CN108930042A - A kind of preparation method of Mg alloy surface super-hydrophobic film - Google Patents

Abstract

A method for preparing a superhydrophobic film on the surface of a magnesium alloy disclosed by the present invention comprises the following steps: step 1, placing the pretreated magnesium alloy in an electrolyte solution of a silicate system, the magnesium alloy is used as an anode, and the stainless steel plate is used as a cathode , carry out micro-arc oxidation treatment, and form a micro-arc oxidation ceramic layer on the surface of the magnesium alloy; step 2, immerse the magnesium alloy treated in step 1 in an organic phosphoric acid solution for chemical etching, and obtain a magnesium alloy micro-arc oxidation sample; step 3 1. Clean the magnesium alloy micro-arc oxidation sample in step 2 with deionized water and soak it in ethanol stearic acid solution, then take out the sample and air-dry it naturally to form a super-hydrophobic film on the surface of the magnesium alloy. The magnesium alloy micro-arc oxidation pretreatment process is simple, the cycle is short, and the controllability is good. The micro-arc oxidation electrolyte used is alkaline, which is environmentally friendly and can be mass-produced.

Description

A kind of preparation method of superhydrophobic film on the surface of magnesium alloy

technical field

The invention belongs to the technical field of light metal surface modification methods, and relates to a preparation method of a superhydrophobic film on the surface of a magnesium alloy.

Background technique

Magnesium alloy has a series of unique advantages such as low density, high specific strength/stiffness, high damping, good thermal conductivity and electromagnetic shielding, and magnesium alloy products are easy to recycle and reuse, and have no pollution to the environment. It is called "21 "Century Green Engineering Materials" have been widely used in aerospace, national defense, automobile, 3C products and other fields. However, due to the high chemical activity of magnesium alloys, its standard electrode potential is very negative (-2.37V), which makes magnesium alloys extremely susceptible to corrosion damage, especially in non-alkaline solution media and humid environments containing ^Cl- , This greatly limits the wide application of magnesium alloys in many fields. Therefore, how to improve the corrosion resistance of magnesium alloys and expand their engineering applications has been attracting attention.

Magnesium alloys can be improved by various surface treatment methods to improve their corrosion resistance, including micro-arc oxidation, chemical conversion coating, metal coating, organic coating, and laser surface treatment. Among them, micro-arc oxidation is a new treatment process that has emerged in recent years to in-situ grow ceramic films mainly based on matrix metal oxides on the metal surface. It has a good effect on magnesium alloy anticorrosion and wear resistance. However, a large number of micropores and cracks on the surface of the micro-arc oxidation film make it easy for the corrosive medium to penetrate and corrode, thus affecting the service life of the protective layer under severe working conditions. However, the micro-rough porous structure on the surface of the micro-arc oxidation layer provides favorable conditions for the further preparation of a corrosion-resistant, anti-fouling, self-cleaning super-hydrophobic film layer on its surface.

At present, the method for preparing a super-hydrophobic film on the surface of a magnesium alloy combined with a micro-arc oxidation process includes: after preparing a micro-arc oxidation film, etching with acrylic acid, and then spin-coating vinyl polydimethylsiloxane to prepare a super-hydrophobic film. Surface: After micro-arc oxidation, it is modified with fluorosilane and cured to obtain a super-hydrophobic film layer. However, the etchant acrylic acid used in the above method has moderate toxicity and was listed as a carcinogen in the list of carcinogens published by the International Agency for Research on Cancer of the World Health Organization in 2017. Although the fluorosilane used in the modifier has a good superhydrophobic effect, its price is high, and fluoride ions are harmful to the human body and the environment.

Contents of the invention

The purpose of the invention is to provide a method for preparing a superhydrophobic film on the surface of a magnesium alloy, which can effectively improve the corrosion resistance of the magnesium alloy.

The technical scheme adopted in the present invention is, a kind of preparation method of superhydrophobic film on the surface of magnesium alloy, comprises the following steps:

Step 1, placing the pretreated magnesium alloy in the electrolyte of the silicate system, the magnesium alloy is used as the anode, and the stainless steel plate is used as the cathode, and micro-arc oxidation treatment is performed to form a micro-arc oxidation ceramic layer on the surface of the magnesium alloy;

Step 2, immersing the magnesium alloy treated in step 1 in an organic phosphoric acid solution for chemical etching to obtain a magnesium alloy micro-arc oxidation sample;

Step 3. Clean the magnesium alloy micro-arc oxidation sample in step 2 with deionized water, soak it in stearic acid ethanol solution, then take out the sample and air-dry it naturally to form a super-hydrophobic film on the surface of the magnesium alloy.

The present invention is also characterized in that,

The pretreatment process of the magnesium alloy in step 1 is as follows: after degreasing the magnesium alloy substrate, use 240#, 600#, 1000# SiC sandpaper to polish its surface and edges until smooth, then clean and dry.

In step 1: the total content of solutes in the electrolyte of the silicate system is 15-21 g/L, wherein the content of sodium silicate is 9-11 g/L, and the content of sodium hydroxide is 6-10 g/L.

The electrical parameters of the micro-arc oxidation in step 1 are as follows: the current density is 10A/dm ² , the frequency is 500 Hz, the duty ratio is 10%, and the micro-arc oxidation time is 5-10 min.

During the chemical etching process in step 2: the content of the organic phosphoric acid solution is 30-50 g/L, the etching time is 2 min, and the etching temperature is 40±2°C.

In step 3, the concentration of stearic acid ethanol solution is 0.01ml/L, the soaking time is 1.5-2.5h, and the soaking temperature is 60±2°C.

The beneficial effects of the present invention are:

(1) The preparation method of the super-hydrophobic film on the surface of magnesium alloy of the present invention has simple micro-arc oxidation pretreatment process, short cycle and good controllability, and the micro-arc oxidation electrolyte used is alkaline, environmentally friendly and reproducible mass production;

(2) The preparation method of the superhydrophobic film on the surface of the magnesium alloy of the present invention, the organic phosphoric acid solution used in the chemical etching after the micro-arc oxidation of the magnesium alloy and the stearic acid ethanol solution used for modification are low in cost, harmless to the human body, environmentally friendly and pollution-free, It is an environmentally friendly formula;

(3) The preparation method of the superhydrophobic film on the surface of the magnesium alloy of the present invention, the quality of the superhydrophobic film layer of the magnesium alloy is good, and it shows excellent superhydrophobicity, that is, the contact angle to water is greater than 150 °, and the neutral salt spray test test 168h , without any change on the surface, which can effectively improve the corrosion resistance of magnesium alloys;

(4) The preparation method of the superhydrophobic film on the surface of the magnesium alloy of the present invention has simple preparation process, short preparation period, good controllability, high efficiency and low cost, is applicable to magnesium alloys of different grades, and can realize industrialized mass production.

Description of drawings

Fig. 1 is the SEM figure of the magnesium alloy surface after the micro-arc oxidation treatment of the preparation method of a kind of magnesium alloy surface superhydrophobic film of the present invention;

Fig. 2 is the contact angle figure of the magnesium alloy surface after the micro-arc oxidation treatment of the preparation method of a kind of magnesium alloy surface superhydrophobic film of the present invention;

Fig. 3 is the SEM figure of the magnesium alloy surface hydrophobic film layer prepared without etching of the preparation method of a kind of magnesium alloy surface superhydrophobic film of the present invention;

Fig. 4 is the contact angle figure of the magnesium alloy surface hydrophobic film layer that the preparation method of a kind of magnesium alloy surface superhydrophobic film of the present invention is not etched;

Fig. 5 is the SEM picture of the magnesium alloy surface superhydrophobic film layer that the preparation method of a kind of magnesium alloy surface superhydrophobic film of the present invention prepares;

Fig. 6 is the contact angle figure of the AZ91D magnesium alloy surface superhydrophobic film layer prepared by a kind of preparation method of magnesium alloy surface superhydrophobic film of the present invention;

Fig. 7 is the contact angle figure of the MB8 magnesium alloy surface superhydrophobic film layer that the preparation method of a kind of magnesium alloy surface superhydrophobic film of the present invention prepares;

8 is a contact angle diagram of a superhydrophobic film layer on the surface of a ZM51M magnesium alloy prepared by a method for preparing a superhydrophobic film on the surface of a magnesium alloy according to the present invention.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

A kind of preparation method of magnesium alloy surface superhydrophobic film of the present invention comprises the following steps:

Step 1. After degreasing the magnesium alloy substrate, polish its surface and edges with 240#, 600#, and 1000# SiC sandpaper in sequence until it is flat and then clean and dry; then place the treated magnesium alloy in silicate In the electrolyte of the system, the magnesium alloy is used as the anode, and the stainless steel plate is used as the cathode, and the micro-arc oxidation treatment is performed to form a micro-arc oxidation ceramic layer on the surface of the magnesium alloy;

The total content of solute in the electrolyte of the silicate system is 15-21g/L, of which, the content of sodium silicate is 9-11g/L, and the content of sodium hydroxide is 6-10g/L;

The electrical parameters of the micro-arc oxidation are: constant current mode, the current density is 10A/dm ² , the frequency is 500Hz, the duty ratio is 10%, and the micro-arc oxidation time is 5-10min.

Step 2, immersing the magnesium alloy treated in step 1 in an organic phosphoric acid solution with a content of 30 to 50 g/L for chemical etching for 2 minutes at an etching temperature of 40±2° C. to obtain a magnesium alloy micro-arc oxidation sample;

Step 3. First, wash the magnesium alloy micro-arc oxidation sample in step 2 with deionized water, and then soak it in stearic acid ethanol solution with a concentration of 0.01ml/L for 1.5-2.5h. The soaking temperature is 60±2°C. Then the sample was taken out and air-dried naturally to form a super-hydrophobic film on the surface of the magnesium alloy.

The micro-arc oxidation electrolyte of the silicate system used in the present invention can adjust the pH value to ensure that the ceramic layer is not corroded, and maintain proper conductivity so that the partial pressure of the circuit is mainly applied to the processed sample. It can be seen from Figure 1 that the surface of magnesium alloys after micro-arc oxidation is uneven, and there are many pore-like structures and island-like structures of different sizes formed after spark discharge, which are similar to volcanic structures and are typical micro-arc oxidation surface morphology. , has a certain roughness, and the surface of the magnesium alloy is in a super-hydrophilic state after micro-arc oxidation. Figure 2 shows the contact angle diagram of the magnesium alloy surface after micro-arc oxidation, and the contact angle is only 6°.

There are generally two ways to construct hydrophobic surfaces: one is to modify low surface energy substances on micro-nano rough surfaces, and the other is to construct micro-nano rough structures on low surface energy substances. After micro-arc oxidation of magnesium alloy, a porous ceramic layer with a certain roughness is formed. If the second method is used to directly modify the low surface energy substances on the micro-nano rough surface, the result is shown in Figure 3. The surface of the magnesium alloy prepared without etching The SEM image of the hydrophobic film layer shows that the pores on the surface of the film layer are partially closed or semi-closed, and there are papillae structures between the pores, indicating that the surface morphology and surface structure can be changed after modification with low surface energy substances, but the surface still exists. The porous structure features after micro-arc oxidation, the surface energy is high, and water is easily absorbed and infiltrated into the pores so that it is difficult to reach a super-hydrophobic state. The maximum contact angle is only 137°, which is a hydrophobic state.

On this basis, chemical etching is added, and the porous ceramic layer formed after micro-arc oxidation is etched with safe and non-toxic organic phosphoric acid. During the etching process, a chemical reaction occurs to obtain organic magnesium phosphate to properly fill the pores of the ceramic layer and increase the roughness. , to obtain a micronano rough surface. However, if the concentration of etchant, etching temperature and time are not selected properly, most of the micro-arc oxidation porous structure will be retained or the micro-arc oxidation film will be corroded excessively.

Stearic acid is a substance with low surface energy. It modifies the micro-nano rough surface of magnesium alloy, and the long chain of hydrocarbon group with hydrophobic effect is grafted to the rough surface of magnesium alloy, so that the surface contact angle increases significantly and reaches a super-hydrophobic state. . The parameters of the stearic acid ethanol solution of the present invention are the optimal ranges obtained after multiple test comparisons. If the concentration is too low, the modification time is too short or the temperature is too low, the surface self-assembly is insufficient, that is, the long-chain hydrocarbon group with hydrophobic effect Only a small part is grafted to the rough magnesium alloy surface; if the concentration is too high, the modification time is too long or the temperature is too high, the surface reaction will be excessive and a large number of cracks will appear, so that the superhydrophobic state cannot be achieved.

The preparation method of the superhydrophobic film on the surface of magnesium alloy of the present invention has the advantages of simple micro-arc oxidation pretreatment process of magnesium alloy, short cycle and good controllability, and the micro-arc oxidation electrolyte used is alkaline, which is environmentally friendly and can be mass-produced; The preparation method of the superhydrophobic film on the surface of the magnesium alloy of the present invention, the organic phosphoric acid solution used in the chemical etching after the micro-arc oxidation of the magnesium alloy and the stearic acid ethanol solution used in the modification are low in cost, harmless to the human body, environmentally friendly and pollution-free, and belong to the environment-friendly type. Formula; the preparation method of the superhydrophobic film on the surface of the magnesium alloy of the present invention, the quality of the superhydrophobic film layer of the magnesium alloy is good, showing excellent superhydrophobicity, that is, the contact angle to water is greater than 150°, and the neutral salt spray test is tested for 168h, There is no change on the surface, which can effectively improve the corrosion resistance of the magnesium alloy; the preparation method of the superhydrophobic film on the surface of the magnesium alloy of the present invention has simple preparation process, short preparation cycle, good controllability, high efficiency and low cost, and is suitable for different grades The magnesium alloy can realize industrial mass production.

Example 1

Step 1. After degreasing the AZ91D magnesium alloy substrate, polish its surface and edges with 240#, 600#, and 1000# SiC sandpaper in sequence until it is flat and then clean and dry; then place the treated magnesium alloy in silicic acid In the electrolyte of the salt system, the magnesium alloy is used as the anode, and the stainless steel plate is used as the cathode, and the micro-arc oxidation treatment is performed to form a micro-arc oxidation ceramic layer on the surface of the magnesium alloy;

In the electrolyte of the silicate system, the total solute content is 15g/L, the sodium silicate content is 9g/L, and the sodium hydroxide content is 6g/L;

The electrical parameters of the micro-arc oxidation are: constant current mode, the current density is 10A/dm ² , the frequency is 500Hz, the duty cycle is 10%, and the micro-arc oxidation time is 10min.

Step 2, immersing the magnesium alloy treated in step 1 in an organic phosphoric acid solution with a content of 50 g/L for chemical etching for 2 minutes at an etching temperature of 40° C. to obtain a magnesium alloy micro-arc oxidation sample;

Step 3. First, wash the magnesium alloy micro-arc oxidation sample in step 2 with deionized water, and then soak it in a stearic acid ethanol solution with a concentration of 0.01ml/L for 2.5 hours. The soaking temperature is 60°C, and then place the sample Take it out, let it dry naturally, and form a super-hydrophobic film layer on the surface of the magnesium alloy.

Figure 5 is the surface topography of the prepared magnesium alloy superhydrophobic film layer. It can be seen from the figure that the surface of the magnesium alloy modified by stearic acid, the pores of the ceramic layer are basically completely closed, and the surface features after micro-arc oxidation basically disappear. , and many protrusions of different sizes appear, forming a large number of micro-nano composite structures on the surface of the magnesium alloy, and obtaining a superhydrophobic state on the surface of the magnesium alloy. This embodiment is to prepare a super-hydrophobic film on the surface of an AZ91D magnesium alloy with a film thickness of 40 μm. As shown in Figure 6, it is a contact angle diagram of the super-hydrophobic film on the surface of the prepared magnesium alloy. The contact angle is 152°, showing It is super-hydrophobic; the sample was tested in the neutral salt spray test for 186 hours, and there was no corrosion on the surface, showing good corrosion resistance.

Example 2

Step 1. After degreasing the MB8 magnesium alloy substrate, polish its surface and edges with 240#, 600#, and 1000# SiC sandpaper in sequence until it is flat and then clean and dry; then place the treated magnesium alloy in silicic acid In the electrolyte of the salt system, the magnesium alloy is used as the anode, and the stainless steel plate is used as the cathode, and the micro-arc oxidation treatment is performed to form a micro-arc oxidation ceramic layer on the surface of the magnesium alloy;

In the electrolyte system of the silicate system, the total content of solute is 18g/L, the content of sodium silicate is 10g/L, and the content of sodium hydroxide is 8g/L;

The electrical parameters of the micro-arc oxidation are: constant current mode, the current density is 10A/dm ² , the frequency is 500Hz, the duty ratio is 10%, and the micro-arc oxidation time is 8min.

Step 2, immersing the magnesium alloy treated in step 1 in an organic phosphoric acid solution with a content of 40 g/L for chemical etching for 2 minutes at an etching temperature of 41° C. to obtain a magnesium alloy micro-arc oxidation sample;

Step 3. First, wash the magnesium alloy micro-arc oxidation sample in step 2 with deionized water and soak it in ethanol stearic acid solution with a concentration of 0.01ml/L for 2 hours. The soaking temperature is 61°C, and then take out the sample , naturally air-dried to form a super-hydrophobic film layer on the surface of the magnesium alloy.

In this embodiment, a superhydrophobic film is prepared on the surface of an MB8 magnesium alloy with a film thickness of 30 μm. As shown in Figure 7, its contact angle is 154°, showing superhydrophobic performance; the sample is tested in a neutral salt spray test After 186 hours, no corrosion appeared on the surface, showing good corrosion resistance.

Example 3

Step 1. After degreasing the ZM51M magnesium alloy substrate, polish its surface and edges with 240#, 600#, and 1000# SiC sandpaper in sequence until it is flat and then clean and dry; then place the treated magnesium alloy in silicic acid In the electrolyte of the salt system, the magnesium alloy is used as the anode, and the stainless steel plate is used as the cathode, and the micro-arc oxidation treatment is performed to form a micro-arc oxidation ceramic layer on the surface of the magnesium alloy;

In the electrolyte system of the silicate system, the total content of solute is 21g/L, the content of sodium silicate is 11g/L, and the content of sodium hydroxide is 10g/L;

The electrical parameters of the micro-arc oxidation are: constant current mode, the current density is 10A/dm ² , the frequency is 500Hz, the duty cycle is 10%, and the micro-arc oxidation time is 5min.

Step 2, immersing the magnesium alloy treated in step 1 in an organic phosphoric acid solution with a content of 30 g/L for chemical etching for 2 minutes at an etching temperature of 42° C. to obtain a magnesium alloy micro-arc oxidation sample;

Step 3. First, wash the magnesium alloy micro-arc oxidation sample in step 2 with deionized water and soak it in ethanol stearic acid solution with a concentration of 0.01ml/L for 1.5h. The soaking temperature is 62°C, and then place the sample Take it out, let it dry naturally, and form a super-hydrophobic film layer on the surface of the magnesium alloy.

In this embodiment, a superhydrophobic film is prepared on the surface of a ZM51M magnesium alloy with a film thickness of 20 μm. As shown in Figure 8, its contact angle is 151°, showing superhydrophobic performance; the sample is tested in a neutral salt spray test After 186 hours, no corrosion appeared on the surface, showing good corrosion resistance.

Example 4

Step 1. After degreasing the AZ31B magnesium alloy substrate, polish its surface and edges with 240#, 600#, and 1000# SiC sandpaper in turn until it is flat and then clean and dry; then place the treated magnesium alloy in silicic acid In the electrolyte of the salt system, the magnesium alloy is used as the anode, and the stainless steel plate is used as the cathode, and the micro-arc oxidation treatment is performed to form a micro-arc oxidation ceramic layer on the surface of the magnesium alloy;

In the electrolyte system of the silicate system, the total content of solute is 16g/L, the content of sodium silicate is 10g/L, and the content of sodium hydroxide is 6g/L;

The electrical parameters of the micro-arc oxidation are: constant current mode, the current density is 10A/dm ² , the frequency is 500Hz, the duty cycle is 10%, and the micro-arc oxidation time is 7min.

Step 2, immersing the magnesium alloy treated in step 1 in an organic phosphoric acid solution with a content of 35 g/L for chemical etching for 2 minutes at an etching temperature of 38° C. to obtain a magnesium alloy micro-arc oxidation sample;

Step 3. First, wash the magnesium alloy micro-arc oxidation sample in step 2 with deionized water and soak it in ethanol stearic acid solution with a concentration of 0.01ml/L for 2 hours. The soaking temperature is 59°C, and then take out the sample , naturally air-dried to form a super-hydrophobic film layer on the surface of the magnesium alloy.

Example 5

Step 1. After degreasing the ZK60A magnesium alloy substrate, polish its surface and edges with 240#, 600#, and 1000# SiC sandpaper in turn until it is flat and then clean and dry; then place the treated magnesium alloy in silicic acid In the electrolyte of the salt system, the magnesium alloy is used as the anode, and the stainless steel plate is used as the cathode, and the micro-arc oxidation treatment is performed to form a micro-arc oxidation ceramic layer on the surface of the magnesium alloy;

In the electrolyte system of the silicate system, the total content of solute is 19g/L, the content of sodium silicate is 9g/L, and the content of sodium hydroxide is 10g/L;

The electrical parameters of the micro-arc oxidation are: constant current mode, the current density is 10A/dm ² , the frequency is 500Hz, the duty cycle is 10%, and the micro-arc oxidation time is 9min.

Step 2, immersing the magnesium alloy treated in step 1 in an organic phosphoric acid solution with a content of 45 g/L for chemical etching for 2 minutes at an etching temperature of 39° C. to obtain a magnesium alloy micro-arc oxidation sample;

Step 3. First, wash the magnesium alloy micro-arc oxidation sample in step 2 with deionized water and soak it in ethanol stearic acid solution with a concentration of 0.01ml/L for 1.5h at a temperature of 60°C, and then place the sample Take it out, let it dry naturally, and form a super-hydrophobic film layer on the surface of the magnesium alloy.

Claims (6)

1. a kind of preparation method of Mg alloy surface super-hydrophobic film, which comprises the following steps:

Pretreated magnesium alloy is placed in the electrolyte of silicate systems by step 1, and magnesium alloy is as anode, stainless steel plate As cathode, micro-arc oxidation treatment is carried out, forms micro-arc oxidation ceramic layer in Mg alloy surface；

Step 1 treated magnesium alloy is immersed in organic phosphoric acid solution and carries out chemical etching by step 2, obtains magnesium alloy differential arc Oxidised samples；

Magnesium alloy differential arc oxidation sample in step 2 first is cleaned to be placed in stearic acid ethanol solution and be soaked by step 3 with deionized water Bubble, then sample is taken out, natural air drying, form super-hydrophobic film layer in Mg alloy surface.

2. a kind of preparation method of Mg alloy surface super-hydrophobic film as described in claim 1, which is characterized in that institute in step 1 State the preprocessing process of magnesium alloy are as follows: after deoiling to magnesium alloy substrate, successively use the SiC sand paper of 240#, 600#, 1000# Its surface and edge are carried out to be polishing to smooth rear cleaning-drying.

3. a kind of preparation method of Mg alloy surface super-hydrophobic film as described in claim 1, which is characterized in that in step 1: institute Stating solute total content in the electrolyte of silicate systems is 15~21g/L, wherein silicic acid sodium content is 9~11g/L, hydroxide Sodium content is 6~10g/L.

4. a kind of preparation method of Mg alloy surface super-hydrophobic film as described in claim 1, which is characterized in that institute in step 1 The differential arc oxidation electrical parameter stated are as follows: current density 10A/dm², frequency 500Hz, duty ratio 10%, the differential arc oxidation time For 5~10min.

5. a kind of preparation method of Mg alloy surface super-hydrophobic film as described in claim 1, which is characterized in that described in step 2 Chemical etching during: organic phosphoric acid solution content be 30~50g/L, etch period 2min, etching temperature be 40 ± 2 ℃。

6. a kind of preparation method of Mg alloy surface super-hydrophobic film as described in claim 1, which is characterized in that in step 3, firmly The concentration of resin acid ethanol solution is 0.01ml/L, and soaking time is 1.5~2.5h, and soaking temperature is 60 ± 2 DEG C.