RU2219027C2 - Method for non-detachable joining of two bodies of different type metals and non-detachable joint made by such method - Google Patents

Abstract

FIELD: methods for joining different type metals, possibly at making assembled units of articles used in instrument making, aircraft manufacture, spatial and missile technologies, in transport, communication, electronics, electrical engineering and other industry branches. SUBSTANCE: method for joining two bodies of different type metals comprises steps of applying onto surface at least of one body coating of metal capable for forming eutectics and intermetallide with one of different type metals having less melting temperature; applying coating with thickness sufficient for forming gradient composite at complete transition of metal of coating into gradient composite; realizing heating and compression in conditions providing complete transition of metal of coating into gradient composite. Non-detachable joint includes two bodies of different type metals and diffusion joining zone in the form of gradient composite including eutectics and at least one intermetallide. EFFECT: possibility for preventing brittle destruction of joining zone, especially at long-term cyclic loads. 16 cl, 8 dwg, 4 ex

Description

 The invention relates to metallurgy and mechanical engineering, and more specifically to methods of joining dissimilar metals, and can find application in the production of assembly units of products used in instrumentation, aviation, space and rocket technology, transport, communications, electronics, electrical engineering and other fields.

 There are numerous methods for joining dissimilar metals. These include, in particular, welding, incl. diffusion, and soldering. In the latter, fusible plastic solders are used to connect the bodies, the strength of which does not exceed the strength of the materials of the bodies to be joined.

 Diffusion welding is one of the varieties of pressure welding. In the diffusion welding of metals in the solid state, a monolithic compound is obtained due to the formation of bonds at the atomic level, which appear as a result of the contact surfaces coming together in the process of local plastic deformation, as a rule, at an elevated temperature, which ensures mutual diffusion in the surface layers of the materials being joined.

 There are various options for joining dissimilar metals by diffusion welding.

So, in accordance with the decision on patent RU 2091200, В 23 К 20/04 dated 06/23/93 a multilayer product of the sleeve type is made in the following sequence of technological operations:
- assembly of the core with the outer and inner shells;
- calibration of the prefabricated workpiece simultaneously on the outer and inner surfaces with thinning the walls of the shells;
- rolling and welding of the open ends of the workpiece;
- thermal diffusion treatment;
- deformation of the workpiece by sequential calibration of its outer and inner surfaces without thinning the walls of the shells.

 In accordance with application 0376248 EPO C 23 C 26/00, F 28 F 19/06, the part for the heat exchanger fins is made in the form of a strip of copper or a copper alloy with a diffusion layer of copper and zinc on one side, another diffusion layer is located on top of this layer a layer of copper, zinc and an element with a lower diffusion coefficient in copper than in zinc. As a result of mass transfer between the joined surfaces, a qualitatively new transition layer is formed in the process of the disappearance of the interface and recrystallization of the structure in this place.

 It should be noted that with such a combination of dissimilar metals, intermediate structural components appear, which, as a rule, worsen the quality of the starting metals in the welding zone if eutectics or intermetallics are formed. Sometimes, these changes in the zone of formation of the welded joint proceed very slowly due to the presence of oxides or low diffusion mobility of metal atoms of the joined bodies or are accompanied by the appearance of significant residual stresses, as a rule, worsening the performance of welded joints.

 To eliminate such undesirable phenomena, intermediate materials of various functional purposes are used.

 A known method of joining dissimilar metals using a damper material that reduces the thermal stresses that occur when welding metals with different temperature coefficients of linear expansion ("Theory, technology and equipment of diffusion welding." Under the general editorship of Doctor of Technical Sciences VA Bachin . - M.: Mechanical Engineering, 1991, p. 150). This method is the closest to the claimed technical essence and is selected by the authors as a prototype.

 According to this method, a compound of aluminum and steel is obtained using intermediate coatings applied to steel parts by galvanic or chemical means, by vacuum deposition, or by other methods. The coating of zinc, silver, copper, nickel, according to the authors of the book, prevents or slows down the formation of intermetallic compounds.

Aluminum or aluminum alloy AMts is connected to steel grades 30, St3, St15 or armco iron through a nickel coating, which is applied to a steel part through a copper sublayer. Welding in vacuum with a vacuum of 10 ^-1 Pa at T = 823K, p = 12 ÷ 15 MPa, t = 2 min can, according to the authors of this source, ensure equal strength of the connection with aluminum and the alloy AMts, respectively. However, there is no direct evidence of such a statement, and in practice, even if equal strength is achieved, then only in the conditions of short-term tensile, shear, and torsion tests.

 In addition, the process of joining dissimilar metals under consideration requires very complex and expensive equipment, including loading, heating and vacuum systems. This greatly complicates the technology, as a result, the nomenclature of units (assembly units) is substantially narrowed, for the manufacture of which this method can be implemented. In essence, it provides the manufacture of parts of only the simplest configuration: flat plates, cylinders of the correct form, and similar products with close cross-sectional sizes.

 A common drawback of known solutions, including of the prototype, is the unreliability in the operation of one-piece bodies made by combining dissimilar metals under long-term exposure to alternating cyclic loads. Products are destroyed especially often in the connection zone due to the formation of low-strength or brittle phases in the form of continuous layers.

 The objective of the invention is the creation of a technology for the production of permanent joints for products made of dissimilar metals having a significant resource and reliability during operation, mainly under prolonged exposure to alternating loads, due to the controlled exclusion of brittle and low-strength layers in the diffusion zone.

 The objective of the invention is to reduce the cost and simplify the technology of manufacturing one-piece products from dissimilar metals while increasing labor productivity by eliminating the need to use equipment that requires complex systems for monitoring the environment, evacuation, heating and loading.

 The technical result of the invention is to ensure the strength characteristics of the connection zone to a level not less than the level of the least durable of dissimilar metals, while maintaining the ductility of this zone.

 The technical result is achieved by the fact that in the method of manufacturing a permanent connection of two bodies made of dissimilar metals, including applying a metal coating to the surface of at least one of the bodies, contacting, heating and hot compression, the coating is applied from a metal capable of forming a eutectic and at least one intermetallic compound with at least one of dissimilar metals that has a lower melting point, the coating being applied with a thickness sufficient to form a gradient ntnogo composite coating with complete transition metal in the gradient composite, the heating and compression is performed in conditions that ensure complete transfer of the coating metal in the composite gradient, and the gradient composite formation process control.

 The specified control consists in the targeted production of a gradient composite of a given chemical and phase composition with a sufficiently high level of plasticity and is based on the results of studies conducted by the authors, which allow us to establish the optimal distribution pattern of eutectic and intermetallic phases in the compound zone (diffusion zone).

 The permanent connection made by the proposed method includes two bodies made of dissimilar metals, and the diffusion zone of the connection made in the form of a gradient composite comprising eutectic and at least one intermetallic compound formed by an additional metal and at least one metal of one from bodies that have a lower melting point, while the content of each of dissimilar metals varies across the width of the connection zone towards each other within 0-100 wt.%, the content of additional metal varies in band width in the range from 0 to a maximum value in the middle area, the hardness of zone maintains constancy of the width of the deviation is not more than 25% from the mean value, and in the case of permanent connection fracture has fracture ductile character.

 A gradient composite is a material of variable composition in the volume of the transition zone, which is thermodiffusively formed from dissimilar metals of the joined bodies and the metal of the intermediate coating. The composite is synthesized from a matrix - a eutectic obtained from the coating metal and, at least, from the metals of the bodies, which has a lower melting point. Elements of contacted metals (alloys) and intermetallic compounds of variable composition are diffusely distributed in the matrix according to the corresponding state diagrams. Intermetallics perform the function of hardening phases. Only the presence of such a rather peculiar and complex structure and composition of the composite provides a favorable combination of strength and ductility, since continuous layers of brittle in nature intermetallic compounds or in pure form of eutectic components, which are characterized by lower values of the melting temperature and strength, are excluded. In the presence of the specified gradient composite, the destruction of the permanent connection of two bodies is plastic.

 According to the claimed method, heating and hot compression is carried out in air or in an inert atmosphere, which, in combination with specific modes and a sequence of stages of the process, provides an inextricable connection of bodies of two dissimilar metals with a connection zone including an additional metal and having strength characteristics not lower than less durable of dissimilar metals.

 Various modes and variants of the sequence of operations are possible, allowing to solve the task.

So, in order to ensure a more tight contact of rough surfaces, in some cases it is advisable to perform heating in 2 stages. First, preliminary heating to a temperature not exceeding 0.5 of the temperature of formation of the lowest melting eutectic, and then to a temperature not exceeding 10-50 ^o With the temperature of formation of the lowest melting eutectic. After heating, compression is carried out.

A process variant is possible when compression is first carried out and then heated to a temperature not exceeding 10-50 ^o C, the temperature of formation of the lowest melting eutectic. This mode is convenient in the case of equipment with high power inertia, for example, a container with gas. When using equipment with less inertia, such as a press that allows you to quickly change the controlled load (force), it is advisable to heat the product to a temperature not exceeding 10-50 ^o With the temperature of formation of the lowest melting eutectic, and then carry out compression.

 The metal coating is applied by any suitable method, for example, by electroplating or chemical deposition or by vacuum ion-plasma spraying. The coating is applied to one of the dissimilar metals before contacting the bodies. It is possible to coat both bodies. In any of these technologies, the total coating thickness should be sufficient for the formation of the gradient composite and the complete transition of the coating metal into the gradient composite.

 Compression is carried out by loading to a predetermined pressure value and holding at the achieved pressure value (force). To create pressure use, for example, a press, a container with gas, a snap made of a material, the temperature coefficient of linear expansion of which is more than the temperature coefficient of linear expansion of each of the dissimilar metals.

 To ensure a controlled process of the formation of a gradient composite, the necessary process parameters are preliminarily selected during the calibration experiment. And then they carry out the process, controlling strict adherence to the found parameters of the modes.

According to the invention, the general conditions for creating an integral connection are as follows:
1) a metal is used as a coating metal, which can form a eutectic and intermetallic compound with at least that of dissimilar metals that has a lower melting point;
2) the heating temperature, exposure time, compression level, coating thickness should be sufficient for the formation of a gradient composite and the complete transition of the coating metal to this composite;
3) metals that are capable of forming eutectics and intermetallic compounds with an additional metal (coating metal) and with each other are used as dissimilar metals.

 With increasing temperature and the duration of exposure to a more than necessary level, continuous layers are formed containing the above phases. This leads to the same disadvantages that were noted above with the known solutions.

 With insufficient heating and a short exposure time, diffusion processes do not have time to go to the right degree (before the formation of the gradient composite) and the connection zone does not have the specified characteristics.

 The choice of optimal process parameters is carried out after studying the structure and properties of the pilot samples obtained under various combinations of the main modes of the proposed method. It is possible to use mathematical modeling and special software.

So, in the process of connecting bodies made of steel and aluminum using a nickel coating, the following modes are preferred:
- t _LOAD = 610-630 ^o C;
- compression at a pressure of at least 10 MPa for 50-150 seconds.

 These modes are suitable both when applying a coating on one of the bodies, and on both bodies.

 In the case of applying a Ni-coating to a steel body when it is connected to a body made of aluminum, the nature of the change in the chemical composition and structure of the diffusion zone is shown in Figs. 1 and 2. The data on the distribution of elements and the type of structure were obtained by X-ray spectral and electron microscopy methods, respectively Kamebaks "and" Mini-SEM ", using a microsection of the cross section of the connection zone.

 Figure 1 shows that the diffusion zone is wider than the applied Ni-coating. The indicated excess in magnitude towards each body depends on the rate of mutual diffusion of Fe, Ni, and Al, i.e. the zone extends to different depths from the contact surface of the connected bodies. The concentration of iron and aluminum varies in the range 0-100 wt.% Towards each other across the width of the diffusion zone; and the Ni content varies over the width of the diffusion zone from 0 (or from the concentration of Ni in steel) to the maximum value in the middle part of the zone. The absence of a 100% Ni interlayer in the zone indicates the transition of Ni to another aggregate state — a gradient composite. 2. The phase heterogeneity and originality of the eutectic type of the matrix structure are illustrated.

 The change in microhardness along the width of the diffusion zone is not pronounced spasmodic with a difference in magnitude of different phase components up to tens of times, as is observed in the known methods of thermodiffusion joining bodies of dissimilar metals. The value of the average microhardness determined by the Vickers method of GOST 9450-76, for example, with the option "steel 09G2S-Ni-Al", was in the range 195-350 MPa. This value of microhardness is characteristic of discontinuous layers consisting of a mixture of phases.

The claimed solution includes two objects - a method and a device connected by a single inventive concept, and is illustrated by the following graphic and photo materials:
FIG. 1 - the nature of the distribution of dissimilar metals and additional metal (coating metal) in the connection zone using the example of steel-Ni-Al;
FIG. 2 - the microstructure of the diffusion zone of an integral connection of 2 ^x bodies of dissimilar metals (steel 09G2S with a nickel coating + Al technical grade) obtained by the claimed method. Magnification 700;
Figure 3 - a cylindrical sample made by the claimed technology;
Figure 4 - the fracture surface of a cylindrical sample, an increase of 50;
FIG. 5 - annular two-layer sample made according to the claimed technology, to failure;
FIG. 6 - ring two-layer sample made according to the claimed technology, after the test;
FIG. 7 - an annular two-layer sample made according to the claimed technology, after low-cycle fatigue tests;
FIG. 8 - annular two-layer sample made according to the claimed technology, after tensile tests in the tangential direction to fracture.

 The following examples characterize the invention.

Example 1. Previously, before starting the manufacturing process of samples, the parameters of the individual stages were determined during the calibration experiment. Then, on the end surfaces of the two cylinders ⌀ = 20 mm and h = 35 mm from 09G2S steel (C≤0.12 wt.%, Mn = 1.3-1.7 wt.%, Si = 0.5-0.8 wt.%) by a method of galvanic deposition according to the method described in GOST 9,305-84, a layer of nickel 3-5 microns thick was applied. Disc ⌀ = 20 mm and h = 5 mm of aluminum mark A99 (Al≤99,9 wt.%) With σ = 60-70 MPa _in the surface of which was subjected to chemical cleaning (etching in alkali + lightening in nitric acid) was placed between steel cylinders, then using a press equipment, an axial compressive force of 6.3 kN was applied to the assembly for 10 seconds, then the force was reduced to 3.15 kN and the entire assembly was heated to a temperature of 600-615 ^o C. After reaching the set temperature the force was increased to 6.3 kN and, at a fixed force and temperature, the assembly was held for 1.5 minutes. The assembly was cooled to room temperature with a residual force of 3.15 kN. Samples for tensile testing were cut from the obtained integral assemblies (Fig. 3), where 1 is steel, 2 is aluminum. The test was carried out on a universal machine HUS 1060 company MFL. The test procedure involved determining the magnitude of the force at which the destruction of the sample occurred. As shown by the tensile tests of the obtained one-piece steel-aluminum-steel joints, the tensile strength of such a compound was 65 MPa, and the fracture surface is wave-like (Figure 4), which indicates the plastic nature of the fracture zone. The average microhardness of the diffusion zone was 280 (260-300) MPa. The deviation from the average value was about 7%. It should be noted that the destruction occurred along a layer of aluminum directly adjacent to the diffusion zone.

Example 2. A calibration experiment was carried out under the conditions of Example 1, after which a nickel layer 5-7 μm thick was applied to the body in the form of a hollow truncated cone made of 09G2S steel by chemical deposition using the method described in GOST 9.305-84. A nickel-coated steel cone was inserted inside an A99 aluminum conical body, the surface of which was previously subjected to dry cleaning (etching in alkali and clarification in nitric acid). Using a press by axial loading, a pressure of 20 MPa was created on the contact surface of the steel and aluminum cones, after holding for 10 seconds, the load was reduced to a level providing a contact pressure of 10 MPa, and the assembly was heated to a temperature of 620 ^o C. After reaching the set temperature, the load was increased to level providing contact pressure of 20 MPa. At a fixed load and temperature, the assembly was held for 1.5 minutes. Next, the assembly was cooled to room temperature under a load providing a contact pressure of 10 MPa. From the obtained one-piece assembly, annular bilayer samples 5 mm thick were cut out (Figure 5). Ring samples were tested for slice on a universal machine HUS 1060 company MFL. The test procedure included the determination of the force at which the destruction of the sample was observed when extruding the inner steel ring. According to the test results, the shear joint resistance was 55 MPa. Moreover, the displacement of the steel ring occurred not along the diffusion zone, but along the adjacent layer of the aluminum ring and was accompanied by a large plastic deformation equal to the initial thickness of the ring sample (Fig.6). After which the test was stopped. Peeling of aluminum along the contact boundary is not fixed. The average microhardness was 258 MPa.

Example 3. A calibration experiment was carried out under the conditions of Example 1, after which ring samples obtained similarly to the samples described in example 2 were subjected to low-cycle fatigue tests according to the method of the applicant on a universal machine HUS 1060 from MFL. The oscillation frequency and amplitude during the tests were 30 Hz and 25 MPa, respectively. The sample withstood 10 ⁴ cycles without failure. (Fig.7). The average microhardness is 350 MPa.

 Example 4. A calibration experiment was carried out under the conditions of Example 1, after which ring samples obtained similarly to the samples described in example 2 were subjected to a tensile test in the tangential direction according to the procedure described in OST 3-3702-84, in order to check the degree of plasticity of the zone contact. The tests were carried out on a testing machine IM-8R. As a result of the experiment, it was found that, in the destroyed samples, Al detachment from steel was observed only in the neck formation zone, and in general, the sample continuity was preserved (Fig. 8). Thus, it was confirmed that during joint deformation of thermally diffusion-bonded layers of steel with Ni-coating and aluminum, the plasticity level of the contact zone is sufficient to maintain the integrity of the joint even in the region of significant deformations. The average microhardness was 202 MPa.

 The results presented in the application indicate a technically reliable and reproducible receipt of integral compounds of dissimilar metals.

 Compared with the known technical solutions, the claimed invention avoids brittle fracture of the joint zone, especially during long cyclic loads, including alternating ones.

 Products made according to the claimed invention can be recommended for operation under conditions of continuously operating for a long time loads, mainly cyclic alternating. When working in these conditions, such compounds provide a high resource and operational reliability.

Claims (16)

1. A method of manufacturing a permanent connection of two bodies made of dissimilar metals, comprising applying a metal coating to the surface of at least one of the bodies, contacting, heating and hot compression, characterized in that the coating is applied from a metal capable of forming a eutectic and, at least one intermetallic compound with at least one of dissimilar metals that has a lower melting point, the coating being applied with a thickness sufficient to form a gradient composite and floor the transition of the coating metal into the gradient composite, heating and compression is carried out under conditions that ensure the complete transition of the coating metal to the gradient composite, and the formation of the gradient composite is controlled. 2. The method according to claim 1, characterized in that the heating and hot compression is carried out in air. 3. The method according to claim 1, characterized in that the heating and hot compression is carried out in an inert atmosphere. 4. The method according to claim 2, characterized in that the heating is carried out in 2 stages — first, preliminary heating is carried out to a temperature not exceeding 0.5 of the formation temperature of the lowest melting eutectic, and then heated to a temperature not exceeding 10-50 ° C the temperature of formation of the lowest melting eutectic, after which compression is carried out. 5. The method according to claim 2, characterized in that the compression is first carried out, and then heated to a temperature not exceeding by 10-50 ° C the temperature of formation of the lowest melting eutectic. 6. The method according to claim 3, characterized in that the heating is carried out to a temperature not exceeding by 10-50 ° C the temperature of formation of the lowest melting eutectic, after which compression is carried out. 7. The method according to any one of claims 1 to 6, characterized in that the coating is applied by galvanic or chemical means or by vacuum ion-plasma spraying. 8. The method according to any one of claims 1 to 7, characterized in that the compression is carried out by loading to a predetermined pressure value with subsequent holding at the achieved pressure, and the pressure is provided either in a press or in a container with gas, or in a snap made of material with a temperature coefficient of linear expansion, the value of which is greater than the values of the temperature coefficients of linear expansion of each of the dissimilar metals. 9. The method according to any one of claims 1 to 8, characterized in that a nickel coating is applied to the body made of steel, after which the specified body is connected to the body made of aluminum. 10. The method according to claim 9, characterized in that the body made of steel is coated with a nickel coating with a thickness of at least 3-5 microns, the bodies are heated to a temperature of 610-630 ° C for 50-150 s, and the compression is carried out at pressure not less than 10 MPa. 11. The method according to any one of claims 1 to 8, characterized in that a nickel coating is applied to the body made of aluminum, and then the specified body is connected to the body made of steel. 12. The method according to claim 11, characterized in that the body made of aluminum is coated with a nickel coating with a thickness of at least 3-5 microns, the bodies are heated to a temperature of 610-630 ° C for 50-150 s, and the compression is carried out at pressure not less than 10 MPa. 13. The method according to any one of claims 1 to 8, characterized in that nickel coatings are applied to the bodies made of aluminum and steel, after which these bodies are connected. 14. The method according to p. 13, characterized in that the total thickness of the nickel coatings is at least 3-5 microns, the bodies are heated to a temperature of 610-630 ° C for 50-150 s, and the compression is carried out at a pressure of at least 10 MPa. 15. One-piece compound, including two bodies made of dissimilar metals and a diffusion zone of the compound adjacent to both one and the second body, containing metals of both bodies and an additional metal, characterized in that it is obtained by the method according to any one of claims 1 -14, while the diffusion zone is made in the form of a gradient composite comprising a eutectic and at least one intermetallic compound formed by an additional metal and at least that metal of one of the bodies that has a lower melting point, soda The holding of each of the dissimilar metals varies across the width of the zone towards each other within 0-100 wt.%, the content of the additional metal varies across the width of the zone from 0 to the maximum value in the middle part of the diffusion zone, the hardness remains constant across the width of the zone with a deviation from the average value is not more than 25%, and when the permanent connection is broken, the kink has a plastic character. 16. The permanent connection according to clause 15, wherein one of the bodies is made of steel, the other is made of aluminum or an aluminum-based alloy, and the diffusion zone of the connection includes a eutectic and at least one intermetallic compound formed by nickel, and at least aluminum, while the content of aluminum and iron varies across the width of the diffusion zone towards each other within 0-100 wt.%, the nickel content varies across the width of the diffusion zone from 0 to the maximum value in the middle of the diffusion zone, hardness anyaet persistence of the diffusion zone width with the deviation not more than 25%, and the strength of the diffusion zone is greater than the strength of aluminum or an aluminum base alloy.

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