RU2241074C1 - Method for electrolytic deposition of iron/manganese/ phosphorus alloy - Google Patents

Abstract

FIELD: electrolytic processes.

SUBSTANCE: invention relates to electrolytic deposition of solid wear-resistant coatings employed for restoration and strengthening of surfaces of parts. Method of invention comprises deposition of coating from electrolyte containing, kg/m³: manganese dichloride 5-10, ferrous chloride 300-450, sodium hypophosphite 2-15, and aqueous hydrochloric acid 0.5-1.5 with alternate asymmetric current with asymmetry coefficient 1.2-6, cathodic current density 30-60 a/dm², electrolyte temperature 20-40^oC, and pH 08.

EFFECT: lowered electrolyte temperature, increased productivity, coating-to-substrate adhesion, microhardness, and wear resistance.

Description

The invention relates to the field of electrolytic deposition of hard, wear-resistant coatings, in particular iron-manganese-phosphorus 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 M.P. 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 alloy of iron-manganese-phosphorus from an electrolyte containing: manganese chloride, iron chloride, sodium hypophosphite, hydrochloric acid. The process is conducted with direct current at a temperature of 50-70 ° C and a cathode current density of 5-60 A / dm ² (Petrov Yu.N., Sidelnikov V.K., Yagubets A.N. Study of the wear resistance of electrolytic alloys of iron with phosphorus. / / Tr. KSHI, vol. 87. - Chisinau, 1972. - S.60-67).

The disadvantage of this method is the limited microhardness of the coating, low adhesion of the coating to the base, low deposition rate of the coating and the use of high electrolyte temperatures.

To eliminate the above disadvantages, a method of electrolytic deposition of an alloy of iron-manganese-phosphorus, which has high productivity due to the use of an alternating asymmetric current, is proposed. 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: manganese (II) chloride, iron chloride (II), sodium hypophosphite, hydrochloric acid in the following ratio of components, kg / m ³ :

Manganese (II) chloride 5-100

Iron chloride (II) 300-450

Sodium hypophosphite 2-15

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 cathodic current densities of 35-40 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, sodium hypophosphite and manganese chloride.

Manganese chloride is in the range of 5-100 kg / m ³ . The lower limit is due to the fact that when the content is less than 5 kg / m ³ manganese chloride, there is no noticeable change in the physical and mechanical properties of the coating. The upper limit is limited to a manganese chloride content of 100 kg / m ³ . When the content is more than 100 kg / m ³ there is an intensive formation of manganese 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 A.V. 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.

Sodium hypophosphite is in the range of 2-15 kg / m ³ . The lower limit is due to the fact that when the content is less than 2 kg / m ^{3 of} sodium hypophosphite, there is no noticeable change in the physical and mechanical properties of the coating. The upper limit is limited by the content of sodium hypophosphite 15 kg / m ³ . When the content is more than 15 kg / m ³ there is an intensive formation of phosphorus 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 economically unprofitable. 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 30-60 A / dm ² . Below 30 A / dm ² the current density is impractical to use, because The electrolysis process has a low coating deposition rate. At a cathodic current density above 60 A / dm ² , strong dendritic formation occurs and the current efficiency decreases sharply.

The beginning of coating deposition occurs starting from the asymmetry coefficient β = 1.2, which provides a high adhesion of the coating to the substrate, Gcc = 300 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 direct current. 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 an alloy of iron-manganese-phosphorus are the conditions given in the example:

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

Manganese (II) Chloride 50

Iron chloride (II) 350

Sodium Hypophosphite 8

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 at β = 1.2 and is gradually increased to β = 5 over 3-5 minutes. The coating has Gst = 300 MPa, microhardness Нμ = 8400 MPa, deposition rate of 0.3 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 alloy of iron-manganese-phosphorus from an electrolyte containing manganese (II) chloride, iron chloride (II), sodium hypophosphite, hydrochloric acid, characterized in that the deposition is from an electrolyte consisting of, kg / m ³ : Manganese (II) chloride 5-100 Iron chloride (II) 300-450 Sodium hypophosphite 2-15 Hydrochloric acid 0.5-1.5 on alternating asymmetric current with an asymmetry coefficient of 1.2-6 at a cathodic current density of 30-60 A / dm ² , an electrolyte temperature of 20-40 ° C, an electrolyte acidity of pH 0.8.