CN113862751A

CN113862751A - Preparation method of self-hole-sealing micro-arc oxidation film on surface of magnesium alloy

Info

Publication number: CN113862751A
Application number: CN202111124723.9A
Authority: CN
Inventors: 尚伟; 马宸; 张志远; 温玉清; 彭宁
Original assignee: Guilin University of Technology
Current assignee: Guilin University of Technology
Priority date: 2021-09-25
Filing date: 2021-09-25
Publication date: 2021-12-31

Abstract

The invention discloses a preparation method of a magnesium alloy surface self-sealing micro-arc oxidation film. Firstly, the AZ91 magnesium alloy is polished, washed by water, alkali, water and ultrasonically cleaned. And then preparing a micro-arc oxidation electrolyte, putting the AZ91 magnesium alloy into the micro-arc oxidation electrolyte as an anode to perform micro-arc oxidation treatment, taking a stainless steel as a cathode, adopting a four-time boosting oxidation mode, and dropwise adding titanium dioxide sol into the micro-arc oxidation electrolyte in the boosting process. And finally, taking the AZ91 magnesium alloy out, and drying at 50 ℃ to obtain the self-hole-sealing micro-arc oxidation film on the surface of the magnesium alloy. The method adopts one-step in-situ preparation of the non-porous micro-arc oxidation film, realizes self-sealing during micro-arc oxidation, and the prepared magnesium alloy surface micro-arc oxidation film has a non-porous structure, is smooth in surface, has no microcrack, and can improve the corrosion resistance of the magnesium alloy.

Description

Preparation method of self-hole-sealing micro-arc oxidation film on surface of magnesium alloy

Technical Field

The invention belongs to the field of magnesium alloy surface treatment, and particularly relates to a preparation method of a self-sealing hole micro-arc oxidation film on a magnesium alloy surface.

Background

The magnesium alloy is a high-performance light structural material taking magnesium as a raw material, has the specific gravity similar to that of plastic, has the rigidity and the strength not inferior to that of aluminum, has the excellent performances of stronger earthquake resistance, electromagnetic resistance, heat conduction, electric conduction and the like, can be completely recycled without pollution, is inferior to iron and aluminum in metal reserves on the earth, is more and more emphasized by people, and is known as a green engineering material in the 21 st century. Nowadays, the traditional metal materials are increasingly exhausted, the magnesium alloy has wide application prospects in the industries of automobiles, aerospace, medicine and electronics, but the application of the magnesium alloy is limited due to poor corrosion resistance. The protective coating is an effective method for improving the corrosion resistance, and the micro-arc oxidation film has the most development prospect due to the advantages of low cost, easy preparation, high corrosion resistance, high wear resistance and the like. Micro-arc oxidation is a surface treatment technology which can greatly improve the corrosion resistance and the wear resistance of magnesium alloy and is currently applied to the surface treatment of aluminum, magnesium and titanium alloy. However, the ceramic film obtained by the traditional micro-arc oxidation has a plurality of micropores, and corrosive media easily penetrate through the film along the micropores and enter the matrix, so that the corrosion resistance of the film is reduced. The self-hole-sealing micro-arc oxidation film is prepared in situ on the surface of the magnesium alloy by adopting the electrolyte of a phosphate system, so that the active and passive protection capability is provided for the magnesium alloy matrix, and the occurrence of a corrosion process is inhibited.

Disclosure of Invention

The invention aims to provide a preparation method of a magnesium alloy surface self-hole-sealing micro-arc oxidation film, which is used for magnesium alloy surface treatment to obtain a micro-arc oxidation film layer without pores and with high corrosion resistance.

The method comprises the following specific steps:

(1) polishing and washing AZ91 magnesium alloy by 180#, 600#, 1200# and 1500# waterproof abrasive paper step by step, then removing oil in alkaline degreasing liquid at 50-70 ℃ for 1-5 minutes, respectively washing the surface of AZ91 magnesium alloy by hot water and cold water, then ultrasonically washing in absolute ethyl alcohol for 10-15 minutes, washing the surface by distilled water after washing, then ultrasonically washing in distilled water for 5-10 minutes, and drying for later use. The alkaline degreasing fluid comprises the following components in percentage by weight: 15-20 g/L of sodium phosphate, 15-20 g/L of sodium hydroxide and 30-40 g/L of sodium carbonate.

(2) And (2) placing the AZ91 magnesium alloy treated in the step (1) into a micro-arc oxidation electrolyte as an anode for micro-arc oxidation treatment, wherein the cathode is stainless steel, a pulse micro-arc oxidation mode is adopted, the pulse frequency is 50-200 Hz, and the duty ratio is 30-70%. The boosting mode is as follows: firstly, boosting to 150V at the speed of 10 volts/min, and then boosting to 220V at the speed of 5 volts/min; then the temperature is reduced to 180V, and the temperature is increased to 240V at the speed of 10V/min; then, the temperature is reduced to 200V and increased to 260V at the speed of 10V/min; then, the voltage is decreased to 220V and then increased to 280V at a speed of 10V/min. In each boosting process, titanium dioxide sol is dripped into the electrolyte, and the electrolyte needs to be stirred magnetically and cooled by a cold water bath in the whole experiment process. And after the micro-arc oxidation is finished, washing the AZ91 magnesium alloy by using distilled water, and drying in a forced air drying oven at 50 ℃ to obtain the self-hole-sealing micro-arc oxidation film on the surface of the magnesium alloy. The micro-arc oxidation electrolyte comprises the following components in percentage by weight: 5-10 g/L of sodium phosphate, 8-12 g/L of potassium hydroxide, 5-10 g/L of sodium fluoride, 4-6 g/L of sodium tetraborate, 1-5 g/L of sodium tungstate, 3-5 ml/L of triethanolamine, 3-5 ml/L of glycerol and 5-10 g/L of potassium fluorozirconate.

The sodium phosphate, sodium carbonate, sodium hydroxide, sodium fluoride, potassium hydroxide, sodium tetraborate, sodium tungstate, triethanolamine, glycerol, potassium fluorozirconate, titanium dioxide and absolute ethyl alcohol are all chemically pure or above.

The method adopts one-step in-situ preparation of the non-porous micro-arc oxidation film, realizes self-sealing during micro-arc oxidation, and the prepared magnesium alloy surface micro-arc oxidation film has a non-porous structure, is smooth in surface, has no microcrack, and can improve the corrosion resistance of the magnesium alloy.

Drawings

FIG. 1 is an SEM image of the self-sealing micro-arc oxide film (a, c) on the surface of the magnesium alloy prepared by the embodiment of the present invention and the micro-arc oxide film (b, d) on the surface of the magnesium alloy prepared by the conventional method.

FIG. 2 is a polarization curve of a self-hole-sealing micro-arc oxide film on the surface of a magnesium alloy prepared according to the embodiment of the present invention and a micro-arc oxide film on the surface of a magnesium alloy prepared by a conventional method.

FIG. 3 is an electrochemical impedance spectrum of a self-sealing micro-arc oxide film on the surface of a magnesium alloy prepared according to an embodiment of the present invention and a micro-arc oxide film on the surface of a magnesium alloy prepared by a conventional method.

Detailed Description

Example (b):

(1) the AZ91 magnesium alloy is gradually polished and washed by 180#, 600#, 1200# and 1500# waterproof abrasive paper, and then oil is removed in alkaline degreasing fluid, wherein the alkaline degreasing fluid comprises the following formula: 20g/L of sodium phosphate, 20g/L of sodium hydroxide and 30g/L of sodium carbonate, wherein the oil removing temperature is 70 ℃, the surface of the AZ91 magnesium alloy is respectively cleaned by hot water and cold water after oil removing is carried out for 1 minute, then the surface is cleaned by ultrasonic waves in absolute ethyl alcohol for 10 minutes, the surface is cleaned by distilled water after the cleaning is finished, then the surface is cleaned by ultrasonic waves in distilled water for 10 minutes, and the mixture is dried for later use.

(2) And (2) placing the AZ91 magnesium alloy treated in the step (1) into a micro-arc oxidation electrolyte as an anode for micro-arc oxidation treatment, wherein the cathode is stainless steel, a pulse micro-arc oxidation mode is adopted, the pulse frequency is 50Hz, and the duty ratio is 30%. The boosting mode is as follows: firstly, boosting to 150V at the speed of 10 volts/min, and then boosting to 220V at the speed of 5 volts/min; then the temperature is reduced to 180V, and the temperature is increased to 240V at the speed of 10V/min; then, the temperature is reduced to 200V and increased to 260V at the speed of 10V/min; then, the voltage is decreased to 220V and then increased to 280V at a speed of 10V/min. In each boosting process, titanium dioxide sol is dripped into the electrolyte, and the electrolyte needs to be stirred magnetically and cooled by a cold water bath in the whole experiment process. And after the micro-arc oxidation is finished, washing the AZ91 magnesium alloy by using distilled water, and drying in a forced air drying oven at 50 ℃ to obtain the self-hole-sealing micro-arc oxidation film on the surface of the magnesium alloy. The micro-arc oxidation electrolyte comprises the following components in percentage by weight: 5g/L of sodium phosphate, 10g/L of potassium hydroxide, 10g/L of sodium fluoride, 4g/L of sodium tetraborate, 1g/L of sodium tungstate, 4ml/L of triethanolamine, 5ml/L of glycerol and 10g/L of potassium fluorozirconate.

The traditional preparation method of the micro-arc oxidation film comprises the following steps: at room temperature, placing the treated magnesium alloy obtained in the step (1) as an anode and a stainless steel sheet as a cathode in a micro-arc oxidation solution to perform micro-arc oxidation treatment by using pulse voltage to obtain a micro-arc oxidation film on the surface of the magnesium alloy; the electrical parameters were set as: the frequency is 50Hz, the duty ratio is 30 percent, the termination voltage is 220V, and the micro-arc oxidation time is 30 min; the micro-arc oxidation solution comprises the following components: 5g/L of sodium phosphate, 10g/L of sodium fluoride and 10g/L of potassium hydroxide.

The thickness of the film layer of the self-hole-sealing micro-arc oxidation film on the surface of the magnesium alloy prepared by the embodiment reaches more than 50 microns, and SEM representation shows that the surface of the film layer is flat and has no micropores or microcracks. The polarization curve and the alternating current impedance are one of the common electrochemical means in the corrosion science, and are effective tools for researching the corrosion rate of the metal surface film layer. The magnesium alloy surface self-sealing hole micro-arc oxidation film prepared in the embodiment is subjected to electrochemical corrosion resistance test, a three-electrode system (a magnesium alloy surface self-sealing hole micro-arc oxidation film sample is a research electrode, a platinum electrode is an auxiliary electrode, a saturated calomel electrode is a reference electrode) is adopted, and a NaCl solution with the mass percentage concentration of 3.5% is used as an electrolyte. The corrosion current density of the self-hole-sealing micro-arc oxidation film on the surface of the magnesium alloy obtained in the embodiment is 6.152 multiplied by 10^-7A/cm²The corrosion current density of the micro-arc oxidation film on the surface of the magnesium alloy prepared by the traditional method is 3.373 multiplied by 10^-5A/cm²And is reduced by two orders of magnitude. The electrochemical resistance of the magnesium alloy surface self-hole-sealing micro-arc oxidation film obtained by the embodiment reaches 5 th order of magnitude of 10, is larger than that of the magnesium alloy surface micro-arc oxidation film prepared by the traditional method, and shows obvious corrosion resistance.

Claims

1. A preparation method of a magnesium alloy surface self-sealing hole micro-arc oxidation film is characterized by comprising the following specific steps:

(1) polishing and washing AZ91 magnesium alloy by 180#, 600#, 1200# and 1500# waterproof abrasive paper step by step, then removing oil in alkaline degreasing liquid at 50-70 ℃ for 1-5 minutes, respectively washing the surface of AZ91 magnesium alloy by hot water and cold water, then ultrasonically washing in absolute ethyl alcohol for 10-15 minutes, washing the surface by distilled water after washing, then ultrasonically washing in distilled water for 5-10 minutes, and drying for later use; the alkaline degreasing fluid comprises the following components in percentage by weight: 15-20 g/L of sodium phosphate, 15-20 g/L of sodium hydroxide and 30-40 g/L of sodium carbonate;

(2) placing the AZ91 magnesium alloy treated in the step (1) into a micro-arc oxidation electrolyte as an anode for micro-arc oxidation treatment, wherein the cathode is made of stainless steel, a pulse micro-arc oxidation mode is adopted, the pulse frequency is 50-200 Hz, and the duty ratio is 30-70%; the boosting mode is as follows: firstly, boosting to 150V at the speed of 10 volts/min, and then boosting to 220V at the speed of 5 volts/min; then the temperature is reduced to 180V, and the temperature is increased to 240V at the speed of 10V/min; then, the temperature is reduced to 200V and increased to 260V at the speed of 10V/min; then the temperature is reduced to 220V, and then the temperature is increased to 280V at the speed of 10V/min; in each boosting process, titanium dioxide sol is dropwise added into the electrolyte, and the electrolyte needs to be subjected to magnetic stirring and cold water bath cooling in the whole experiment process; after micro-arc oxidation is finished, washing the AZ91 magnesium alloy by using distilled water, and drying the magnesium alloy in a forced air drying oven at 50 ℃ to obtain a self-hole-sealing micro-arc oxidation film on the surface of the magnesium alloy; the micro-arc oxidation electrolyte comprises the following components in percentage by weight: 5-10 g/L of sodium phosphate, 8-12 g/L of potassium hydroxide, 5-10 g/L of sodium fluoride, 4-6 g/L of sodium tetraborate, 1-5 g/L of sodium tungstate, 3-5 ml/L of triethanolamine, 3-5 ml/L of glycerol and 5-10 g/L of potassium fluorozirconate.

2. The method of claim 1, wherein the sodium phosphate, sodium carbonate, sodium hydroxide, sodium fluoride, potassium hydroxide, sodium tetraborate, sodium tungstate, triethanolamine, glycerol, potassium fluorozirconate, titanium dioxide, and anhydrous ethanol are chemically pure or purer.