阅读说明：本技术 一种耐高盐雾镁合金皮膜剂及其制备方法 (High-salt-spray-resistant magnesium alloy coating agent and preparation method thereof ) 是由 邓剑明 于 2020-12-17 设计创作，主要内容包括：一种耐高盐雾镁合金皮膜剂及其制备方法,涉及金属表面处理技术领域；包括如下质量分数的组分：磷酸3-10％；碳酸钙1-8％；硝酸钡0.5-5％；磷酸二氢铵1-5％；磷酸二氢锰1-8％；络合剂0.5-2％；余量为水。本发明的一种耐高盐雾镁合金皮膜剂,通过钙盐、钡盐和络合剂的合理配比,能在镁合金表面形成均匀、细致、耐蚀性好的复合膜层,且膜层厚、耐高盐雾性能优越,该镁合金皮膜剂适用于镁合金脱脂表调后快速化成上膜应用。(A high-salt-spray-resistant magnesium alloy coating agent and a preparation method thereof relate to the technical field of metal surface treatment; the composition comprises the following components in percentage by mass: 3-10% of phosphoric acid; 1-8% of calcium carbonate; 0.5 to 5 percent of barium nitrate; 1-5% of ammonium dihydrogen phosphate; 1-8% of manganese dihydrogen phosphate; 0.5-2% of complexing agent; the balance being water. According to the high-salt-spray-resistant magnesium alloy coating agent, a uniform, fine and good-corrosion-resistance composite film can be formed on the surface of a magnesium alloy through reasonable proportioning of the calcium salt, the barium salt and the complexing agent, the film is thick, the high-salt-spray-resistant performance is excellent, and the magnesium alloy coating agent is suitable for being quickly formed into a coating after the magnesium alloy is degreased and regulated.)

1. The high-salt-spray-resistant magnesium alloy coating agent is characterized by comprising the following components in percentage by mass:

3-10% of phosphoric acid; 1-8% of calcium carbonate; 0.5 to 5 percent of barium nitrate;

1-5% of ammonium dihydrogen phosphate; 1-8% of manganese dihydrogen phosphate; 0.5-2% of complexing agent;

the balance of water.

2. The high-salt-spray-resistant magnesium alloy coating agent of claim 1, which comprises the following components in percentage by mass:

5-8% of phosphoric acid; 3-5% of calcium carbonate; 1-3% of barium nitrate;

1-3% of ammonium dihydrogen phosphate; 4-6% of manganese dihydrogen phosphate; 0.5 to 1.5 percent of complexing agent;

the balance of water.

3. The high-salt-spray-resistant magnesium alloy coating agent as claimed in claim 1 or 2, wherein: the complexing agent is EDTA-2 Na.

4. The high salt spray resistant magnesium alloy coating agent of claim 3, wherein: the mass ratio of the calcium carbonate to the barium nitrate to the EDTA-2Na is 4-4.5:2-2.5: 1.

5. The high-salt-spray-resistant magnesium alloy coating agent of claim 1, wherein: also comprises 0.1-0.3% of accelerator.

6. The high salt spray resistant magnesium alloy coating agent of claim 5, wherein: the promoter is sodium metavanadate.

7. The high-salt-spray-resistant magnesium alloy coating agent of claim 1, wherein: the composite material comprises the following components in percentage by mass:

5-8% of phosphoric acid; 3-5% of calcium carbonate; 1-3% of barium nitrate;

2% of ammonium dihydrogen phosphate; 4-6% of manganese dihydrogen phosphate; EDTA-2Na 1%;

the balance being water.

8. The preparation method of the high-salt-spray-resistant magnesium alloy coating agent as claimed in any one of claims 1 to 7, characterized by comprising the following steps:

1) preparing raw materials according to the formula amount;

2) adding a proper amount of water and phosphoric acid into the reaction kettle, adding calcium carbonate, and stirring until the calcium carbonate is completely dissolved;

3) sequentially adding barium nitrate, ammonium dihydrogen phosphate, manganese dihydrogen phosphate and EDTA-2Na, stirring until the barium nitrate, the ammonium dihydrogen phosphate, the manganese dihydrogen phosphate and the EDTA-2Na are completely dissolved, adding water to a constant volume, and obtaining the high-salt-spray-resistant magnesium alloy coating agent.

9. The preparation method of the high-salt-spray-resistant magnesium alloy coating agent of claim 8, characterized by comprising the following steps: in the step 3), 0.2% of ammonium metavanadate is added into the solution with constant volume.

Technical Field

The invention belongs to the technical field of metal surface treatment, and particularly relates to a high-salt-spray-resistant magnesium alloy coating agent and a preparation method thereof.

Background

Magnesium is extremely active in metallic properties and has a low electrode potential, and thus has extremely high chemical and electrochemical activity. Galvanic corrosion of magnesium alloys in contact with other metals generally occurs; the surfaces of magnesium and magnesium alloys are very susceptible to atmospheric corrosion in air. Therefore, the corrosion problem of the magnesium alloy is solved, and the beautifying and decorating functions and the service life of the magnesium alloy are met, so that the treatment of the surface of the magnesium alloy is very necessary.

At present, the coating agent for treating magnesium alloy generally uses a single calcium salt or manganese salt, such as a magnesium alloy coating agent with application number CN201310211596.5, and a high corrosion-resistant coating agent with application number CN201611182564.7, and the like, and the magnesium alloy coating mechanism using calcium salt and acid calcium salt is to make calcium phosphate deposit and cover on the surface of magnesium alloy to form a protective film by oxidation-reduction reaction under the conditions of acidity and matching with an oxidant. This skin film agent has the following disadvantages:

1. the water solubility of the acid calcium salt is poor, and the proportion of the added phosphoric acid is high during batch production, so that the acidity in the formula is high; 2. the formed film is uneven and fine, and the appearance color is darker; 3. the salt spray resistance is poor.

Disclosure of Invention

In order to overcome the defects of the prior art, one of the purposes of the invention is to provide a high-salt-spray-resistant magnesium alloy coating agent which can form a uniform, fine and good-corrosion-resistance composite film layer on the surface of a magnesium alloy, and has the advantages of thick film layer and excellent high-salt-spray-resistance performance.

The second purpose of the invention is to provide a preparation method of the high-salt-spray-resistant magnesium alloy coating agent, which is simple, low in toxicity and easy to implement.

One of the purposes of the invention is realized by adopting the following technical scheme:

the high-salt-spray-resistant magnesium alloy coating agent comprises the following components in percentage by mass:

3-10% of phosphoric acid; 1-8% of calcium carbonate; 0.5 to 5 percent of barium nitrate;

1-5% of ammonium dihydrogen phosphate; 1-8% of manganese dihydrogen phosphate; 0.5-2% of complexing agent;

the balance of water.

Further, the composition comprises the following components in percentage by mass:

5-8% of phosphoric acid; 3-5% of calcium carbonate; 1-3% of barium nitrate;

1-3% of ammonium dihydrogen phosphate; 4-6% of manganese dihydrogen phosphate; 0.5 to 1.5 percent of complexing agent;

the balance of water.

Further, the complexing agent is EDTA-2 Na. EDTA-2Na and partial Mg in working solution of coating agent²⁺Complexing and reducing film-forming substance CaMg₂(PO₄)₂And (4) generating.

Further, the mass ratio of the calcium carbonate to the barium nitrate to the EDTA-2Na is 4-4.5:2-2.5: 1. The composite film layer generated by the reaction under the proportion has more excellent comprehensive performance, and EDTA-2Na and the working solution of the coating agentPart of Mg²⁺Complexing and reducing film-forming substance CaMg₂(PO₄)₂The uniform and stable Ca with a thick film layer is formed on the surface of the magnesium alloy₃(PO₄)₂And form Ba₃(PO₄)₂Ca can be compensated by fine film layer₃(PO₄)₂The film layer is loose and porous, and the formed composite film layer is thick, fine, good in corrosion resistance and excellent in high-salt-spray resistance.

In one step, 0.1-0.3% of accelerator is also included.

Further, the promoter is sodium metavanadate. Sodium metavanadate as an accelerator can improve the reaction rate of forming the composite film layer.

Further, the composite material comprises the following components in percentage by mass:

5-8% of phosphoric acid; 3-5% of calcium carbonate; 1-3% of barium nitrate;

2% of ammonium dihydrogen phosphate; 4-6% of manganese dihydrogen phosphate; EDTA-2Na 1%;

the balance being water.

The second purpose of the invention is realized by adopting the following technical scheme:

the preparation method of the high-salt-spray-resistant magnesium alloy coating agent comprises the following steps:

1) preparing raw materials according to the formula amount;

2) adding a proper amount of water and phosphoric acid into the reaction kettle, adding calcium carbonate, and stirring until the calcium carbonate is completely dissolved;

3) sequentially adding barium nitrate, ammonium dihydrogen phosphate, manganese dihydrogen phosphate and EDTA-2Na, stirring until the barium nitrate, the ammonium dihydrogen phosphate, the manganese dihydrogen phosphate and the EDTA-2Na are completely dissolved, adding water to a constant volume, and obtaining the high-salt-spray-resistant magnesium alloy coating agent.

Further, in the step 3), 0.2% of ammonium metavanadate is added into the solution after the volume fixing.

Further, the mass ratio of the calcium carbonate to the barium nitrate to the EDTA-2Na is 4-4.5:2-2.5: 1.

Compared with the prior art, the invention has the beneficial effects that:

the invention relates to a high-salt-spray-resistant magnesium alloyGold coating agent, EDTA-2Na and partial Mg in working solution of coating agent²⁺Complexing and reducing film-forming substance CaMg₂(PO₄)₂The uniform and stable Ca with a thick film layer is formed on the surface of the magnesium alloy₃(PO₄)₂And form Ba₃(PO₄)₂Ca can be compensated by fine film layer₃(PO₄)₂The film layer is loose and porous, and a composite film layer with thick film layer, fineness, good corrosion resistance and excellent high-salt-spray resistance is formed; through the reasonable proportion of calcium salt, barium salt and complexing agent, a uniform, fine and good-corrosion-resistance composite film can be formed on the surface of the magnesium alloy, the film is thick, and the high-salt-spray-resistance performance is superior.

The preparation method of the high-salt-spray-resistant magnesium alloy coating agent is simple, low in toxicity and easy to implement.

Detailed Description

The present invention is further described below with reference to specific embodiments, and it should be noted that, without conflict, any combination between the embodiments or technical features described below may form a new embodiment.

Example 1

The high-salt-spray-resistant magnesium alloy coating agent comprises the following components in percentage by mass:

5% of phosphoric acid, 3% of calcium carbonate, 1% of barium nitrate, 2% of ammonium dihydrogen phosphate, 4% of manganese dihydrogen phosphate, 1% of EDTA-2Na and 84% of purified water.

The preparation method of the high-salt-spray-resistant magnesium alloy coating agent comprises the following steps:

1) preparing raw materials according to the formula amount;

2) adding a proper amount of water and phosphoric acid into the reaction kettle, adding calcium carbonate, and stirring until the calcium carbonate is completely dissolved;

3) sequentially adding barium nitrate, ammonium dihydrogen phosphate, manganese dihydrogen phosphate and EDTA-2Na, stirring until the barium nitrate, the ammonium dihydrogen phosphate, the manganese dihydrogen phosphate and the EDTA-2Na are completely dissolved, adding water to a constant volume, and obtaining the high-salt-spray-resistant magnesium alloy coating agent.

100g of the prepared high-salt-spray-resistant magnesium alloy coating agent is weighed, 900g of purified water is added to prepare working solution, and 2g of sodium metavanadate is added into the working solution to carry out a coating formation test.

Principle of formulation technology

According to the theory of oxidation-reduction reaction in chemistry, the film forming reaction of magnesium alloy in magnesium alloy coating agent can be considered as the following process:

Mg-2e^-→Mg²⁺

Ba²⁺+Mg²⁺+Ca(H₂PO₄)₂+2e^-→Ca₃(PO₄)₂+CaMg₂(PO₄)₂+Ba₃(PO₄)₂+H₂

among the film-forming substances, Ca₃(PO₄)₂The film layer is thick, the color is gray, and the film layer is loose, porous and not fine enough. CaMg₂(PO₄)₂Because the magnesium phosphate is calcium phosphate, the magnesium alloy has poor corrosion resistance on the surface of the magnesium alloy and is black in color. Ba₃(PO₄)₂Ca can be compensated by fine film layer₃(PO₄)₂The film layer is loose and porous, has white color, but is thin.

By the reaction principle, the first reaction is that metal Mg loses electrons in the magnesium alloy coating agent to form Mg²⁺Therefore, the whole working solution of the magnesium alloy coating agent contains a large amount of Mg²⁺In order to reduce CaMg₂(PO₄)₂A certain amount of metal complexing agent EDTA-2Na, EDTA-2Na and partial Mg in the working solution of the coating agent are added²⁺Complexing and reducing film-forming substance CaMg₂(PO₄)₂And (4) generating.

And according to the chemical reaction equilibrium, Mg is generated as the reaction proceeds²⁺Complexation and consumption of, reaction of Mg-2e^--Mg²⁺The forward direction is promoted, the reaction rate of the magnesium alloy coating is accelerated, the magnesium alloy can rapidly react in the coating containing phosphoric acid, and the reaction time is shortened.

Because the reaction is carried out in the forward direction, in the process of forming the film of the magnesium alloy, when the reaction film forming rate is higher than the corrosion rate of the magnesium alloy in the coating agent, the reaction is mainly film forming, so that the generation of film forming substances is quicker and more efficient, and the corrosion resistance is better.

Example 2

Different from the embodiment 1, the coating agent of the embodiment 2 consists of the following components in percentage by mass:

6% of phosphoric acid, 3.5% of calcium carbonate, 1.5% of barium nitrate, 2% of ammonium dihydrogen phosphate, 4.5% of manganese dihydrogen phosphate, 1% of EDTA-2Na and 81.5% of purified water.

Example 3

Different from the embodiment 1, the coating agent of the embodiment 3 consists of the following components in percentage by mass:

6.5% of phosphoric acid, 4% of calcium carbonate, 2% of barium nitrate, 2% of ammonium dihydrogen phosphate, 5% of manganese dihydrogen phosphate, 1% of EDTA-2Na and 79.5% of purified water.

Example 4

Different from the embodiment 1, the coating agent of the embodiment 4 consists of the following components in percentage by mass:

7% of phosphoric acid, 4.5% of calcium carbonate, 2.5% of barium nitrate, 2% of ammonium dihydrogen phosphate, 5.5% of manganese dihydrogen phosphate, 1% of EDTA-2Na and 77.5% of purified water.

Example 5

Different from the embodiment 1, the coating agent of the embodiment 5 consists of the following components in percentage by mass:

8% of phosphoric acid, 5% of calcium carbonate, 3% of barium nitrate, 2% of ammonium dihydrogen phosphate, 6% of manganese dihydrogen phosphate, 1% of EDTA-2Na and 75% of purified water.

Comparative example 1

Different from example 4, the coating agent of the magnesium alloy in the comparative example 1 consists of the following components in percentage by mass:

7% of phosphoric acid, 4.5% of calcium carbonate, 2.5% of barium nitrate, 2% of ammonium dihydrogen phosphate, 5.5% of manganese dihydrogen phosphate and 77.5% of purified water.

Comparative example 2

Different from example 4, the coating agent of the magnesium alloy in the comparative example 2 consists of the following components in percentage by mass:

7% of phosphoric acid, 4.5% of calcium carbonate, 2% of ammonium dihydrogen phosphate, 5.5% of manganese dihydrogen phosphate, EDTA-2Na 1% and 77.5% of purified water.

Performance testing

1. Salt spray resistance test of the magnesium alloy involucra:

working solutions prepared from the high-salt-spray-resistant magnesium alloy coating agents of the examples 1-5 and the comparative examples 1-2 are 10% (mass ratio) of the coating agent and 90% of pure water, and 2% of ammonium metavanadate is added. The magnesium alloy mobile phone middle plates with 65mm by 140mm which are subjected to the film formation reaction are uniformly degreased and regulated before the film formation. The magnesium alloy mobile phone middle plates of the tests were soaked in 1000ml of magnesium alloy coating working solution at room temperature of 30 ℃ for 1min, then washed with pure water for 30s, and baked at 120 ℃ for 10 min. And (3) cooling the treated magnesium alloy mobile phone middle plate for 1h to room temperature, and then putting the magnesium alloy mobile phone middle plate into a 5% NaCl solution neutral salt spray test box, wherein the temperature in the neutral salt spray test box is 35 ℃. And when the magnesium alloy mobile phone middle plate has corrosion oxidation points, ending the test and recording the salt spray resistance time.

2. And (3) detecting the appearance color of the magnesium alloy coating:

the appearance color of the coating of each test panel was visually observed, and 4 evaluations were performed, in which:

very good: off-white color

O: off-white color

And (delta): grey colour

X: and grey black.

3. Fineness of magnesium alloy coating film:

the fineness of the coating on the surface of each test plate was observed with an electron microscope, and 4 evaluations were performed, in which:

very good: excellent in fineness

O: has good fineness

And (delta): general degree of fineness

X: the fineness is slightly inferior.

4. The test results are shown in Table 1.

TABLE 1 test results of formation of magnesium alloy coating agent

From the above test results, it is clear that the magnesium alloy coating film in example 4 has the best salt spray resistance, pale appearance and fine fineness. Referring to example 4 and comparative example 1, in which EDTA-2Na was not added, the high salt spray resistance was significantly reduced and the appearance color and fineness were also reduced to various degrees because CaMg was contained in the film-forming substance₂(PO₄)₂The ratio of (a) to (b) is higher. Referring to example 4 and comparative example 2, the apparent color and fineness were significantly reduced due to Ca₃(PO₄)₂The film layer is thick, the color is gray, and the film layer is loose, porous and not fine enough.

5. And (3) resistance value testing:

the magnesium alloy part of this embodiment is the cell-phone medium plate, and this cell-phone medium plate plays the effect of fixed cell-phone antenna and main circuit board, and if the involucra is too thick then resistance value is big, and electric conductive property is poor, and cell-phone signal network can receive very big influence. According to the industrial standard, the resistance value between two opposite angles (the farthest distance) of the magnesium alloy middle plate is less than or equal to 1 omega, the magnesium alloy middle plate is qualified, the smaller the resistance value is, the better the conductivity is, and the better the mobile phone signal network is. The two diagonal test points of the mobile phone middle plate are AB respectively₁And A₁B, the resistance values of each example and each comparative example were separately tested using a DT9205A high precision multimeter, and the results are shown in table 2.

TABLE 2 resistance value test

From the above test results, the magnesium alloy coating formulation in example 4 has the smallest proportional resistance and the best conductivity. Reference example 4 and comparative exampleComparative example 1, in which EDTA-2Na was not added, the film-forming material contained CaMg, which is a higher resistance and poorer conductivity₂(PO₄)₂The ratio of (a) to (b) is higher. Referring to example 4 and comparative example 2, the resistance value was significantly increased due to Ca₃(PO₄)₂The film layer is thicker.

The above embodiments are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited thereby, and any insubstantial changes and substitutions made by those skilled in the art based on the present invention are within the protection scope of the present invention.