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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 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]

Influence of zirconium and scandium modifiers in the filler wire and of arc oscillations due to electric current flowing through the filler section in nonconsumable electrode argon-arc welding, as well as of friction stir welding process on formation of weld structure in sheet aluminium alloys 1460 and 1201, was studied. Curves of metal hardness distribution in the zone of permanent joint formation were plotted, and ultimate strength of samples was determined directly after welding and after their artificial ageing. It is shown that application of friction stir welding yields higher values of ultimate strength of the metal of welds and welded joints on aluminium alloys 1460 and 1201, than in automatic nonconsumable electrode argon-arc welding with weld pool oscillations, even at application of welding wire with zirconium and scandium. Here, the maximum strength level (75 % for alloy 1201 and 86 % for alloy 1460), compared to base material, is achieved after artificial ageing of samples, at which phase insformations and processes of stabilization of the structure of metal after thermal impact, take place. [ABSTRACT FROM AUTHOR]

A series of research was performed to study the characteristics of structural strength of butt joints of aluminium alloy D16T 2 mm thick, produced by friction stir welding. Features of weld formation and degree of metal softening in the zone of the produced permanent joint were analyzed. Mechanical testing of welded joint samples was performed at static and cyclic loading. Diagrams of fatigue crack growth rates in the base metal, heat-affected zone and thermomechanical impact zone, on the boundary of these zones and in the weld metal were plotted. It is shown that the characteristics of cyclic crack resistance of weld metal of these joints are more than two times higher than the respective values for base metal that is indicative of the good prospects for application of friction stir welding in fabrication of critical structures from D16T alloy. 19 Ref., 8 Figures. [ABSTRACT FROM AUTHOR]

The work presents the results of studying harmful substances in the air, released during nonconsumable electrode argon-arc welding of 1201 (Al-Cu-Mn) and 1460 (Al-Cu-Li) aluminium alloys. The objective of this work is performance of sanitary-hygienic assessment of the nature of aerosol and gas evolution from these alloys, in order to ensure favourable sanitary-hygienic working conditions for welders. It is shown that for 1460 alloy with lithium the intensity of welding aerosol formation is 1.5 times higher, and ozone concentration exceeds the maximum admissible concentration 3-4 times in the same welding modes. 13 Ref., 4 Tables, 5 Figures. [ABSTRACT FROM AUTHOR]

A complex of investigations was carried out to study the strength characteristics of welded butt joints of structural aluminum alloy D16 of 2 mm thickness, produced by friction stir welding. It was shown that the use of friction stir welding provides the formation of a permanent joint with a minimum level of stress concentration in the transition zones from the weld to the base material and allows avoiding the formation of defects in the welds such as pores, macroinclusions of oxide film and hot cracks caused by melting and crystallization of metal in fusion welding. As a result of intensive plastic deformation in the weld metal, a homogeneous disoriented structure with a grain size of 3-4 µm and with dispersed phase precipitations of not more than 1 µm is formed, and in the regions adjacent to it the elongation and distortion of grains in the direction of movement of the plasticized metal occurs in the zone of thermomechanical action. Due to this, the hardness of metal in the joint zone, the tensile strength under uniaxial tension and the fatigue strength under cyclic loads are increased. [ABSTRACT FROM AUTHOR]

The paper analyzes the structural features, strength and fatigue life properties of sheet joints of Al-Li alloys 1420 and 1460, produced by nonconsumable-electrode argon-arc welding and friction stir welding. It is shown that application of FSW provides formation of permanent joints with minimum level of stress concentration in the points of weld transition to base material and allows avoiding defects in welds in the form of pores, oxide film macroinclusions or hot cracks due to melting and solidification of metal in fusion welding. Here, intensive plastic deformation of metal under the tool shoulder and in weld nugget results in formation of fine-crystalline (3-4 μm) uniform disoriented structure, and grain elongation and distortion in the direction of plasticized metal displacement proceed in adjacent sections. This leads to increase of hardness and ultimate strength of joint weld metal. Lowering of the temperature of heating of the edges being welded provides reduction of maximum level of tensile residual longitudinal stresses in welded joints, compared to TIG welding. It is found that fatigue resistance characteristics of butt welded joints, made by FSW, are superior to those of the joints, made by TIG welding. [ABSTRACT FROM AUTHOR]

An essential difference in formation of structural-phase state at application of different welding conditions -- friction stir welding compared to argon-arc welding -- is considered in the case of welded joints of complex aluminium-lithium alloys. The urgency of comprehensive experimental-analytical assessment of interrelation of welded joint structure and properties is also shown. Assessments of specific contribution of structural-phase state (chemical composition, phase dimensions, grain, subgrain and dislocation structure) into the change of the main service properties of welded joints made by argon-arc welding and friction stir welding are considered, as well as the influence of welded joint structural state on the nature of distribution, level of growing internal stresses and their relaxation mechanisms under specific welding conditions. [ABSTRACT FROM AUTHOR]

Comparative studies were performed of microstructure, degree of softening, ultimate strength, crack initiation and propagation susceptibility and fatigue resistance of welded joints of wrought aluminium alloys AMg5M andAMg6M 1.8 mm thick, produced by nonconsumable-electrode argon-arc welding and friction stir welding, as well as of the levels of residual longitudinal stresses developing in them. It is shown that application of FSW enables formation of permanent joint with minimum level of stress concentration in weld-to-base metal transition areas, and allows avoiding defects in the form of pores, oxide film macroinclusions and hot cracks in welds due to metal melting and solidification in fusion welding. Intensive plastic deformation of metal results in formation of a uniform disoriented structure under the tool shoulder and in the weld nugget with grain size of 3-4 μm and disperse (not more than 1 μm) phase precipitates, and grain elongation and distortion in the direction of plasticized metal displacement occur in the adjacent areas. This leads to increase of metal hardness in the joint zone, sample ultimate strength at uniaxial tension, their fatigue strength and lowering of crack initiation and propagation susceptibility. Lowering of temperature of welded edges heating leads to lowering of maximum level of residual longitudinal stresses in welded joints by 25 %, compared to TIG welding. [ABSTRACT FROM AUTHOR]