CN111826606A - A kind of surface plasma oxidation method of aluminum and aluminum alloy - Google Patents

Abstract

The invention belongs to the technical field of surface modification of metal materials, and particularly relates to a method for plasma oxidation of aluminum and aluminum alloy surfaces. It is completed by arc enhanced glow discharge (AEGD) technology. The electron flow is generated by arc discharge, and then the electrons collide with oxygen and other gases to ionize them to generate oxygen plasma, and a positive bias electric field is applied to the surface of the substrate to generate glow discharge. The negatively charged oxygen ions are attracted to the surface of the substrate for oxidation reaction, thereby forming an aluminum oxide protective film layer. Compared with the traditional micro-arc oxidation and anodic oxidation technology, the method has the advantages of no environmental pollution, etc., and can effectively improve the pitting corrosion resistance of the aluminum alloy surface.

Description

A kind of surface plasma oxidation method of aluminum and aluminum alloy

Technical field:

The invention belongs to the technical field of surface modification of metal materials, and particularly relates to a method for plasma oxidation of aluminum and aluminum alloy surfaces.

Background technique:

Aluminum and aluminum alloy materials have a series of advantages such as low relative density, high specific strength, good plasticity, excellent electrical and thermal conductivity, easy processing and forming, and low price. They are widely used in aerospace, shipbuilding, weapon industry and light industry building materials. It is one of the key materials with economic value and commercial application significance. In particular, aluminum alloy materials can combine with oxygen in the air to form a thin oxide film on the surface of the alloy. However, this kind of oxide film is relatively thin, generally only 2nm and has a porous structure. Under the conditions of seawater or marine environment, chloride ions easily penetrate the oxide film and cause pitting corrosion, which is often difficult to meet the requirements. Therefore, it is often necessary to treat the surface of the alloy by electrochemical means to form a uniform, continuous and dense porous alumina film on the surface of the aluminum alloy, so as to improve the corrosion resistance and wear resistance of the material surface.

Although some surface treatment methods (such as: anodizing, chemical oxidation, micro-arc oxidation, etc.) are widely used, the oxide films prepared by these technologies have many defects and cause great environmental pollution. With the development of society, the requirements for the quality of aluminum alloys and environmental protection and energy saving are getting higher and higher, and people have begun to adopt some vacuum treatment methods, such as ion nitriding, ion oxygenation and ion implantation. Such as: Fu-Hsing Li of Taiwan, China, etc., using a 13.6MHz radio frequency ion device, oxidation for 2h can prepare a crystalline alumina layer with a thickness of about 60nm on the aluminum surface (Lu F H, Tsai HD, Chieh YC. Plasma oxidation of Al thin films on Si substrates. Thin Solid Films, 2008, 516(8):1871-1876). Raveh et al. in Germany used microwave ion oxidation technology to prepare 20nm thick amorphous aluminum oxide layer (Raveh A, Tsameret Z K, Grossman E. Surface characterization of thin layers of aluminum oxide. Surface and Coatings Technology, 1997, 88(1): 103-111 ).

There are also hollow cathode discharge assisted ion oxidation treatment of aluminum alloys in China (Li Yang, Zhang Nianwu, Xu Huizhong, Qiu Jianxun, Zhao Xiangjin, Wang Shuo, Research on Aluminum Alloy Hollow Cathode Discharge Assisted Ion Oxidation Technology, Journal of Yantai University (Natural Science and Engineering Edition), 2014 , 27(4): 271-274), to prepare a dense and smooth oxide layer (Al ₂ O ₃ ) with a thickness of 20-500 nm. Immersion corrosion experiments were carried out on the untreated and ion-oxidized samples in NaCl solution with a concentration of 3.5wt%. After soaking for 20 days, the untreated samples were severely corroded, while the surface of the oxidized samples had no obvious corrosion phenomenon. In general, ion oxygen infiltration can effectively improve the corrosion resistance of aluminum alloys, but the thickness of the oxide layer is still thin, and its thickness still needs to be improved.

SUMMARY OF THE INVENTION

Aiming at the deficiencies of the existing aluminum and aluminum alloy oxidation technologies, the purpose of the present invention is to provide a method for plasma oxidation of aluminum and aluminum alloy surfaces, which can effectively improve the corrosion resistance of aluminum alloys and increase the thickness of the oxide layer. .

In order to achieve the above object, the technical scheme of the present invention is:

A plasma oxidation method of aluminum and aluminum alloy surfaces, which adopts arc-enhanced glow discharge technology to realize plasma oxidation of aluminum and aluminum alloy surfaces.

In the method for surface plasma oxidation of aluminum and aluminum alloys, when the arc-enhanced glow discharge technology is adopted, an auxiliary anode is arranged outside the arc cathode target, and the auxiliary anode is cooled by water; the auxiliary anode is made of oxygen-free copper, and is connected with the arc. source and cathode are connected.

In the method for plasma oxidation of aluminum and aluminum alloy surfaces, in the process of plasma oxidation by arc-enhanced glow discharge technology, the substrate is connected to the positive electrode of the bias power supply, and the wall of the vacuum chamber is connected to the negative electrode of the bias power supply.

Described aluminum and aluminum alloy surface plasma oxidation method, concrete steps are as follows:

(1) Substrate pre-cleaning: After sandblasting, the substrate surface is ultrasonicated in alcohol solution for 1 to 30 minutes, dried by hot air, and then loaded into the workpiece rack in the vacuum chamber, waiting for processing;

(2) Argon ion bombardment: using pure titanium target, when the vacuum degree in the vacuum chamber reaches 1×10 ^-3 Pa～1×10 ^-2 Pa, heat the vacuum chamber to 200～500℃; pass argon gas into the vacuum chamber , the argon gas pressure is controlled between 0.1~5Pa; at the same time, the pure titanium target arc source is turned on, and the arc current is 60~150A. After the pure titanium target arc discharge, an electron flow will be generated, ionizing the argon gas, and applying a pulse negative bias to the matrix. In the range of -400~-1500V, the duty cycle of the bias voltage is in the range of 30~90%, so that the argon gas glow discharges, and the substrate is glow cleaned for 10~120 minutes;

(3) Plasma oxidation: use a pure titanium target, adjust the argon gas pressure within the range of 0.1-5Pa, and at the same time feed oxygen, the argon gas flow rate is within the range of 100-1000sccm, and the oxygen gas flow rate is within the range of 5-50% of the argon gas flow rate Inside, a pulse positive bias voltage of 10V-500V is applied to the substrate, and the bias duty cycle is within the range of 10-80%; the arc current is adjusted to 60-150A, and the oxidation time is 10-300 minutes;

(4) After the oxidation is completed, stop the arc, stop the pulse bias of the substrate, stop feeding argon and oxygen, continue to vacuumize, the workpiece is cooled to below 100 ℃ with the furnace, open the vacuum chamber, take out the workpiece, and the oxidation process is over.

In the method for surface plasma oxidation of aluminum and aluminum alloys, after the oxidation process is completed, the thickness of the oxide layer ranges from 0.01 to 2 microns.

The design idea of the present invention is:

On the basis of glow discharge, the present invention utilizes arc discharge enhancement to further increase plasma density, thereby increasing the thickness of the oxide layer. The invention adopts arc enhanced glow discharge (AEGD) technology to complete, generates electron flow through arc discharge, and then the electrons collide with oxygen and other gases to make them ionized to generate oxygen plasma, and a positive bias electric field is applied on the surface of the substrate to generate glow After discharge, the negatively charged oxygen ions are attracted to the surface of the substrate for oxidation reaction, thereby forming an aluminum oxide protective film layer.

Compared with the prior art, the advantages and beneficial effects of the present invention are:

1. The present invention adopts arc-enhanced glow discharge (AEGD) technology to realize plasma oxidation of aluminum and aluminum alloy surfaces. Compared with anodic oxidation and micro-arc oxidation, it has the advantages of no pollution to the environment, fast oxidation speed, and obtains the thickness of the oxide layer. Thicker and so on.

2. The oxide layer prepared by the method of the present invention can effectively improve the pitting corrosion resistance of the aluminum alloy in the marine environment.

3. In the present invention, an auxiliary anode is arranged on the outside of the arc cathode target, and the auxiliary anode is cooled by water. The function of the auxiliary anode is to attract negatively charged electrons, and ionize the gas through the collision of the electrons with the gas molecules.

Detailed ways:

Hereinafter, the present invention will be further described in detail through examples.

Example 1

In this embodiment, pure aluminum is used as the base material, the size of the sample block is 20 mm×10 mm×10 mm, and the size of the oxidized surface is 20 mm×10 mm. Before oxidation, the surface of the substrate is ground and polished, ultrasonically cleaned in alcohol solution for 10 minutes, dried, and placed on the workpiece rack in the vacuum chamber. When the vacuum degree in the vacuum chamber reaches 4×10 ^-3 Pa, the vacuum chamber is heated. When the temperature reaches 350°C, turn on the gas mass flow controller, pass argon gas into the vacuum chamber, set the argon gas flow rate to 500sccm, and control the air pressure to 3.0Pa. At the same time, turn on the pure titanium target arc source, the arc current is 80A, and the pure titanium target generates After the arc discharge, electron flow will be generated, ionizing the argon gas, the matrix will be pulsed with a negative bias voltage of -700V, and the bias duty ratio will be 70%, so that the argon gas will undergo glow discharge, and the matrix will be glow cleaned for 40 minutes; then Adjust the argon gas pressure to 2.0Pa, and feed oxygen at the same time, the oxygen flow rate is 20% of the argon gas flow rate, apply a pulse positive bias voltage of 200V to the substrate, and the bias duty cycle is 30%; adjust the arc current to 80A, and the oxidation time is 90 minutes; after the oxidation, stop the arc, stop the pulse bias of the substrate, stop the gas supply, continue to vacuum, the workpiece is cooled to below 100 ℃ with the furnace, open the vacuum chamber, take out the workpiece, and the oxidation process is over.

The appearance of the obtained oxide layer is silver-gray, and the thickness of the oxide layer measured by scanning electron microscope is 0.4 μm.

Example 2

In this embodiment, the base material is aluminum alloy (brand 2024), the size of the sample is 20mm×10mm×10mm, and the size of the oxidized surface is 20mm×10mm. Before oxidation, the surface of the substrate is ground and polished, ultrasonically cleaned in alcohol solution for 15 minutes, dried, and placed on the workpiece rack in the vacuum chamber. When the vacuum degree in the vacuum chamber reaches 2×10 ^-3 Pa, the vacuum chamber is heated. When the temperature reaches 450°C, turn on the gas mass flow controller, pass argon gas into the vacuum chamber, set the argon gas flow rate to 350sccm, and control the air pressure to 2.0Pa. At the same time, turn on the pure titanium target arc source, the arc current is 90A, and the pure titanium target generates After the arc discharge, electron flow will be generated, ionizing the argon gas, the substrate will be pulsed with a negative bias voltage of -800V, and the bias duty cycle will be 60%, so that the argon gas will undergo glow discharge, and the substrate will be glow cleaned for 60 minutes; then Adjust the argon gas pressure to 1.5Pa, and feed oxygen at the same time, the oxygen flow rate is 15% of the argon gas flow rate, apply a pulse positive bias voltage of 150V to the substrate, and the bias duty ratio is 25%; adjust the arc current to 80A, and the oxidation time is 120 minutes; after the oxidation, stop the arc, stop the pulse bias of the substrate, stop the gas supply, continue to vacuumize, the workpiece is cooled to below 100 ℃ with the furnace, open the vacuum chamber, take out the workpiece, and the oxidation process is over.

The appearance of the obtained oxide layer is silver-gray, and the thickness of the oxide layer measured by scanning electron microscope is 0.5 μm.

Example 3

In this embodiment, the base material is aluminum alloy (the grade is 6061), the size of the sample is 20mm×10mm×10mm, and the size of the oxidized surface is 20mm×10mm. Before oxidation, the surface of the substrate is ground and polished, ultrasonically cleaned in alcohol solution for 20 minutes, dried, and placed on the workpiece rack in the vacuum chamber. When the vacuum degree in the vacuum chamber reaches 6×10 ^-3 Pa, the vacuum chamber is heated. When the temperature reaches 400°C, turn on the gas mass flow controller, pass argon gas into the vacuum chamber, set the argon gas flow rate to 600sccm, and control the air pressure to 3.5Pa. At the same time, turn on the pure titanium target arc source, the arc current is 100A, and the pure titanium target generates After the arc discharge, electron flow will be generated, ionizing the argon gas, the matrix will be pulsed with a negative bias voltage of -600V, and the bias duty cycle will be 80%, so that the argon gas will undergo glow discharge, and the matrix will be glow cleaned for 60 minutes; then Adjust the argon gas pressure to 2.5Pa, and feed oxygen at the same time, the oxygen flow rate is 20% of the argon gas flow rate, apply a pulse positive bias voltage of 200V to the substrate, and the bias duty ratio is 20%; adjust the arc current to 90A, and the oxidation time is 180 minutes; after the oxidation, stop the arc, stop the pulse bias of the substrate, stop the gas supply, continue to vacuumize, the workpiece is cooled to below 100 ℃ with the furnace, open the vacuum chamber, take out the workpiece, and the oxidation process is over.

The appearance of the obtained oxide layer is silver-gray, and the thickness of the oxide layer measured by scanning electron microscope is 0.9 μm.

Example 4

In this embodiment, the base material is aluminum alloy (the grade is 7075), the size of the sample is 20mm×10mm×10mm, and the size of the oxidized surface is 20mm×10mm. Before oxidation, the surface of the substrate is ground and polished, ultrasonically cleaned in alcohol solution for 25 minutes, dried, and placed on the workpiece rack in the vacuum chamber. When the vacuum degree in the vacuum chamber reaches 2×10 ^-3 Pa, the vacuum chamber is heated. When the temperature reaches 500°C, turn on the gas mass flow controller, pass argon gas into the vacuum chamber, set the argon gas flow rate to 300sccm, and control the air pressure to 1.8Pa. At the same time, open the pure titanium target arc source, the arc current is 100A, and the pure titanium target generates After the arc discharge, electron flow will be generated, ionizing the argon gas, the matrix will be pulsed with a negative bias voltage of -900V, and the bias duty cycle will be 70%, so that the argon gas will undergo glow discharge, and the matrix will be glow cleaned for 60 minutes; then Adjust the argon gas pressure to 1.8Pa, and feed oxygen at the same time, the oxygen flow rate is 25% of the argon gas flow rate, apply a pulse positive bias voltage of 250V to the substrate, and the bias duty ratio is 30%; adjust the arc current to 70A, and the oxidation time is 150 minutes; after the oxidation, stop the arc, stop the pulse bias of the substrate, stop the gas supply, continue to vacuumize, the workpiece is cooled to below 100 ℃ with the furnace, open the vacuum chamber, take out the workpiece, and the oxidation process is over.

The appearance of the obtained oxide layer is silver gray, and the thickness of the oxide layer measured by scanning electron microscope is 0.8 μm.

The results of the examples show that the method for plasma oxidation of aluminum and aluminum alloy surfaces of the present invention has the advantages of no environmental pollution compared with traditional micro-arc oxidation and anodic oxidation technologies, and can effectively improve the resistance of the aluminum alloy surface. corrosion performance.

Claims (5)

1. A method for plasma oxidation of aluminum and aluminum alloy surface, it is characterized in that, adopts arc enhanced glow discharge technology to realize the plasma oxidation of aluminum and aluminum alloy surface. 2. according to the method for surface plasma oxidation of aluminum and aluminum alloy according to claim 1, it is characterized in that, when adopting arc enhanced glow discharge technology, an auxiliary anode is arranged outside the arc cathode target, and the auxiliary anode is cooled by water; The auxiliary anode is made of oxygen-free copper and is connected to the arc source cathode. 3. according to the method for plasma oxidation of aluminum and aluminum alloy surface according to claim 1, it is characterized in that, in the process of plasma oxidation using arc-enhanced glow discharge technology, the substrate is connected to the positive electrode of the bias power supply, and the wall of the vacuum chamber is connected to the bias voltage Negative power supply. 4. according to the described aluminum and aluminum alloy surface plasma oxidation method of one of claim 1 to 3, it is characterized in that, concrete steps are as follows: (1) Substrate pre-cleaning: After sandblasting, the substrate surface is ultrasonicated in alcohol solution for 1 to 30 minutes, dried by hot air, and then loaded into the workpiece rack in the vacuum chamber, waiting for processing; (2) Argon ion bombardment: using pure titanium target, when the vacuum degree in the vacuum chamber reaches 1×10 ^-3 Pa～1×10 ^-2 Pa, heat the vacuum chamber to 200～500℃; pass argon gas into the vacuum chamber , the argon gas pressure is controlled between 0.1~5Pa; at the same time, the pure titanium target arc source is turned on, and the arc current is 60~150A. After the pure titanium target arc discharge, an electron flow will be generated, ionizing the argon gas, and applying a pulse negative bias to the matrix. In the range of -400~-1500V, the duty cycle of the bias voltage is in the range of 30~90%, so that the argon gas glow discharges, and the substrate is glow cleaned for 10~120 minutes; (3) Plasma oxidation: use a pure titanium target, adjust the argon gas pressure within the range of 0.1-5Pa, and at the same time feed oxygen, the argon gas flow rate is within the range of 100-1000sccm, and the oxygen gas flow rate is within the range of 5-50% of the argon gas flow rate Inside, a pulse positive bias voltage of 10V-500V is applied to the substrate, and the bias duty cycle is within the range of 10-80%; the arc current is adjusted to 60-150A, and the oxidation time is 10-300 minutes; (4) After the oxidation is completed, stop the arc, stop the pulse bias of the substrate, stop feeding argon and oxygen, continue to vacuumize, the workpiece is cooled to below 100 ℃ with the furnace, open the vacuum chamber, take out the workpiece, and the oxidation process is over. 5 . The method for surface plasma oxidation of aluminum and its aluminum alloy according to claim 4 , wherein after the oxidation process is completed, the thickness of the oxide layer ranges from 0.01 to 2 microns. 6 .