treatment composition: ammonium metavandate, titanate TC-14, polyphosphoric acid and lactic acid, wherein, the mass ratio of vanadium element to titanium element is 5:1 , and the mass ratio of vanadium element to phosphorus element is 8:1 , the mass ratio of oxygen element in lactic acid to vanadium element is 36:5.

The formulation of the surface treatment solution: 0.02% ammonium metavanadate, 0.001 % titanate TC-14, 0.1 % polyphosphoric acid (vanadium element : titanium element = 10:1 ; vanadium element : phosphorus element = 100:1 ), 0.8% lactic acid, pH = 6.5.

The surface treatment solution is prepared as follows: dissolving Vanadium oxide with 50% NaOH solution by mass, and filtering off impurities, adding ammonium metavanadate, titanate TC-14, polyphosphoric acid, lactic acid and water, stirring, then adjusting pH to 6.5 with citric acid (1 % by mass).

Surface treatment method for the light metals alloys:

Metal aluminum is selected as the substrate material and treated by following steps:

(3) acidic washing: washing with an acidic solution for 5 minutes at 50 . The formulation of acidic solution is: 1 % by mass acetic acid solution, pH 5; (4) ultrasonic water washing: performed in distilled water for 10 minutes at room temperature;

(5) neutralizing with a basic solution: dipping the substrate in a basic solution for 3 minutes at 50 , wherein the formulation of the basic solution is: 5% Na₂C0₃ solution by mass, pH 10;

(6) coating forming: dipping the substrate in the surface treatment solution for 25 minutes at 40 to obtain an even, dense, grey coating layer on the surface of the substrate, which exhibits a good corrosion resistance and adherence force.

Effect Example:

The metal samples obtained after surface treatment in Examples 1-17 are tested for corrosion resistance, coating-coating adherence force and surface resistance etc. The test results are listed in table 1 .

Corrosion resistance test:

5% NaCI solution is sprayed on the treated metal surface, and the corrosion ratios are observed on the metal surface after 8 hours, 24 hours, 48 hours. The corrosion ratio is expressed as follows:

Corrosion ratio = (the corrupted region area)/(magnesium alloy surface area)) ^χ 100% Coating-coating adherence force test:

According the method described in GB/T 9286-1998 (i.e., ISO 2409:2007), coating-coating adherence forces are tested. The metal samples obtained after surface treatment in Examples 1-17 are sprayed with powders; dried; and scored with 6 parallel cutting lines spaced away 1 mm on the coating surfaces, deep to the substrate; then scored with same number of parallel cutting lines orthogonal to those previously scored.

Strips are stuck to the grids between scored lines and peeled off at 60° in 5 minutes, after which, the coating-coating adherence forces are valuated by Levels 0-5 through observing the adherence status of the coating layer, wherein Level 0 is best and indicates that the edge of the scored line is smooth and no grid flakes off; while Level 5 is poorest.

Surface resistance test:

A multimeter is employed to test the surface resistance of the metal samples obtained after surface treatment in Examples 1 -17.

The results are shown in Table 1 . Example Corrosion ratio % Adherence Surface

8 hours 24 hours 48 hours force level resistance/Ω

1 0.03 0.1 0.3 0 1.05

2 0.03 0.03 0.1 0 0.09

3 0.03 0.1 0.1 0 0.08

4 0.03 0.03 0.03 0 0.12

5 0.03 0.03 0.1 0 0.15

6 0.03 0.1 0.1 0 0.09

7 0.03 0.03 0.1 0 0.21

8 0.03 0.03 0.1 0 0.35

9 0.03 0.03 0.1 0 0.17

10 0.03 0.1 0.3 0 0.19

11 0.03 0.03 0.1 0 0.67

12 0.03 0.1 0.3 0 0.56

13 0.03 0.3 0.1 0 0.22

14 0.03 0.3 0.1 0 0.89

15 0.03 0.1 0.3 0 0.66

16 0.03 0.03 0.1 0 1.02

17 0.03 0.1 0.3 0 0.23

As can seen from Table 1 , the magnesium alloys, aluminum alloys and zinc alloys treated using the surface treatment solution of the present invention have good corrosion resistance, corrosion ratio after 48 hours spray test is only 0.1-0.3%, significantly better than 3% in the prior art. The coating-coating adherence force is very good and meets the requirement for Level 0 according to corresponding national standard of China. The surface resistance of the alloy only is 0.09-1 .02Ω, which makes the alloys keeps a good conductivity. In contrast, the surface resistance rises of the alloy to 3Ω after surface treatment in prior art.

Claims

22 Claims

1 . A surface treatment composition for light metals or alloys thereof, characterized in that the composition comprises a titanium-containing compound, a vanadium-containing compound, and an organic acid, wherein the organic acid contains 1 -100 carbon atoms, 2-50 oxygen atoms.

2. Surface treatment composition according to Claim 1 , characterized in that the titanium-containing compound is one or more of titanium oxide, titanic acid, titanate, and alkoxy compound of titanium; the vanadium-containing compound is one or more of vanadium oxide, vanadic acid, vanadate, metavanadic acid, and metavanadate; the organic acid is one or more of formic acid, acetic acid, citric acid, tannic acid and lactic acid.

3. Surface treatment composition according to Claim 1 or 2, characterized in that mass ratio of vanadium element of the vanadium-containing compound to titanium element of the titanium-containing compound is between 1 :100 to 100:1 ; and the mass ratio of oxygen element of the organic acid to vanadium element of the vanadium-containing compound is 1 :20-16:1.

4. Surface treatment composition according to any one of Claims 1-3, characterized in that the surface treatment composition for light metals or alloys thereof may also comprise a phosphorus-containing compound.

5. Surface treatment composition according to any one of Claims 1-4, characterized in that the phosphorus-containing compound is one or more of phosphoric acid and salts thereof, metaphosphoric acid and salts thereof, phosphorous acid and salts thereof, phosphinic acid and salts thereof and polyphosphoric acid and salts thereof.

6. Surface treatment composition according to any one of Claims 1-5, characterized in that mass ratio of vanadium element of the vanadium-containing compound to phosphorus element of the phosphorus-containing compound is 1 :100-100:1.

7. A surface treatment solution for light metals or alloys thereof, characterized in that the solution comprises titanium element in water-soluble form, vanadium element in water-soluble form, an organic acid and water, wherein the organic acid has 1-100 carbon atoms, and 2-50 oxygen atoms.

8. Surface treatment solution according to Claim 7, characterized in that the titanium element in water-soluble form is present in titanium ion and/or titanate ion in the solution. 23

9. Surface treatment solution according to Claim 7 or 8, characterized in that the content of titanium element in water-soluble form is 0.0001 -5% of the surface treatment solution by mass.

10. Surface treatment solution according to any one of Claims 7-9, characterized in that the content of titanium element in water-soluble form is 0.001-0.1 % of the surface treatment solution by mass.

11 . Surface treatment solution according to any one of Claims 7-10, characterized in that the vanadium element in water-soluble form is present in one or more of vanadium ion, vanadate ion and metavanadate ion in the solution.

12. Surface treatment solution according to any one of Claims 7-11 , characterized in that the content of the vanadium element in water-soluble form is 0.001 -10% of the surface treatment solution by mass.

13. Surface treatment solution according to any one of Claims 7-12, characterized in that the content of the vanadium element in water-soluble form is 0.01 -0.1 % of the surface treatment solution by mass.

14. Surface treatment solution according to any one of Claims 7-13, characterized in that the organic acid is one or more of formic acid, acetic acid, citric acid, tannic acid and lactic acid.

15. Surface treatment solution according to any one of Claims 7-14, characterized in that the content of the organic acid is 0.001 -1 % of the surface treatment solution by mass.

16. Surface treatment solution according to any one of Claims 7-15, characterized in that mass ratio of vanadium element in water-soluble form to titanium element in water-soluble form is 1 :100 to 100:1 ; and mass ratio of oxygen element of the organic acid to the vanadium element in water-soluble form is 1 :20-16:1 .

17. Surface treatment solution according to any one of Claims 7-16, characterized in that the surface treatment solution for light metals or alloys thereof of the present invention contains phosphorus element in water-soluble form.

18. Surface treatment solution for light metals or alloys thereof according to any one of Claims 7-17, characterized in that the phosphorus element in water-soluble form is present in one or more of phosphate ion, metaphosphate ion, phosphite ion, or phosphinate ion in the solution. 24

19. Surface treatment solution according to any one of Claims 7-18, characterized in that content of the phosphorus element in water-soluble form is 0.0001-1 % of the surface treatment solution by mass.

20. Surface treatment solution according to any one of Claims 7-19, characterized in that content of the phosphorus element in water-soluble form is 0.001 -0.1 % of the surface treatment solution by mass.

21. Surface treatment solution according to any one of Claims 7-20, characterized in that mass ratio of the vanadium element in water-soluble form to the phosphorus element in water-soluble form is 1 :100-100:1.

22. Surface treatment solution according to any one of Claims 7-21 , characterized in that pH value of the surface treatment solution is 4-11.

23. Surface Treatment solution according to any one of claims 7 -21 , characterized in that the solution contains not more than 1 ppm of chromium and/or fluorine, more preferably contains no source of chromium and/or fluorine.

24. A surface treatment method for light metals or alloys thereof comprises the following step: pre-treating the light metals or alloys thereof, then contacting with the surface treatment solution according to any one of Claims 7-23 to form a coating.

25. The surface treatment method according to Claim 24, characterized in that the contacting treatment comprises dipping, coating, spray coating, rinsing; the contacting treatment time is 2-60 minutes and the contacting treatment temperature is 25-60°C.

26. The surface treatment method according to Claim 22 or 25, characterized in that the pre-treatment comprises step (1 ) mechanically grinding; (2) degreasing; (3) acidic washing; (4) ultrasonic water washing; and (5) neutralizing with a basic solution in this order.

27. The surface treatment method according to Claim 26, characterized in that,

in step (2), the degreasing is washing with a basic solution; pH of the basic solution is 10-11 ; washing time with the basic solution is 3-10 minutes; and washing temperature with the basic solution is 40-80 ;

in step (3), the acidic washing employs an acidic solution; pH of the acidic solution is 3-6; washing time of the acidic washing is 1 -10 minutes; and washing temperature of the acidic washing is 40-60°C. 25

in step (4), the ultrasonic water washing is performed with distilled water for 2-10 minutes; in step (5), the neutralizing with basic solution is dipping in a basic solution; pH of basic solution is 10-11 ; dipping time is 3-10 minutes; dipping temperature is 50-60°C.