RU2447202C1 - Method of producing magnesium alloy-based protective coats - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: proposed method comprises electrochemical treatment at current density of 5-25 A/dm² and ratio of polarisation voltage anode and cathode amplitudes U_a/U_c equal to 2-4 in electrolyte containing, in g/l: sodium silicate - 5-15, alkaline metal hydroxide - 2-12, sodium vanadate - 0.2-1.0, azimido-benzene - 0.2-1.0, and water in amount of up to 1 l.

EFFECT: lower power consumption, higher antirust properties and fire resistibility.

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Description

The invention relates to the production of protective coatings on magnesium alloys by electrochemical processing of magnesium alloys by microarc oxidation and can find application in mechanical engineering, aircraft manufacturing, computer technology and automotive industry.

A known method of producing protective coatings on magnesium alloys, including a two-stage electrochemical treatment by microarc oxidation, followed by electroplating. Microarc oxidation is carried out at a constant anode current density of 5-10 A / dm ² in an electrolyte solution containing sodium silicate, sodium phosphate and sodium hydroxide, in the following ratio of components, g / l:

Sodium silicate 0.5 Sodium phosphate 2-5 Sodium hydroxide 2-5 Water Up to 1 liter

(US application No. 2009223829)

The plating is carried out in an electrolyte solution containing Nickel sulfate.

The disadvantages of this method are the high complexity and duration of the process of electrochemical treatment of magnesium alloys, the use of nickel compounds in an electrolyte solution requires energy-intensive treatment facilities.

Also known is a method of producing protective coatings on magnesium, aluminum, titanium alloys, including electrochemical treatment with alternating anode-cathode current in an alkaline electrolyte, electrochemical treatment is carried out with alternating current density of 30-70 A / dm ² with a pulse duration and pauses of 100-300 μs, with a ratio of amplitudes of the anode and cathode current of 1.06-2, at an electrolyte temperature of 15-30 ° C (RF patent No. 2046157).

The disadvantages of the known method of coating are reduced protective properties of the coatings, high energy intensity of the process.

The closest analogue taken as a prototype is a method of producing protective coatings on magnesium alloys, including electrochemical treatment with alternating current in an electrolyte solution containing sodium silicate and sodium fluoride, in which the electrochemical treatment is carried out with alternating current, with an increase in voltage value from 0 to 250- 300 V at a speed of 0.25-0.28 V / s and a current density of 0.5-1.0 A / cm ² at anodic polarization, voltage 25-30 V at the cathodic polarization of the product and the ratio of the periods of the anodic and cathodic polarization τ _a / τ _k, avnom 1 for 8-20 min in an electrolyte having the following chemical composition, g / l:

Sodium silicate 12-30 Sodium fluoride 5-10 Water Up to 1 liter

(RF patent 23 5 7016)

The disadvantage of this method is the inability to obtain a uniform thickness and porosity of the coating on parts of complex configuration, while the adhesion of the paint materials to the coating is deteriorated and its anticorrosion properties are reduced. Also, when exposed to fire, a magnesium alloy coating does not provide protection against ignition.

An object of the invention is to develop a method for producing protective coatings on magnesium alloys with increased corrosion resistance and fire resistance.

The stated technical problem is achieved by the fact that the proposed method for producing protective coatings on magnesium alloys, including electrochemical treatment with alternating polarization current in an electrolyte solution containing sodium silicate and water, in which the electrochemical treatment is carried out at a current density of 5-25 A / dm ² and the ratio the amplitudes of the anodic and cathodic polarization voltages U _a / U _k equal to 2-4 in the electrolyte additionally containing alkali metal hydroxide, sodium vanadium and benzol triazole in the next the ratio of components, g / l:

Sodium silicate 5-15 Alkali metal hydroxide 2-12 Sodium Vanadium Acid 0.2-1 Benzotriazole 0.01-0.05 Water Up to 1 liter

It has been established that the introduction of benzotriazole into the proposed method, which forms complex compounds in the process of coating formation, makes it possible to increase corrosion resistance due to their inhibitory effect. Carrying out electrochemical processing at the declared ratios of the amplitudes of the anodic and cathodic polarization voltage U _a / U _k , current density in the presence of vanadium cations in the electrolyte solution allows the formation of a composite heteroxide coating structure that increases fire resistance. The introduction of alkali metal hydroxide, for example potassium hydroxide and sodium, allows the use of a current of lower density, which significantly reduces energy consumption in the implementation of the proposed method.

Examples of the method

Example 1

The electrolyte was prepared by sequentially dissolving the starting components with continuous stirring using a mechanical stirrer and holding the prepared solution for 30 minutes. A pre-treated sample of magnesium alloy MA20 with a size of 25 × 15 × 2 mm (anode) was placed in a prepared electrolyte containing, g / l: sodium silicate (Na ₂ SiO ₃ · 5H ₂ O) - 15; sodium hydroxide (NaOH) - 12; sodium vanadium (NaO ₃ V · 2H ₂ O) - 1; benzotriazole (C ₆ H ₅ N ₃ ) - 0.05.

The cooling of the electrolyte during the coating process was carried out using a heat exchanger made in the form of a coil made of glass and cooled with running water.

A stainless steel plate was used as a cathode, the area of which is an order of magnitude larger than the sample being processed.

The sample was subjected to electrochemical treatment at a current density of 5A / dm ² , the ratio of the anodic and cathodic polarization voltage U _a / U _k equal to 4, washed and dried. The study of the protective properties of the obtained coating on magnesium alloy MA20 was carried out in a salt spray chamber Votsch VSC-1000 in accordance with GOST9.905, GOST9.308. Coating thickness was measured using a MiniTest 2100 portable electronic thickness gauge.

To study flammability, coated metal samples were exposed to a Bunsen burner flame with a nozzle having a nominal internal diameter of 9.5 mm and a flame height of 38 mm, and the flame temperature in its center was 800-850 ° C (Aviation Rules Part 25. Airworthiness Standards transport category. International Aviation Committee. 2004).

Examples 2, 3 were carried out analogously to example 1.

Example 4 was carried out according to the prototype method. The electrolyte was prepared by sequentially dissolving the starting components with continuous stirring using a mechanical stirrer and holding the prepared solution for 30 minutes. A pre-treated sample of magnesium alloy MA14 with a size of 30 × 5 × 1 mm (anode) was placed in a prepared electrolyte containing, g / l: sodium silicate (Na ₂ SiO ₃ · 5H ₂ O) - 30; sodium fluoride (NaF) - 10.

The cooling of the electrolyte during the coating process was carried out using a heat exchanger made in the form of a coil made of glass and cooled with running water.

A stainless steel plate, the area of which is an order of magnitude larger than the sample being processed, was used as a cathode.

The sample was subjected to electrochemical treatment with alternating current, with increasing voltage from 0 to 250-300 V at a speed of 0.25-0.28 V / s and a current density of 0.78 A / cm ² = 78 A / dm ² at anodic polarization voltage 25-30 V at the cathodic polarization of the product and the ratio of the periods of the anodic and cathodic polarization τ _a / τ _k equal to 1 for 15 minutes

The study of coating thickness, fire resistance and corrosion resistance was carried out analogously to example 1.

The composition of electrolytes, process parameters and properties of the resulting coatings are shown in the table.

From the analysis of the table it is seen that the corrosion resistance of the coating according to the proposed method is 1.8-2 times higher than the coating according to the prototype method. The fire resistance of the coating according to the proposed method is 1.7 times higher than the coating according to the prototype method.

Application of the proposed method will allow the use of products from wrought and cast magnesium alloys of a wide range in all climatic conditions, and will reduce the energy consumption of the coating formation process.

Claims (1)

A method of producing protective coatings on magnesium alloys, including electrochemical treatment with alternating polarization current in an electrolyte solution containing sodium silicate and water, characterized in that the electrochemical treatment is carried out at a current density of 5-25 A / dm ² and the ratio of the amplitudes of the anode and cathode polarization voltage U _a / U _k equal to 2-4 in an electrolyte additionally containing alkali metal hydroxide, sodium vanadium and benzotriazole in the following ratio of components, g / l:
sodium silicate 5-15 alkali metal hydroxide 2-12 sodium vanadium 0.2-1 benzotriazole 0.01-0.05 water up to 1 l