RU2489527C2 - Electrolyte composition of antifriction electrolytic zinc-iron alloy for deposition in hydromechanical activation conditions - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: electrolyte contains the following, g/l: zinc sulphate 200-240, iron sulphate 15-20, sodium carbonate 80-120, ammonium sulphate 30, tetraethylammonium hydrochloride 3-4.

EFFECT: high adhesion of the coating to components, electrolyte stability and reduced dendrid formation.

Description

The invention relates to electroplating, in particular to electrolytic deposition of a zinc-iron alloy in order to restore worn surfaces of machine parts, for example, sliding bearings of automobile engines.

Electrolyte solutions for the deposition of zinc-iron alloys are known, containing iron sulfate, zinc sulfate, aluminum sulfate, sodium sulfate, sodium salt of naphthalene disulfo acid, boric and ascorbic acid. However, coatings obtained from these electrolyte compositions have poor adhesion to the base metal. Electrolytes have a weak scattering power, are not efficient enough, and under conditions of alloy precipitation by hydromechanical activation they are subject to oxidation and pollution [1, 2].

The closest technical solution, selected as a prototype, is the known composition of the electrolyte [3] used for the deposition of zinc-iron alloy, containing in g / l:

zinc sulfate 250-300, ferric chloride 60-100, sodium fluoride 10, boric acid 25, primary hydrochloride alkylammonium (C ₆ -C ₁₂ ) 1-2.

This electrolyte was used to restore worn parts from aluminum and iron-carbon alloys at temperatures of 20-30 ° C, a cathode current density of 40-60 A / dm ² and an electrolyte flow rate of 1.5 l / s.

Using this method to restore steel products is difficult, since the electrolyte has a complex composition, it is difficult to adjust the composition in the process.

Precipitation has a coarse-grained structure, low adhesion to the base and, when recovering steel parts, have a high specific temperature coefficient of linear expansion. The electrolyte is prone to oxidation, since chlorine and fluoride are released during the electrolysis of iron chloride and sodium fluoride. The primary alkylammonium hydrochloride used for flotation is a mixture of RNH ₂ NCl, where R = C ₆ H ₁₃ -C ₁₂ H ₂₅ does not always have a reproducible composition.

In addition, the electrolyte is prone to dendride formation at high current densities and is inefficient under unsteady conditions of alloy deposition.

The objective of the invention is to increase the physico-mechanical characteristics of the coating: adhesion, improve the structure of the precipitate, the chemical resistance of the solution and reduce dendrite formation.

The essence of the invention is as follows: a highly effective composition of antifriction electrolytic zinc-iron alloy for deposition under conditions of hydromechanical activation is proposed. It contains zinc sulfate, iron salt, sodium salt and an organic additive. In this case, iron sulfate was used as the iron salt, sodium carbonate was used as the sodium salt, and tetraethylammonium hydroxide was used as the organic additive in the following component ratios, g / l:

zinc sulfate 200 ÷ 240 iron sulfate 15 ÷ 20 sodium carbonate 80 ÷ 120 ammonium sulfate thirty tetraethylammonium hydrochloride 3 ÷ 4.

For the preparation of the zinc-iron electrolyte, all components are dissolved in separate containers in distilled water, heated to 60-70 ° C. Then the solutions are filtered and poured into a working bath. The electrolyte should contain as many salts of iron, zinc, sodium carbonate, ammonium sulfate and tetraethylammonium hydrochloride as required by the calculation of the working capacity of the bath. After this, add water to the mark corresponding to the upper level of the electrolyte. Check the pH value, work out for 8-10 hours at a current density of 0.8 ÷ 1.5 A / dm ² with steel cathodes and then proceed to coating.

Hydromechanical activation of metal deposition is characterized by forced circulation of the electrolyte and rotation of the anode. The flow through the electrolyte solution and the rotation of the anode change the ionic lining of the diffusion layer near the cathode surface and, as a result, the rate of ion diffusion to the cathode surface increases, which provides an increase in productivity by 3-4 times, high uniformity of coating, obtaining a finely dispersed structure and a decrease in residual stresses.

Studies of internal stresses showed that they increase with increasing current density and decrease with increasing electrolyte temperatures and with an increase in the concentration of active salts.

At a high current density, it is significantly distorted, the crystal lattice is compacted, at high temperature, the hydrogenation of precipitation decreases, and if we take a low current density and a high electrolyte temperature, then soft, non-stressed precipitates can be obtained.

The adhesion strength for various electrolytes and bath operating conditions varied from 3000 to 12000 N / cm ² . The highest values of adhesion were shown on steel samples, the coating of which was carried out in the baths of the claimed electrolyte. The addition of sodium, ammonium, tetraethylammonium hydrochloride salts to the bath increased the adhesion of the precipitate to the base, the production of a densified crystal lattice, a decrease in the annoying precipitate, and soft, non-stressed sediments.

The deposition mode of the alloy "zinc-iron": temperature 20-25 ° C, cathodic current density 30-35 A / DM ² , pH = 2.0-2.5, the anode is zinc (soluble).

The claimed composition of the electrolyte is characterized by a decrease in the concentration of active salts, since with an increase in their concentration, the permissible current density can be significantly increased. This leads to the formation of a coarse-grained structure of zinc-iron precipitation with reduced mechanical properties.

The zinc-iron precipitate is deposited on the product at a lower cathodic current density of 30-35 A / dm ² compared to the known cathodic current density of 40-60 A / dm ² , since with increasing current density the hardness of the precipitate increases, its internal voltage. The coatings crack, growths form at the edges of the parts, and with a further increase in the current density, the coating is amorphous, powdery with low adhesion to the parts.

The use of fluorine and chlorine anions in the salts included in the electrolyte, as well as the use of sodium carbonate, can reduce the electrolyte aggressiveness and eliminate corrosion of steel products.

Simplification of the electrolyte composition is also achieved by using tetraethylammonium hydrochloride (C ₆ H ₁₂ NCl) as an organic additive, which is readily soluble in water, has a constant composition and does not change during electrolysis.

Thus, the proposed composition of the electrolyte differs from the known one in that it is simpler in content, productive and meets the technological process when restoring bearing parts under non-stationary conditions (flowing, on various forms of current). Coatings are smooth, dense with a finely dispersed structure, with increased wear and corrosion resistance.

Deposition is carried out in the form of solid alloys of the replacement of zinc ions by iron ions, which ensures the physicomechanical characteristics of the precipitate, which are identical to the characteristics of a stainless steel bearing base, and increases the stability of the electrolyte.

INFORMATION SOURCES

1. USSR author's certificate No. 755897, class C25D 3/56, 1980.

2. USSR author's certificate No. 374383, class C25D 3/56, 1973

3. Patent RU No. 2086712, GOIM 17/06, 08/10/1997 - prototype.

Claims (1)

The electrolyte composition of the antifriction zinc-iron electrolytic alloy for precipitation under hydromechanical activation conditions, containing zinc sulfate, iron salt, sodium salt and an organic additive, characterized in that it contains ammonium sulfate, iron sulfate as iron salt, and sodium salt as sodium carbonate, and as an organic additive - tetraethylammonium hydrochloride, in the following ratio of components, g / l:
zinc sulfate 200-240 iron sulfate 15-20 sodium carbonate 80-120 ammonium sulfate thirty tetraethylammonium hydrochloride 3-4