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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]

Light metal alloys (in particular, beryllium and aluminium) are applied in different engineering fields, for instance for fabrication of rocket and aircraft elements. When designing such engineering elements, there is the need to produce welded joints with different types of welds. Laser welding with nonthrough thickness penetration can be used for item sealing, welding-on flanges and welding thin-walled structures of up to 2-3 mm thickness. Toxic fumes form in welding beryllium alloys. Such a peculiarity requires reducing the number of technological experiments, aimed at selection of mode parameters. An up-to-date approach to solving the problem of light alloy welding is performance of preliminary calculated determination of mode parameters with their further experimental verification. Technological verification can be performed on high-strength aluminium alloys close by their physico-mechanical characteristics to beryllium alloys. Therefore, this work is devoted to preliminary determination of mode parameters of laser welding by a sealing weld with nonthrough thickness penetration of thin-walled flanges of cylindrical parts and box-shaped items from light metals and alloys based on Be and Al, taking into account the temperature of heating after welding. A procedure of preliminary calculated determination of mode parameters of laser welding of parts from a berylliumbased alloy is proposed in the work, which is suitable for both through-thickness and nonthrough-thickness penetration. Nonthrough-thickness penetration can be applied for welding-on flanges by a sealing weld. Experimental verification on samples from alloys of Al–Zn–Mg–Cu system and comparison with published data on beryllium alloy welding showed that the error of the proposed procedure is in the range of up to 15 – 20%. [ABSTRACT FROM AUTHOR]

Research papers devoted to development of laser-plasma processes during the last two decades are reviewed. It was found that the current directions of scientific research of the processes of laser-plasma welding are focused mainly on studying the peculiarities of joint impact of constricted arc plasma and laser radiation with wave length of 1.03 – 1.07 μm (first of all, fiber laser) on steels and alloys, as well as studying the physical fundamentals of manifestation of the synergic (hybrid) effect at such an impact and determination of the possibilities of its practical application. It was determined, in particular, that increase of the effectiveness of synergic effect manifestation is related to improvement of the plasma arc burning conditions in the zone of ionized vapour plume, which forms under the impact of focused laser radiation, as well as simplification of laser keyhole formation due to plasma arc pressure. Ref. 49, Fig. 9. [ABSTRACT FROM AUTHOR]

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]

The paper deals with the features of laser welding with incomplete (non-through thickness) penetration of high-strength aluminium alloys of 7ххх series. It was found that at joining of 1.5 mm sheets by fibre laser welding to the depth of 0.5…0.7 mm there arises the risk of formation of pores, in particular, in the root zone, streaks of oxide film in the weld lower part, as well as hot cracks. The latter can be eliminated by reducing the heat input below 25 – 30 J/mm. The weld metal is characterized by an equiaxed finely dispersed structure with grain size of 10…15 ~m for 7005 alloy and 15…25 ~m for 7075 alloy. In the fusion zone, the grains are of an elongated shape with 2.5…3.0 coefficient for 7005 alloy and 2…5 for 7075 alloy. In the HAZ the grain length is reduced, the shape coefficient becomes 3…5 and 3.0…3.5 for 7005 and 7075 alloys, respectively. At performance of laser welding with small (~5 J/mm) values of the heat input, microhardness of the welds and HAZ is rather uniform, and close to that of the base metal. For 7075 alloy microhardness drop to 20% was observed in the fusion zone region, that is due to formation of grains of an elongated shape with shape coefficient of 2…5. The found drawbacks can be eliminated through reduction of pulsations of the vapour-gas channel with simultaneous increase of the stability of its existence and introduction of cathode breaking of the oxide film. [ABSTRACT FROM AUTHOR]

The paper confirms the presence of synergic effect at laser-plasma welding, using fiber laser, by comparing the cross-sectional areas of beads deposited in AISI 304 plate (δ = 4 мм) by laser, plasma, and hybrid processes at close power values of laser radiation and plasma arc (~2 kW each). It is determined that the manifestation of this effect depends on welding speed. At the speed of 2 m/min the hybrid bead cross-sectional area can exceed the sum of areas produced with the laser and plasma processes by up to 30%, and for the speed of 4 m/min by ~20 %. Comparison of input energy of the laser and hybrid processes of stainless steel welding showed that the difference between them depends on the welded sheet thickness (or penetration depth). This value first decreases from ~100 % for sheets with δ = 2 mm to 50 % for sheets with δ = 6 mm, and at further increase of penetration depth it rises to 60 %. The nature of dependencies of the factor of area ratio φ, weld geometry К and penetration depth Ф on the speed of hybrid welding of AISI 304 steel allows recommending the range of speeds of 1.5…2.0 m/min, as a more acceptable by the criteria of synergic effect and penetration depth. It is found that at hybrid welding with application of fiber laser radiation, the plasma component promotes elimination of such defects of weld upper bead formation, characteristic for laser welding, as undercuts and a ridge, etc. [ABSTRACT FROM AUTHOR]