CN1749444A - A method of plasma micro-arc oxidation on the surface of light metal - Google Patents

Abstract

The present invention relates to plasma micro arc oxidizing process of light metal surface, and is especially surface oxidizing technological process for aluminum and aluminum alloy. The technological process adopts asymmetrical positive and negative pulse electric sources with continuously adjustable peak voltage, continuously adjustable pulse duty factor and frequency continuously adjustable in 20-2000 Hz; the pre-treated workpiece hung to anode and set inside electrolyte; stainless sheet suspended inside the electrolyte tank as cathode; neutral or alkaline electrolyte comprising metal silicate or metal phosphate and deionized water; and gas-liquid scanning treatment process, in which the workpiece to be oxidized is made to move back and forth in homogeneous speed inside the electrolyte for plasma micro arc discharge in the gas-liquid interface to form oxide film. The process is reliable, high in oxidation efficiency, high in metal surface treating performance and low in power consumption.

Description

A method of plasma micro-arc oxidation on the surface of light metal

Technical field:

The invention relates to a method for performing plasma micro-arc oxidation on the surface of light metals, in particular to a process for oxidation treatment of the surface of aluminum and its alloys, that is, performing plasma micro-arc oxidation treatment on the surface of aluminum and its alloys to make it A ceramic coating is formed on the surface, which can be widely used in the fields of machinery, electronics, aviation, automobiles, engineering, etc. to protect magnesium, titanium and its alloys, especially aluminum and its alloy accessories.

technical background:

Aluminum and its alloys have good mechanical and physical properties. They can be widely used in machinery, electronics, aviation, automobiles, engineering and other fields, and play an important role in the national economy. Although there is a layer of natural oxide film on the surface of aluminum, it is only about 10-100nm and cannot protect it. Therefore, it is very important to treat the surface of the aluminum material to form an oxide film on the surface to improve the surface hardness and corrosion resistance of the aluminum material. At present, the surface oxidation methods of aluminum mainly include: chemical oxidation, anodic oxidation and micro-arc oxidation. Compared with chemical oxidation and anodic oxidation, micro-arc oxidation has many advantages: simple pretreatment, fast film growth rate, high hardness, and electrolyte is not easy to pollute the environment, etc. Therefore, micro-arc oxidation technology is more and more widely used. There are already many patent documents or articles recorded, such as in the document published by Chinese Patent Application No. 011022620, a pulse power supply is used, the pulse waveform is a square wave, the frequency is 25-300Hz, the applied voltage is a positive pulse voltage of 300-800V and 0 Negative pulse voltage of -300V; in the records published in Chinese patent application No. 031571735, symmetrical AC pulses are used, the voltage is 180-270V, the frequency is 20-200Hz, and the duty ratio is 0.1-0.7. The above-mentioned patents mentioned that the pulse frequency is below 300 Hz, and did not indicate how much the pulse peak voltage is and whether the duty factor is continuously adjustable respectively. Russian patent RU2110624 records that the process parameters are optimized by gradually removing the sample anode from the molten electrolyte, but the patent does not point out that the electrolyte is gradually put into the electrolyte, and it goes back and forth multiple times. In the literature records of Chinese patent application number 022220631, a device for surface treatment of the inner hole of a part is described, but a relatively complicated device is required, and only the inner surface of the hole can be treated, and the inner and outer surfaces of the hole cannot be treated at the same time. In addition, there are Chinese patent application numbers 998168645, 021115214, 971824800, and "Aluminum Alloy Micro-arc Oxidation Technology" on page 138 of the second issue of "Journal of Xi'an University of Technology" in 2000, all of which are described and recorded from the same principle and method framework. A method and equipment for oxidizing the surface of aluminum and its alloys have been disclosed. These methods have some disadvantages that are not easy to improve efficiency and increase processing performance to varying degrees.

Invention content:

The object of the present invention is to adopt the method for carrying out oxidation treatment on the surface of metal especially aluminum and its alloy by adopting conventional technical process, it is mainly in order to overcome the shortcoming in the parameter condition aspect existing in the prior art, in improving efficiency and increasing processing performance Under the conditions, a new method of using plasma micro-arc oxidation to treat the surface of aluminum and its alloys is provided, that is, an asymmetric positive and negative pulse power supply is used for plasma micro-arc oxidation to treat aluminum and its alloys.

The plasma micro-arc oxidation process of the oxidation method involved in the present invention is as follows: hang the pretreated workpiece on the anode and put it into the electrolyte, and the cathode is a stainless steel sheet suspended in a stainless steel electrolyte tank or a plastic electrolyte tank; Symmetrical positive and negative pulse power supply, applied pulse forward voltage is 0-650V, negative voltage is 0-100V, current density is 3-60A/dm ² , oxidation treatment temperature is 10-65℃, treatment time can be 5- 360min. Among them, the pulse frequency is continuously adjustable from 20-2000Hz; the positive and negative pulse peak voltages are continuously adjustable: the positive peak voltage is 0-700V, the negative peak voltage is 0-100V; the positive and negative pulse duty factors are respectively 0-100 % is continuously adjustable. The electrolyte used is composed of chemical substances such as metal salts and deionized water, which is divided into silicate series and phosphate series, which are neutral or alkaline, and the pH value is 7-12. The silicate series electrolyte includes sodium silicate (2.5-60g/L), sodium hydroxide (0.5-10g/L), additives (sodium hexametaphosphate, potassium sodium tartrate, sodium tungstate, sodium citrate, etc. organic or inorganic) 0.5-5g/L. The phosphate series electrolyte includes sodium dihydrogen phosphate (30-160g/L), sodium tetraborate (10-80g/L), sodium fluoride (8-25g/L) and additives (potassium sodium tartrate, sodium tungstate , sodium fluoride, ammonium fluoride and other organic or inorganic substances) 0.5-5g/L.

The plasma micro-arc oxidation method used in the present invention treats the surface of aluminum and its alloys. In addition to immersing the workpiece in the electrolyte, it can also be carried out by using a gas-liquid scanning method (gas-liquid interface scanning method), so that the oxidized workpiece can be oxidized at a temperature of 0.04- The speed of 0.4mm/s is gradually immersed in the electrolyte at a constant speed, and then gradually leaves the electrolyte at the same speed and goes back and forth several times, which can make the plasma micro-arc discharge occur at the gas-liquid interface, so that the discharge energy is relatively concentrated Arc discharge scans the sample line, which is beneficial to the formation of oxide film on the workpiece.

The present invention uses the plasma micro-arc oxidation method to simultaneously treat the inner and outer surfaces of the aluminum alloy workpiece with holes, because the inner surface of the hole of the aluminum alloy workpiece with holes is partially shielded by the electric field, so the oxide film layer on the inner surface is not easy to grow well, Auxiliary cathodes are added in the workpiece hole (the minimum aperture is Φ18mm), so that a good oxide film layer can be obtained on the inner and outer surfaces of the workpiece hole at the same time.

In the present invention, when the plasma micro-arc oxidation method is used to treat the surface of aluminum and its alloys, the surface of the used hanger is insulated, and the anode hanger is used to apply insulating tape or insulating coating to the part of the hanger from the workpiece to the electrolyte. The insulating material is stretched and insulated to reduce the scattered current and avoid gas explosion and electrolyte splashing on the electrolyte liquid surface. Compared with the existing methods, the present invention adjusts parameters such as frequency on the basis of the same principle and framework, adopts the gas-liquid interface scanning method to simultaneously process the inner and outer surfaces of the workpiece, adds auxiliary cathodes and adopts technical measures such as insulation treatment , and its implementation results show that this method has the advantages of reliable principle, high oxidation treatment efficiency, good metal surface performance, and energy saving.

Specific examples:

In the implementation of the present invention, hang the pretreated workpiece on the anode and put it into the electrolyte solution prepared respectively. Carry out oxidation treatment under a variety of different conditions, its condition parameter is as each embodiment, and its oxidation treatment result all reaches ideal effect.

Example 1:

Processed workpiece: measuring instrument aluminum alloy parts

Material model: duralumin LY12

Electrolyte formula: sodium silicate 10g/L

Sodium Hydroxide 2.5g/L

                                                                                ,

                                                            

Oxidation conditions: frequency 400Hz

Voltage: positive pulse peak voltage 400V

Negative pulse peak voltage 30V

Duty factor 50%

Current density 8A/ ^dm2

Time 10min

Result: The film layer is dark gray, uniform and smooth, and the film thickness is 8 μm, which meets the requirements for use

Example 2:

Material model: duralumin LY12

Electrolyte formula: sodium silicate 10g/L

Sodium hydroxide 2.5g/L

Sodium borate 5g/L

Sodium Tungstate 2g/L

                             

Oxidation conditions: frequency 400Hz

Voltage: positive pulse peak voltage 500V

Negative pulse peak voltage 40V

Duty factor 50%

Current density 15A/ ^dm2

Time 360min

Result: film thickness 200μm

     Film Hardness      HV2200

Example 3:

The inner hole part (Φ18mm×50mm) is selected as the processing workpiece.

Material model: deformed aluminum 8011

Electrolyte formula: sodium silicate 15g/L

Sodium Hydroxide 5g/L

Sodium hexametaphosphate 2g/L

                                                                                                         

                                                                    

Oxidation conditions: frequency 400Hz

Voltage: positive pulse peak voltage 300V

Negative pulse peak voltage 65V

Duty factor 30%

Current density 8A/ ^dm2

    Auxiliary cathode   The diameter is 3mm stainless steel wire

Time 10min

Result: The inner and outer surface film layers are light gray, uniform in color, and the thickness of the smooth surface film layer is 6 μm

Example 4:

Aluminum alloy hood parts are selected as the processing workpiece.

Material model: duralumin LY12

Electrolyte formula: sodium dihydrogen phosphate 60g/L

Sodium Tetraborate 40g/L

Sodium Fluoride 20g/L

                                                                                             

Sodium Tungstate 3g/L

                               

Oxidation conditions: frequency 100Hz

Voltage: positive pulse peak voltage 180V

Current density 10A/ ^cm2

Duty factor 50%

Time 10min

Result: The color of the film layer is white, and the surface is fine and smooth

Film thickness 9μm

  Film hardness HV 1200

Example 5:

Material model: duralumin LY12

Electrolyte formula: sodium dihydrogen phosphate 80g/L

Sodium Tetraborate 40g/L

Sodium Fluoride 20g/L

                                                                               

                               

Oxidation conditions: frequency 100Hz

Voltage positive pulse peak voltage 170V

Current density 10A/ ^dm2

Duty factor 10%

Time 7min

Results: The color of the film is white, the surface is smooth and delicate, and the thickness of the film is 10 μm. Under the scanning electron microscope

Observation, there are micropores with a diameter of 5-10 μm on the surface of the membrane layer

Embodiment 6:

Material model: duralumin LY12

Electrolyte formula: sodium dihydrogen phosphate 80g/L

Sodium Tetraborate 40g/L

Sodium Fluoride 20g/L

                                                                              

                               

Oxidation conditions: frequency 100Hz

Voltage Positive Pulse Peak Voltage 170V

Current density 10A/ ^dm2

Duty factor 50%

                             

Results: The color of the film is white, the surface is relatively smooth, and the thickness of the film is 10 μm. Observed under the scanning electron microscope

Observation shows that there are micropores with a diameter of 15-25 μm on the surface of the membrane layer.

It can be seen from the results of the example that when other conditions are the same, the smaller the pulse duty factor, the denser the resulting film. When the duty factor is reduced from 50% to 10%, the diameter of the micropores on the surface of the film layer is reduced from 15-25 μm to 5 -10 μm.

Claims (5)

1. method of light metal surface being carried out plasma micro-arc oxidation, to hang over through the workpiece of pre-treatment and put into electrolytic solution on the anode, negative electrode is the stainless steel substrates that hangs in stainless steel electrolytic liquid bath or the plastics electrolytic bath, adopt the asymmetric positive and negative pulse power, it is characterized in that pulse-repetition is that 20-2000HZ is adjustable continuously, the positive negative pulse stuffing crest voltage is adjustable continuously, and the positive negative pulse stuffing stacking factor is adjustable continuously in 0-100%.

2. according to claim 1 the method for plasma micro-arc oxidation is carried out in the metallic surface, it is characterized in that used silicate series electrolytic solution comprises water glass, sodium hydroxide and additive; Used series of phosphate electrolytic solution comprises SODIUM PHOSPHATE, MONOBASIC, sodium tetraborate, Sodium Fluoride and additive.

3. method of the metallic surface being carried out plasma micro-arc oxidation according to claim 1, except that workpiece being immersed in carry out in the electrolytic solution, also can adopt the liquid-gas interface scanning method that workpiece is carried out oxide treatment, it is characterized in that making oxidized workpiece at the uniform velocity little by little to enter electrolytic solution, at the uniform velocity little by little leave electrolytic solution with identical speed again, and come and go repeatedly.

4. according to claim 1 the method for plasma micro-arc oxidation is carried out in the metallic surface, it is characterized in that workpiece surfaces externally and internally with holes is handled simultaneously, in workpiece hole, increase auxiliary cathode.

5. according to claim 1 the method for plasma micro-arc oxidation is carried out in the metallic surface, it is characterized in that insulation processing is carried out with insulation tape or insulating coating in the position on hanger is from the workpiece to electrolytic solution.