RU2263727C2 - Method for electrolytic deposition of iron-aluminum alloy - Google Patents

Abstract

FIELD: electrolytic deposition of hard wear-resistant coatings, in particular, iron-aluminum coatings used for recovering and reinforcement of part surfaces.

SUBSTANCE: method involves providing deposition from electrolyte containing, kg/m³: aluminum chloride 50-600; iron chloride (II) 200-700; potassium (sodium) chloride 80-100; hydrochloric acid 0.5-1.5, with asymmetrical alternate current having asymmetry coefficient of 1.2-6, cathode current density of 30-70 A/dm², electrolyte temperature of 20-40 C, pH of electrolyte of 0.8.

EFFECT: increased efficiency, improved adhesion of coating with base, increased micro hardness and wear-resistance.

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Description

The invention relates to the field of electrolytic deposition of hard, wear-resistant coatings, in particular iron-aluminum coatings used to restore and harden the surfaces of parts.

A known method of electrolytic deposition from ferrous chloride electrolyte containing 200-250 kg / m ^{3 of} ferric chloride and 2-3 kg / m ^{3 of} hydrochloric acid (Melkov MP Solid cooling of automotive parts. M., "Transport", 1971, p . 19-20). However, this electrolyte operates at a high temperature (60-80 ° C) and provides coatings with a microhardness value of 4500-6500 MPa.

The prototype is a known method of electrolytic deposition of an iron-aluminum alloy from an electrolyte containing: aluminum chloride, iron chloride, potassium chloride (sodium), hydrochloric acid, glycerin. The process is carried out with direct current at a temperature of 20-100 ° C and a cathode current density of 5-100 A / dm ² (A.S. No. 377432, IPC C 23 b 5/32. Method of electrolytic deposition of an iron-aluminum alloy). The disadvantage of this method is the limited microhardness of the coating, low adhesion of the coating to the base, low coating deposition rate and the use of high electrolyte temperatures, low wear resistance.

To eliminate the above disadvantages, a method for electrolytic deposition of an iron-aluminum alloy is proposed, which has high productivity due to the use of an alternating asymmetric current. It is cost effective because deposition occurs at high cathodic current densities and low electrolyte temperatures, which ensures a high deposition rate of coatings. The resulting coatings have high adhesion to the base, high microhardness and wear resistance. Precipitation occurs from an electrolyte containing aluminum chloride, iron chloride (II), potassium chloride (sodium), hydrochloric acid in the following ratio of components, kg / m ³ :

aluminum chloride 50-600 iron chloride (II) 200-700 potassium chloride (sodium) 80-100 hydrochloric acid 0.5-1.5

The electrolysis is carried out at a temperature of 20-40 ° C with an alternating asymmetric current with an interval of cathode current densities of 30-70 A / dm ² and an asymmetry coefficient β = 1.2-6. The acidity of the electrolyte is in the range of pH 0.8.

The electrolyte is obtained by combining an aqueous solution of ferric chloride, aluminum chloride and potassium chloride (sodium).

Aluminum chloride is in the range of 50-600 kg / m ³ . The lower limit is due to the fact that when the content of less than 50 kg / m ³ aluminum chloride, there is no noticeable change in the physico-mechanical properties of the coating. The upper limit is limited to an aluminum chloride content of 600 kg / m ³ . When the content is more than 600 kg / m ³ there is an intensive formation of aluminum oxides, which sharply reduces the physical and mechanical properties of the electrolytic coating.

The concentration of ferric chloride is in the range of 300-450 kg / m ³ . The lower limit indicates the zone of minimum viscosity. The upper limit shows the zone of maximum electrical conductivity (Shvetsov AN Fundamentals of the restoration of parts by ostalivanie. Omsk, 1973, p.77-79).

The content of hydrochloric acid is in the range of 0.5-1.5 kg / m ³ . The upper limit is set for economic reasons, the electrodeposition of iron at the cathode occurs with the simultaneous discharge of hydrogen. With an increase in the content of hydrochloric acid, the amount of discharging hydrogen sharply increases and the current efficiency decreases. The lower limit is selected according to the qualitative characteristics of the structures of electrolytic iron. When the content of hydrochloric acid is less than 0.5 kg / m ³ there is a strong alkalization of the cathode layer. Hydroxide formed in the near-cathode layer is included in the coating and this worsens their structure.

Potassium chloride (sodium) is in the range of 80-100 kg / m ³ . The lower limit is due to the fact that when the content is less than 80 kg / m ³ potassium chloride (sodium), there is no noticeable change in the physico-mechanical properties of the coating. The upper limit is limited by the content of potassium chloride (sodium) of 100 kg / m ³ . When the content is more than 100 kg / m ³ there is an intensive formation of potassium (sodium) oxides, which sharply reduces the physical and mechanical properties of the electrolytic coating.

The temperature range is in the range of 20-40 ° C. The lower limit is limited by the diffusion properties of the electrolyte. The ion motion is slow and the deposition rate of the coating is low. Above 40 ° C, the use of electrolyte is unprofitable from an economic point of view. A qualitative change in the coating does not occur, but the cost of heating the electrolyte increases.

The cathodic current density is in the range of 40-80 A / dm ² . Below 40 A / dm ² the current density is not advisable to use, because The electrolysis process has a low coating deposition rate. At a cathodic current density above 80 A / dm ² , strong dendritic formation occurs and the current efficiency decreases sharply.

The beginning of coating deposition takes place with an asymmetry coefficient β = 1.2, which provides high adhesion of the coating to the substrate, Gst = 350 MPa. If the asymmetry coefficient is lower than 1.2, precipitation does not occur. In the process of electrodeposition, the asymmetry coefficient is gradually increased to β = 6, which is characterized by a high and stable deposition rate of the coating. A further increase in the asymmetry coefficient is not recommended, because with a further decrease in the anode component, the process switches to a mode close to constant current, and the quality of the coatings deteriorates. Due to the different values of the asymmetry coefficient, it is possible to obtain coatings with various physical and mechanical properties.

Based on the tests, the optimal conditions for the method of electrodeposition of the iron-aluminum alloy are the conditions given in the example:

The electrolyte consists of the following components in quantities, kg / m ³ :

aluminum chloride 350 iron chloride (II) 350 potassium chloride (sodium) 90 hydrochloric acid 1,0

The process of electrolytic deposition of the coating is carried out at a temperature of 40 ° C and a cathodic current density of 40 A / DM ² . The deposition process begins with β = 1.2 and is gradually increased to β = 6 over 3-5 minutes. The coating has Gst = 350 MPa, microhardness Нμ = 8000 MPa, deposition rate of 0.35 mm / h.

The proposed method has high performance due to the use of alternating asymmetric current. It is cost effective because Coating deposition occurs at a high cathodic current density and has a high coating deposition rate. The coatings obtained by the proposed method have high microhardness and wear resistance, which allows them to be used in the national economy for the restoration and hardening of surfaces of machine parts.

Claims (1)

The method of electrolytic deposition of an iron - aluminum alloy from an electrolyte containing aluminum chloride, ferric chloride (II), potassium chloride (sodium), hydrochloric acid, characterized in that the deposition is from an electrolyte containing, kg / m ³ : Aluminum chloride 50-600 Chloride Iron (II) 200-700 Potassium Chloride (Sodium) 80-100 Hydrochloric acid 0.5-1.5 on an alternating asymmetric current with an asymmetry coefficient of 1.2-6, a cathode current density of 30-70 A / dm ² , an electrolyte temperature of 20-40 ° C, an electrolyte acidity of pH 0.8.