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The effect of change in the speed of movement of the heating source in plasma-arc welding of aluminium alloys of 2.0 mm thick of three Al–Mg–Mn (AMg5M, AMg6), Al–Cu–Mn (1201) and Al–Cu–Li (1460) alloying systems on the microstructure and hardness of the weld metal and near-weld zone, on the formation of inner pores and mechanical properties of welded joints was considered. Changes in the distribution of temperature fields and indices of the stress-strain state of welded specimens were analyzed. It was found that for each type of alloys there is a certain “peak” welding speed, with exceeding of which there is no significant reduction in residual deformations and stresses, as well as a decrease in the width of the base metal heating zone. Instead, mechanical properties of welded joints are deteriorated because of an increase in the number of pores in the weld metal and the formation of inadmissible undercuts in the upper part of the weld in the area of transition from the weld to the base metal. On the example of Al–Mg–Mn alloy it is shown that such regularities are also typical not only for the thickness of 2.0 mm, but also observed during welding of specimens with the range of thicknesses of 4–8 mm. This allows using these results to predict indices of strength of the welded joint and weld metal for these thicknesses when the speed of plasma-arc welding at a variable polarity asymmetrical current is increased higher than the “peak” value. [ABSTRACT FROM AUTHOR]

Results of welding a wide range of light alloys by highly-concentrated heat sources have been analyzed. It is shown that the characteristic defects are hot cracks, internal pores, HAZ softening, weld sagging, undercuts and irregular reinforcement bead formation. It was found that in order to produce sound joints, it is necessary to thoroughly select welding mode parameters, remove the oxide film from billet edges before welding, ensure reliable protection of the weld pool, and in some cases and it is rational to apply preheating or concurrent heating. One of the advanced methods to minimize the susceptibility to formation of the above-mentioned defects is application of hybrid laser-arc and laser-plasma welding processes. The welds produced by electron beam and laser (СО2 - and fiber-optic lasers) welding processes are quite similar visually, by their macrostructure, as well as the main characteristics. The weld strength parameters and heat input required for full penetration of the metal are somewhat different for different welding methods (for fiberoptic laser it is usually 30 % less). 54 Ref., 3 Tabl., 8 Fig. [ABSTRACT FROM AUTHOR]

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It is shown that to increase the productivity of robotic fabrication of fragments of steel truss RHS (Rectangular Hollow Section) structures it is advisable to make workpieces by precision laser cutting with subsequent assembly of fragments by point tack and consumable-arc seam welding with current-carrying (hot) filler wire. Laser cutting with radiation power of ~1.0 kW and compressed air blowing at the pressure of 1.5 MPa allows obtaining ready for further welding elements of RHS structures with the accuracy of 0…0.1 mm. It is established that in the case of application of consumable-arc welding with hot filler wire, the speed increases by ~1.5 times compared to conventional consumable-arc welding 13 Ref., 6 Fig. [ABSTRACT FROM AUTHOR]