SU1708941A1 - Method for electrochemical aluminizing - Google Patents

Abstract

The invention can be used in the manufacture of a mold for casting under pressure, molds. The purpose of the invention is to increase the heat resistance of the coating and reduce costs. This is ensured by the deposition of an aluminum sheet by deposition from a molten salt. Deposition is carried out using graphite anodes at a current density of 0.05-2.5 A / cm ^, a temperature of 700-850 ° C for 2-10 minutes in the following ratio, wt.%: Sodium fluoride 29-32; sodium chloride 15--18, aluminum fluoride else. Table 1 of the invention. The invention relates to foundry, in particular, to the manufacture of molding parts, and can be used in the manufacture of molds > & for die casting, molds. One of the ways to obtain the most accurate blanks in mechanical engineering is injection molding. The stability of the forming parts attach great importance. The destruction of the shaping parts starts from the working surface, as it is subjected to cyclical exposure to high temperatures, the effects of deformations, stresses and chemical interaction with the liquid metal. During operation, thermal fatigue, irreversible shaping and wear occur on the working surface of the forming parts, resulting in their exit from the construction .. Improving the durability of the forming parts can be achieved by proper selection of the material. For these purposes, expensive chrome-and-phravanized and chrome-molybdenum-iadium steels, alloys based on refractory metals are used. The application of protective coatings on the forming parts also increases their durability. A known method for the manufacture of forming parts involves the manufacture of parts from steel ZH2V8F and subsequent electrolytic chrome plating. under the action of a jet of liquid metal, the coating from the working surface of the forming parts is destroyed. The disadvantages include poor wettability with oils and lubricants, low plasticity. C ^ VI о00оJSI ^

Description

The closest in technical matter and the effect achieved is the method of melt salt aluminization, containing,%: NaCI 35; NaF 15; KCI 35; A1Pz 15 at a current density of 0.3 A / cm, a temperature of 800 ° C for 10-15 minutes. Metallic aluminum is used as a soluble anode, the product being mounted on a molybdenum suspension serves as a cathode.

The disadvantages of this method include the insufficient thickness of the aluminum coating and, consequently, the low resistance of aluminized parts. In addition, aluminum at a process temperature of 800 ° C is in the molten state (aluminum melting point is 660 ° C), which constructively complicates the current lead to the molten anode.

The aim of the invention is to increase the heat resistance of the coating and reduce costs.

The goal is achieved by the fact that in the method of electrochemical aluminization, mainly formative steel parts, including the deposition of a coating from a melt of sodium fluoride, aluminum and sodium chloride, precipitation is carried out using graphite anols at a current density of 0.05-2.5 A / cm, temperature 700-850 ° C, for 210 minutes, in the following ratio, wt.%: Sodium fluoride 29-32; sodium chloride 15-18; fluoride al | ini rest.

The method is designed mainly for shaping parts.

The method is carried out as follows.

The billet is made from a series of steel grades of the type 3.40X, after which it is machined to obtain the desired configuration, heat treatment and grinding. The choice of the mode of heat treatment of parts depends on the design of the molds, its size, wall thickness, material used for the manufacture of castings and other factors. Quenching and tempering are most commonly used. The reinforcement coating is applied by electrolytic aluminization in the molten salt. For aluminiumization in air, an electrolyte is taken, containing 29-32% NaF, 15-16% NaCI, the rest A1F3. Aluminization is carried out for 2-10 minutes at a current density of 0.05-2.5 A / cm and a temperature of 700-850C. The cathode is a shaping part.

and graphite is used as anodes. electrodes.

The method was implemented under industrial conditions. Tests conducted on

die for casting body DN-15. The die blank made of steel 40X, after machining, was subjected to heat treatment, consisting of quenching at 980 ° C. After heat treatment, the hardness was 40-45 HRX. A molten salt for electrolysis was prepared in a three-phase electric furnace with graphite electrodes. After melting the components of the electrolyte in the melt introduced

aluminum in the amount of 100 g and then the matrix, which is the cathode, was placed into the melt-averaged composition.

The process was conducted at 700-850 ° C, current density of 0.05-2.5 A / cm for 2.10 and 20 min

(see tab.).

Experiments were also carried out on the deposition of a coating from molten salts in a known manner on parts made of 40X steel and ZHZMZF steel. During operation

The failure of molds mainly consists in the appearance of a high-angle mesh and cracks during casting. Therefore, in all the experimental studies on the durability of molds, not durability is practically determined, but

heat resistance. The existing various criteria and indicators for estimating the heat resistance of materials are not applicable when calculating the heat resistance of forming parts. Therefore, the heat resistance of aluminized parts was determined experimentally by the number of cycles of heat cycles before the occurrence of a defect.

With high temperature aluminization, i.e. at temperatures above the melting point of aluminum, increases

diffusion rate of aluminum atoms in the alloy. Aluminum forms a solid solution with iron over a wide range of temperatures and concentrations. Increasing the aluminum content leads to the formation of intermetallic compounds. The strength of the coating depends on the size of the diffusion layer, the microhardness of which is 644-713 kg / mm. Offered

electrolysis modes provide optimal thickness of the diffusion layer.

To obtain a coating with a thickness of 0.032-0.5 mm, the electrolysis process is sufficient to lead at 700-850 ° C. At temperatures below 700 ° C, the electrolyte has a high viscosity and low electrical conductivity. An increase in temperature above 850 ° C is associated with high power consumption, as well as with the release of fluoride into the environment.

exceeding permissible sanitary standards.

The current density of 0.05 A / cm does not allow to obtain a coating of sufficient thickness and continuity. At a current density above 2.5 A / cm, the rate of the electrochemical reaction of the ion discharge is higher than the rate of diffusion of ions into the metal, which leads to a decrease in the thickness of the diffusion coating.

The time of the electrolysis process is determined by the required thickness of the reinforcement coating. In order to obtain the minimum thickness of the coating, which is a diffusion layer and which ensures an increase in the thermal resistance of the product, the treatment must be carried out for at least 2 minutes.

The optimal process time is 2-10 min. / A further increase in the duration of the process is not accompanied by a significant increase in the protective layer and, accordingly, an increase in the heat resistance of the working surface of the product, in addition, such a coating is characterized by a considerable heterogeneity in thickness.

The optimal electrolyte composition is: 29-32% NaF, 15-18% NaCI, the rest, A1P3. A change in the content of electrolysis components leads to an increase in the viscosity of the melt with precipitation of solids and a decrease in electrical conductivity. Conducted tests have shown that the application of an aluminum coating makes it possible to increase the heat resistance of the matrix. Steel matrix 40X, electrolytic aluminized. maintains 800012000 pressings of brass.

The heat resistance of parts made by the inventive method is doubled, as a result of which, in order to produce castings of brass on machines, pressure casting requires less than two special tools in two times. Forming parts due to the aluminized layer with a depth of 0.3-0.6 mm can be made from a variety of steel grades, for example 40X, the cost of which is five times lower than the traditionally used steel ZHZMZF.

Formula a and 3 for brea

A method of electrochemical aluminization, predominantly forming steel parts, including the deposition of a coating from molten sodium fluoride, aluminum and sodium chloride, characterized in that, in order to increase the heat resistance of the coating and reduce costs, the deposition leads to current densities of 0.05-2.5 A / cm , temperature 700-850 ° C for 2-10 minutes with the following ratio of components, wt.%: sodium fluoride 29-32: sodium chloride 15-18: aluminum fluoride the rest.

Claims (2)

Claim The method of electrochemical aluminization, mainly of forming steel parts, including the deposition of a coating from a melt of sodium fluorides, aluminum and sodium chloride, characterized in that, in order to increase the heat resistance of the coating and reduce costs, the deposition is carried out at a current density of 0.05-2, 5 A / cm ² , temperature 700-850 ° C for 2-10 min in the following ratio of components, wt.%: Sodium fluoride 29-32: sodium chloride 15-18; aluminum fluoride rest. Electrolyte Composition 29.0 15.0 Si.O 30.5 16.5 53.0 30.5 "6.5 53.0 32,0 18.0 50,0 18.0 50,0 ί Temperature, • s Current density, A / cm ¹ Electrolysis time, min Coating thickness mm Heat resistance of aluminized parts (number of fittings ^ 700 0.05 20 0.66 11500 »0 0.61 11000 2 0,032 6500 2,5 20 0.55 12000 10 · 0.68 12000 2 0.0166 6000 850 0.05 20 0.60 12100 10 0.65 11700 2 0.016 . 6800 2,5 20 0.65 .11500 »0 0.63 11500 2 0.012 6200 700 0.05 20 0.62 11000 10 0.60 11200. 2 0.017 6300 2,5 20 0.67 .11600 to 0.60 11500 2 0.018 6100 850 0.05 20 0.69 12000 10 0.58 11800 2. 0.010 6600 2,5 20 0.72, 11700 10 0.68 . 11500 2 0,021 6200 700 0.05 20 0.30 9600 10 0.35 9500 2 0.06 7500 2,5 20 0.65 * 11800 »0 0.62 11500 2 0,021 6000 850 0.05 20 0.65 12000 10 0.50 11800 2 0.0188 : bbo about 1,5 20 0.62 12000 »0 0.51 11900 2 0.019 6700 . 700 Note Norm of thermostats' bones of a shape-forming * zuyutsik of details when molding under pressure to a plate ** no 5000 aapres ** soyeok 28.0 "*, 0 58.0 3 *, about 29.0 19.0 "5.0 67.0 56.0 700 700 Process is not going 0.06 The electrolyte is a deuffaeyau system. The solid phase covers the thick surface of the surface. Current drops to near zero in a matter of seconds That in "5.0" 5.0 2.6 Known (steel ZHZNZF) 35.0 800 0.3 0.3 20 0.08 5000 10 0.0012 6800 2 Coverage discrete 20 0,07 5000 10 0.0016 6900 2 Discrete coating 6900 Yu 0.08 6700 fifteen 0.012 5200