KR20050014211A - microarc oxidation - Google Patents

Abstract

PURPOSE: To provide an improved metal surface oxidation process capable of refining oxidation grains and maintaining structure densification so that an uniformly thick film having high density is formed by applying high frequency to the surface of metal in a microarc oxidation process. CONSTITUTION: A microarc oxidation process of aluminum alloy articles comprises a step of loading an aluminum alloy member in a bath containing a weak alkaline electrolyte comprising 0.05 to 10% of potassium hydroxide and sodium silicate; and a step of repeatedly performing operation under the conditions that a voltage is controlled to a range of -200 to 1,500 V, a current density is controlled to a range of 1 to 200 A/dm¬2, an impulse time is controlled to a range of 0.01 msec to 0.01 sec, and impulse intervals are controlled to a range of 0.01 msec to 0.01 sec, wherein carbide powder, nitride or metal oxide are added to the electrolytic bath, and wherein the impulse is converted in such a way that "+" impulses and "-" impulses are alternately used within a range of 1:1 to 9:9.

Description

Microarc oxidation of articles made of aluminum alloys

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microarc oxidation process of an article made of an aluminum alloy. In particular, the anodization process for forming an oxide film on a metal surface includes an electrode member made of an aluminum alloy in an electrolytic cell containing a weak alkali electrolyte. Electrochemical oxidation process using high frequency (-200 ~ 1000V voltage and 100 ~ 10000Hz frequency) characteristics in the loaded state makes oxide particles fine and maintains compactness of tissue, and improves wear resistance and corrosion resistance by fast operation. I would have to.

The present invention relates to the automotive industry (automotive engine casings, pistons, exterior finishing parts), as well as the construction industry (windows, ceilings, commercial tents), aircraft industry (aircraft exterior surface materials, engine parts, turbines), machinery and oil refining industries ( Microarc oxidation process useful for corrosion protection of articles in pump parts, case parts).

In general, all metals exhibiting the properties of aluminum, titanium, alloys thereof, and vacuum tubes (diodes) are due to their excellent strength / weight properties, which are particularly important in aeronautics, automotive and mechanical engineering (particularly in moving parts with high mechanical loads and deformations). It is used variously).

The materials have been coated on the surface in such a way as to increase the mechanical properties (surface hardness, coefficient of friction, wear resistance, etc.).

Surface coatings must be able to meet complementary requirements such as corrosion resistance in acidic and / or alkaline media, the ability to withstand high temperatures instantaneously, or attain dielectric properties.

Aluminum, in particular, is so active that its surface is naturally oxidized in air. Therefore, in the case of aluminum or aluminum alloy products, a protective oxide film is formed through an anodizing process that artificially anodizes the surface of the product.

When the aluminum anodized film has a predetermined thickness, a porous layer is formed in which numerous small holes are formed. When the anodized film activated by such a porous layer is left in a pore state, the anodized film reacts with a gas in the air, and thus the corrosion resistance of the anodized film is reduced, so that it is sealed to obtain a stable anodized film.

Therefore, in the conventional electrolytic coating process, anodizing method is used for protection from wear and tear, and this anodizing process is used to form a protective oxide film on an aluminum material. However, coatings made in this way are limited in thickness and have only moderate hardness (up to about 500 Hv).

In addition, in anodizing, a separate wastewater treatment facility was required by using about 56% of strong acidic electrolyte solution. It needs to be wide and keeps the temperature of electrolyte at about 0 ℃, so the coating is good, so cooling equipment is needed.

And hard anodizing has been used to achieve high performance coatings or especially surface hardness to withstand more intense operating conditions.

The conventional hard anodizing method has a difficulty in working in a low temperature (-3 to 3 ° C) environment in an electrolyte of strong acid (60% sulfuric acid electrolyte), and pretreatment such as degreasing, pickling, chemical polishing, and main treatment and residual There is a disadvantage that requires several processes of post-treatment for chemical removal.

In addition, it took about 8 hours to obtain a coating time of about 80 μ, and the characteristics of the film thus obtained also had problems in corrosion resistance and hardness.

In order to compensate for such drawbacks, Korean Patent Laid-Open Publication No. 2003-11316 proposes an electrical oxidation process using micro arc oxidation (M.A.O).

The M.A.O method is a method of giving a positive / negative pulse using a frequency voltage of 20 mSec when rectifying 60 Hz (about 20 ms) of electricity into a weak alkaline electrolyte. This method has the advantage of increasing the wear resistance and reducing the amount of pores to increase the corrosion resistance, while having a lot of power consumption and rough surface roughness.

The present invention solves the conventional problems as described above, and an object of the present invention is to provide a high frequency to the metal surface in the micro arc oxidation treatment (MAO) method to refine the oxide particles to form a thick and uniform thick film And an improved metal surface oxidation process to maintain the compactness of the tissue.

In addition, the present invention has a further object to allow the coating layer to be dense and greatly reduce the amount of pores by gradually changing the ratio of "+" particles and "-" particle impulses to improve coating properties.

According to the above object, the oxidation process of the present invention loads a member made of an aluminum alloy into a bath containing a weak alkali electrolyte, and has a high voltage (-200 to 1000 V) and a frequency (100 to). 10000 Hz) is generated, the impulse time is 0.05mSec ~ 0.001Sec, the interval between the impulse is characterized by the microarc oxidation process to operate repeatedly 0.05mSec ~ 0.002Sec pause time.

In addition, the present invention is characterized in that the oxide particles on the metal surface are made fine while gradually changing the ratio of the "+" particles and the "-" particle impulses, and greatly increase the wear resistance and corrosion resistance.

In addition, in the weak alkali electrolyte used in the anodizing process of the present invention, an aqueous solution of an alkali metal such as 0.05-10% potassium hydroxide and a sodium silicate salt of an alkali metal are used.

Carbide powder and nitride or metal oxide are added to the electrolytic cell.

The present invention configured as described above has the greatest effect by selecting the appropriate capacity of the aluminum member which is the maximum amount of anion from the electrolyte and can be loaded into the electrolyte bath when the surface charge is formed on the surface of the object to be coated. Select the pause between pulses to get.

In addition, the maximum number of ions generated from the electrolyte is obtained when the pause time between pulses is in the range of 0.05 mSec to 0.002 Sec, and the current density is adjusted to be 2 to 200 A / dm² to immerse the member in the electrolyte bath.

The electrolyte uses a weak alkaline electrolyte. Although electrolytes are affected by the type of alloy, the shape of the product and the use of the product, a weak alkaline electrolyte with an integrated concentration of 0.05 to 10% is used, and the solvents of the weak electrolyte are potassium hydroxide and sodium silicate salt.

The process of current flow in the electrolyte is an inertial process, especially in pulsed operation. When the pulse operation is stopped, ions before the electrode layer continue to move for some time by their own momentum to form charge on the surface of the electrode layer, and the charge value is influenced by the time (ie, the rest time) at which the charge is formed.

This is because a short dwell time leaves no time for charge to be fully formed, and prolonging the dwell time results in a flow of charge down from the component surface in the electrolyte and increases power consumption.

The actual current density supplied to the component surface exceeds the current value set from the power source, so the area can be reduced using a -200 to 1000 V pulse generator to obtain coatings of equal thickness (having the same characteristics). Use an alloy plate of 2 to 200 A / dm².

The maximum limit of loading depends on the plant technical capabilities (transformer power, jaw size, operating reliability of the power unit, current supply components, etc.).

Example 1

The aluminum alloy member is submerged and loaded into a bath containing a weak alkali electrolyte. At this time, the electrolyte in which the aluminum member is immersed is prepared in an aqueous solution of 0.05-5% of potassium hydroxide and sodium silicate salt.

Voltage is -200 ~ 1000V,

Current density is 2 ~ 200 A / dm²

Impulse time is 0.05mSec ~ 0.001Sec,

The interval between the impulses is repeated to form an oxide film in the range of 0.05mSec to 0.002Sec.

Under the above conditions, the impulse of the electrolytic cell is preferably generated for 0.8 mSec, and the rest time between the impulses is set to 1.2 mSec. Initially, only "+" impulse is given to one electrode for 1 minute and the "-" impulse is It maintains the idle state (1: 0 state) which is not provided.

Thereafter, the "+" impulse and the "-" impulse are gradually changed, that is, the optimum ratio of 1: 1 to 9: 9 is found and operated under the condition of converting the "+" impulse and the "-" impulse.

As such, the present invention provides a process that can electrically and chemically oxidize the aluminum or magnesium surface to form a physically-mechanically enhanced coating while maintaining an environmentally friendly operation process, thereby miniaturizing the oxidized particles so that the density of the tissue can be improved. It is possible to increase wear resistance and corrosion resistance by maintaining and fast operation.

As described above, according to the present invention, the present invention does not require a waste water treatment facility by using a weak alkali electrolyte in the electrolytic cell in forming the oxide film, and the oxide film forming work is well performed after the pretreatment (degreasing) and the post-treatment is performed. There is no need for a process, and there is an advantage that automatic control is possible.

In addition, the present invention can control the "+" impulse and "-" impulse value at a constant rate during the electrolysis using a high frequency to maintain the compactness of the oxide particles and maintain the compactness of the tissue, and thus the wear and corrosion resistance in a fast operation It can be increased.

Claims (3)

A member made of aluminum alloy was loaded into a bath containing a weak alkaline electrolyte consisting of 0.05-10% potassium hydroxide and sodium silicate salt. Voltage is -200 ~ 1500V, Current density is 1 ~ 200 A / dm² Impulse time is 0.01mSec ~ 0.01Sec, The interval between impulses is 0.01mSec ~ 0.01Sec, Microarc oxidation process of an article made of an aluminum alloy, characterized by repeated operation within the range. 2. The microarc oxidation process of an article made of an aluminum alloy according to claim 1, wherein the electrolytic bath is added with carbide powder and nitride or metal oxide. The process of claim 1, wherein the impulse converts and uses "+" impulse and "-" impulse within a range of 1: 1 to 9: 9.