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The paper analyzes the results of research of structural features and tensile strength of butt joints of 2 mm thick sheets of structural MA2-1M magnesium alloy produced by nonconsumable electrode argon-arc welding and by friction stir welding. It is shown that in friction stir welding as a result of intensive plastic deformation of the metal, a fine crystalline structure is formed in the welds. It was determined that microhardness of the metal in such a welded joint has minimal values in the zone of thermomechanical impact on the retreating side near the heat-affected zone, where fracture of the specimens occurs during their static tension. Tensile strength of specimens of welded joints produced by friction stir welding, and specimens with root penetration removed to the level of the base material and additionally scraped reinforcement of welds produced by fusion welding, is at the level of 233-236 MPa, which amounts to ~84 % of this value for base material. [ABSTRACT FROM AUTHOR]

The paper gives the results of investigations on vacuum diffusion welding of MA2-1 magnesium alloy. Different technological measures were used in welding: unsupported welding, welding with application of forming matrices, welding without interlayers and with a zinc interlayer. It is found that it is not possible to produce the joint in unsupported welding without an interlayer at 400 ℃ temperature and process duration less than 60 min. Increase of welding temperature or time leads to considerable grain growth. Application of 250 μm zinc interlayer and of the following welding mode: T = 320 ℃, P = 10 mpa, t = 30 min allows producing the joint. analysis of chemical composition in different areas of the joint zone shows that development of diffusion processes in the butt during welding results in pore formation with magnesium content on the level of 17.8-20.12 wt.% in the zinc interlayer at 2-3 μm distance from magnesium/zinc contact line. In the central part of the joint zone the metal chemical composition is close to pure zinc composition. application of forming matrices and an interlayer of zinc in the solid-liquid state in welding in the following mode: T = 340 ℃, P = 10 mpa, t = 30 min. allows producing sound joints due to localisation of plastic deformation in the butt joint. Results of metallographic investigations showed formation in the butt joint of common grains and remains of the interlayer in the form of dispersed particles of 15-50 μm size, with chemical composition of mg-4.53al-0.20mn-63.49Zn, wt.%, having an irregular elongated shape. [ABSTRACT FROM AUTHOR]

The paper presents the results of studies on production of layered composite materials, based on aluminium and titanium alloys, by vacuum diffusion welding, with a broad range of specific weight values, which is achieved due to different layer ratio in each of the composites. Based on a layered composite material, a procedure was proposed for manufacture of three-layer honeycomb panels by vacuum diffusion welding. It is found that the average compressive strength of the three-layer panel with a filler from a layered composite material based on Al-Ti alloys is equal to 47.3 MPa, that is four times higher than the strength of similar honeycomb elements made from an aluminium alloy. It is shown that the layered material has higher thermal stability as compared to aluminium alloys. specimen annealing at the temperature of 700 °C for 30 min does not lead to their early destruction or loss of shape. [ABSTRACT FROM AUTHOR]

Proceeding from the results of literature analysis, the good prospects for application of pressure welding methods, namely diffusion, ultrasonic, and roll bonding, when joining elements from magnesium alloys, are shown. Comparative evaluation of bonding modes was performed. The main directions for producing sound joints were determined. It is shown that the main ways to improve the bonding processes are application of the following approaches: monitoring the temperature-time parameters of bonding, application of interlayers in the form of separate layers from similar materials, based on copper, nickel, zinc or silver, or of eutectic mixtures, butt joint strengthening through application of nano- or finely-dispersed particles, intensification of plastic deformation through superposition of ultrasonic oscillations, increase of plastic deformation intensity, as well as application of heat treatment before and after bonding. [ABSTRACT FROM AUTHOR]

The impact of scandium in filler wires of SvAMg6, Sv1201 and SvAK5 type, as well as arc oscillations, caused by electric current passage through the filler section, on weld structure formation was studied in nonconsumable electrode argon-arc welding of sheet aluminium alloy D16. Curves of metal hardness distribution in the welding zone are shown and strength limits of welded joints and weld metal after natural ageing of the specimens are determined. It is shown that use of scandium filler wires, similar to standard batch-produced ones, leads to formation of a fine-grained dendritic structure of weld metal. However, the subdendritic structure does not form even in welding with arc oscillations, because of a low (0.15-0.17%) scandium content in welds. Use of scandium-containing filler wires can lower the degree of weld metal softening at lowering of the total content of the main alloying elements in them. Positive impact of scandium additives together with application of arc oscillations on the degree of softening and ultimate strength of weld metal is noticeable at application of filler wire of Al-Si alloying system. However, the maximum level of strength, both of the welded joints and the weld metal, is provided in nonconsumable electrode argon-arc welding of D16 alloy 2 mm thick using batch-produced filler wires SvAMg6 and SvAMg63. 21 Ref., 2 Tables, 3 Figures. [ABSTRACT FROM AUTHOR]

The impact of technological measures in vacuum diffusion welding on formation of the structure and mechanical properties of joints of TiAlNb intermetallic alloy was studied in the work. It is shown that welding of intermetallic alloy by the method of vacuum diffusion welding at temperature Tw = 1050 °C, pressure Pw= 10 MPa, for 20 min does not ensure producing sound joints. After welding, the joint line is visible in the butt, along which there is a considerable number of defects in the form of pore lines. Increase of welding parameters up to temperature Tw = 1200 °C, pressure Pw= 30 MPa, welding time of 30 min, as well as application of a ductile interlayer from NbTi alloy 1 mm thick allows improving the conditions of welded joint formation and greatly reducing the number of defects in the butt joint. During welding, common grains and diffusion zone 25-35 µm thick form between the interlayer material and the intermetallic alloy. Application of nanolayered interlayer of Al-Ti system of the total thickness of 25 µm in welding of TiAlNb intermetallic alloy, combined with cyclic loading in the form of 3 cycles of loading-unloading leads to a change of the nature of the structure in the joint zone. In the microstructures of welded joints obtained by optical metallography, the joint line is not visible. Application of electron microscopy allows detecting in the butt joint a diffusion zone 15 to 20 µm thick, close by its chemical composition to that of the intermetallic alloy. Investigation of the compressive strength of welded joints demonstrated that the average strength of joints of TiAlNb intermetallic alloy, produced using an interlayer from NbTi alloy, is equal to 988.2 MPa, and application of a nanolayered interlayer of Al-Ti system in welding allows increasing the average strength of the samples up to 1279.8 MPa. 16 Ref., 2 Tables, 8 Figures. [ABSTRACT FROM AUTHOR]

The effect of scandium additives on structure and mechanical properties of cast metal, sheet semi-finished products and butt joints made by nonconsumable electrode argon-arc welding of aluminum alloys of Al-Zn-Mg-Cu alloying system was studied. It is shown that scandium-containing alloys, both in the cast metal, and in their sheet semi-finished products, all the structural components have smaller dimensions, than in the alloys without scandium, that ensures the ultimate strength of the sheets on the level of 640-700 MPa, depending on content of main alloying elements in them. It is established that in nonconsumable argon-arc welding of 3 mm sheets from scandium-containing alloys the total length of the softening zone is reduced by 20 % at simultaneous increase of weld metal hardness that provides higher mechanical properties of such joints. Complex addition of scandium to base material and filler wire simultaneously that ensures its content in the weld metal on the level of 0.30-0.35 % allows significantly increasing the resistance of welded joints of Al-Zn-Mg-Cu system to hot solidification cracking. 16 Ref., 3 Tables, 4 Figures. [ABSTRACT FROM AUTHOR]

Three-layer honeycomb panels are widely applied in aircraft construction, ship-building, construction and others industries. In terms of design, they consist of a honeycomb core and two skins. At relatively small weight, these structures are characterized by high strength values, sound- and heat-insulating properties. The main problem in manufacturing a three-layer structure is welding the upper and lower skins to end faces of the honeycomb core. The work presents the results of development of the technology of manufacturing three-layer honeycomb panels of 150×150 mm size from aluminium alloys. The honeycomb core from AD1 aluminium alloy 0.150 mm thick was produced by joining the corrugated strips into blocks by spot welding. Flatness of end faces of the honeycomb core was achieved by grinding. The structure rigidity was ensured by filling the cells with colophony. Joining of the core to the skins from AMg2 alloy 1.0 mm thick was performed by diffusion welding in vacuum. The process was conducted in a fixture consisting of the lower and upper flanges and bushing. The flanges provided skin pressing to the honeycomb core end faces over the entire contact area, and the bushing allowed homogenizing the temperature field in the item and controlling the extent of its deformation during welding. 8 Ref., 1 Table, 6 Figures. [ABSTRACT FROM AUTHOR]

Three-layer panels with periodic cellular core from aluminium alloys are promising for application in aerospace products, ground and water transportation. The uniqueness of the three-layer panel design consists in that they are characterized by high values of strength and rigidity at a relatively small mass. The work deals with the main types of three-layer panels, design features of manufacturing the cores, methods to join the honeycomb core strips to each other, as well as the three-layer panel elements into one structure. The objective of the presented review is analysis of modern methods of manufacturing three-layer panels from aluminium alloys. Analysis of published data showed that such methods of joining the three-layer panel elements as adhesive bonding and brazing became the most widely applied. Their main disadvantage, however, is increase of the structure mass due to application of an adhesive or braze alloy. Application of diffusion welding with manufacture of honeycomb core from a stronger titanium alloy for joining three-layer panels or application of a specialized fixture, which allows limiting the degree of plastic deformation of the structure, are promising for welding three-layer panels. 28 Ref., 1 Table, 9 Figures. [ABSTRACT FROM AUTHOR]

The paper deals with the influence of diffusion welding parameters on formation of joints from foil of Ni-20Cr powder alloy 25 mm thick. It is shown that welding of nichrome alloy in the temperature range of 800-1200 °C without application of interlayers does not allow producing defectfree joints. Features of formation of Ni-Cr alloy joints at application of interlayers from foils, produced by the technology of electron beam deposition and condensation in vacuum were studied. Foil with multilayer structure of Ni-Al, Ti-Cu systems and foil with porous structure from Cu, Ni and Cr was used in the work. Microstructure and chemical composition of the joints were studied, using optical and electron microscopy. Strength properties of metal in the joint zone were assessed by the results of microindentation and tensile testing of flat samples. It is found that application of such interlayers in welding allows producing defectfree microstructure of the joint zone. It is shown that joints with strength properties on the level of those of base metal are formed in welding through an interlayer from copper-based porous foils. [ABSTRACT FROM AUTHOR]

Comprehensive investigation of mechanical and physical properties of diffusion zone of the produced joints was performed as part of fulfillment of the technological task, namely producing superlight welded structures from porous aluminium alloys of Al–Mg–Zn system and monolithic magnesium alloys (ML4 standard alloy of Mg–Al–Zn system and experimental alloys of Mg–Ga system). The objective of the study was evaluation of the influence of heating cycle, characteristic for different welding processes, on the joints. Welding was performed by two methods with maximum heating temperature up to 300 °C: diffusion welding with long-term cycle of heating in vacuum, and welding with heating by passing current in air, which is characterized by short heating cycle. Gallium was used for forming a monolithic joint and diffusion activation. It is found that a diffusion zone about 10 mm wide forms on porous aluminium side, with slight lowering of micromechanical properties in pore walls, that is typical for aluminium alloys at contact with gallium. In magnesium alloys, an extended (60–100 mm) wavy intermetallic-strengthened diffusion zone forms along the joint line in both the welding processes, mostly of Mg5Ga2 composition with melting temperature of 456 °C that is higher than the welding temperature. Thus, the possibility of joining porous alloys to monolithic ones is shown at their slight heating and chemical activation of the joint zone by gallium. [ABSTRACT FROM AUTHOR]

Development of thermal protection systems is one of the important engineering problems that should be solved at development of reusable space vehicles. Metal panels of thermal protection systems should consist of separate tiles with individual fastening to load-carrying structure of space vehicle, with surface density of not more than 10 kg/m2, capable of withstanding multiple long flights and providing temperature lowering from 1100 °C on the outer wall to 200 °C on the inner wall. The work shows the results on development of the technology of vacuum diffusion welding of a three-layer honeycomb panel from experimental powder alloy YuIPM-1200. Technological samples of three-layer honeycomb panel were made from this alloy, and their testing was performed in the working temperature range. [ABSTRACT FROM AUTHOR]

Friction assemblies based on steel and bronze are widely applied in many mechanical systems. Steel and bronze joints are produced by diffusion welding at temperatures of 750—850 °C. Defect formation in the joint zone in a number of cases is associated with high welding temperature. The paper deals with the possibility of lowering diffusion welding temperature by interlayer application in the case of making permanent joints of steel (20Kh3MVF) and bronze (BrOSN 10-2-3). Porous nickel and copper foils, produced by vacuum deposition, were used as interlayers. It is shown that application of such porous interlayers allows welding temperature to be lowered to 660—700 °C. Lowering of welding temperature prevents growth of liquation precipitates of tin and lead in the joint zone, that lowers the probability of defect formation. The thus produced joints are stable at short-time heating to 800—850 °C, that allows later on performing heat treatment of steel as part of composite material to increase its strength properties. [ABSTRACT FROM AUTHOR]

Features of formation of permanent joints by diffusion welding through an intermediate interlayer based on porous nickel, produced by vapour phase vacuum deposition (EB PVD) were studied in the case of stainless steel Kh18N10T. It is shown that application of vacuum porous nickel condensates promotes lowering of temperature-force parameters of diffusion welding (welding temperature of 800 °C + cyclic load with 20 MPa amplitude). Such an influence of the interlayer on the conditions of producing the welded joints is associated with superplastic behaviour of porous nickel and its non-equilibrium structure (small grain size and presence of vacancy type defects). It is established that pore healing in the interlayer is observed and diffusion processes between the interlayer and stainless steel are activated during diffusion welding. This results in formation of a defectfree zone of the joint based on nickel, alloyed with iron and chromium with strength properties only slightly different from those of base metal. [ABSTRACT FROM AUTHOR]

Thermal protection tile structures, made from heat-resistant materials, are widely applied for protection of space vehicle bodies. Carbon-carbon composite materials, high-temperature metal alloys and structural ceramics can be used as high-temperature heat-resistant materials for manufacturing thermal protection structure tiles. The presented work gives calculation-theoretical assessment of strength properties of combined tiles of thermal protection structure of returnable space vehicles, having a metal external load-carrying element and body from carbon-carbon composite material, as well as tiles from carbon-carbon and ceramic materials. The advantages and disadvantages of each of the studied thermal protection tile systems are considered. Strength analysis is used to determine the dimensions of load-carrying elements for bodies of thermal protection structures, meeting the requirements of strength, stability and resistance to flutter, and weight of each structure. It is found that thermal protection tiles with a body from carbon-carbon composite materials and tiles with an external three layer honeycomb panel from YuIPM-1200 alloy have the best weight and strength characteristics. [ABSTRACT FROM AUTHOR]

The problem of effect of solidification rate on structure of weld metal of scandium-containing aluminium alloys is considered. Peculiarities of scandium precipitation from melt in solidification of aluminium alloys under non-equilibrium conditions, simulating fusion welding, are investigated. Procedure of investigations has been developed and confirmed experimentally. Advantage of offered procedure over the existing ones consists in the fact that it allows simulate almost all the methods of fusion, from argon arc non-consumable electrode welding to electron beam welding. It is shown that the procedure satisfies the put aims completely. Microstructural investigations of ingots in height showed that within the interval of solidification rates from 103.3 to 102.5 °C/s the change of form of solidification occurs from dendritic to subdendritic ones. It was found that at rates of solidification, commensurable with solidification of weld metal, up to 0.41 % Sc can be contained in solid solution of alloys. When applying the highly concentrated power sources, such as electron beam, it is possible to reach the similar value also in welds. In arc methods of welding approximately 0.3 % Sc can be assimilated in solid solution of weld metal. It was found that it is necessary to provide its content in weld metal at the level of 0.35-0.40 wt.% to maximization of effect from alloying of welds with scandium. In this case the increase in mechanical properties of weld metal is provided both by refining of its crystalline structure, and also by hardening the solid solution by scandium. [ABSTRACT FROM AUTHOR]

The possibility of a combined use of titanium and aluminium alloys in the form of permanent joints is of high interest to many industries. However, no investigations involving evaluation of the effect of the diffusion welding process on distribution of chemical elements and microstructure of the welded joints have been conducted so far. As revealed by the metallographic examinations carried out in this study, magnesium during the welding process diffuses from alloy AMg6 to the zone of joining with alloy VT6 and accumulates in the contact region. An interlayer of aluminium AD1 was used to eliminate the negative effect of magnesium. A gradual decrease in the concentration of magnesium from AMg6 to AD1 was observed in the joining zone when using the aluminium interlayer. A region of diffusion interaction, in which titanium and vanadium diffused from VT6 to AD1, was detected in the AD1 + VT6 joining zone. It can be concluded from the investigation results that in vacuum diffusion welding of titanium alloys to aluminium alloys containing magnesium the use of the interlayer of pure aluminium provides the sound welded joints with a gradual distribution of magnesium in the joint. The main role in formation of the titanium alloy to interlayer joint is played by the processes of diffusion of titanium and vanadium in a direction of the interlayer. [ABSTRACT FROM AUTHOR]