PSI - Issue 50

Aleksandr Malikov et al. / Procedia Structural Integrity 50 (2023) 170–177 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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been created Rioja and Liu (2012). New high-strength heat-hardenable, deformable alloys of various systems have been created, for example: Al-Mg-Li-X (X = Zn, Mn, Zr, Sc), Al-Cu - Mg-Li, Al-Cu-Li-X (X = Mg, Zn, Mn, Zr, Sc). Alloys of the Al-Cu-Li-X system, alloys of the Al-Mg-Li-X system have high mechanical characteristics, medium strength, high corrosion resistance and light weight. Corrosion-resistant 1420, 1424 alloys of the Al-Mg-Li system are the most promising alloys for replacing traditional AMG6 and AMG5 alloys of the Al-Mg-Mn system in the aviation and space industry. This is because they have higher strength and fatigue characteristics compared to traditional aluminum alloys. Detailed studies of the properties of these alloys are being carried out, methods are being developed for changing the strength characteristics and structural-phase state due to various methods of thermal (hardening, artificial aging, annealing) and deformation (plastic deformation) processing. In order to replace the rivet joint and thereby reduce the weight of the structure, welding technologies for these Al-Li alloys, as well as their foreign counterparts, are being actively developed in various ways: friction stir welding, laser welding, laser welding with filler wire, electron beam welding, argon - arc welding (Oladimeji and Taban, (2016); Shiganov et al. (2017); Xiao and Zhang (2014). However, welded joints of these alloys obtained by fusion welding have low mechanical properties. The tensile strength of the welded joint of alloys of the Al-Mg-Li system is 0.60-0.85 of the strength of the base material. The main reasons for the decrease in the strength of a welded joint are the burnout of volatile alloying elements such as magnesium, lithium, zinc, manganese, the formation of porosity and hot cracks in the weld. According to various sources, to reduce the influence of these factors, either optimization of welding modes is carried out, or an additive material is used. The authors in Fu et al. (2014); Ning et al. (2017) carry out comparative studies of two methods of laser welding of the 2A97 alloy with and without wire, and study the microstructure and strength properties. The strength of the welded joint is 0.84 of the strength of the base alloy. Han et al. (2017), the process of obtaining T joints by laser welding of Al-Li alloys 2060-T8/2099-T83 using a wire was studied, the phase composition of the joints, and mechanical characteristics were studied. Cui et al (2012), laser welding of Al-Li alloy 5A90 was studied, and comparative studies of the microstructure, microhardness of the welded joint and the base alloy were carried out. However, this does not take into account that these alloys are thermally and mechanically hardenable. Aluminum alloys of the Al-Mg-Li system are characterized by a complex phase composition, which changes during heat treatment. This is due to the use of a larger number of alloying elements compared to traditional alloys. For example, alloy 1424 contains Mg, Li, Zr, Sc. Zn. Alloying elements can enter into a chemical reaction with aluminum, as a result of which, in addition to the main strengthening phase δ – Al3Li, ternary and double intermetallic phases (for example, S1 – Al2MgLi) are formed in the alloys, which have a significant effect on the strength and ductility of the material. At the same time, as it has been shown Malikov et al. (2019, 2021b, 2021a), that in order to increase the strength of the welded joint of heat-strengthened Al-Li alloys, it is necessary to carry out additional mechanical and thermal treatment of the weld joint. The aim of the work is a comprehensive study, including laser welding using filler aluminum wire of the Al-Mg Mn system and post weld heat treatment in order to improve the level of mechanical properties of alloys of the Al Mg-Li system. 2. Materials and Methods To develop a technology for producing high-strength laser welded joints of structural materials for aviation purposes with a filler wire, an aluminum-lithium alloy of grade 1420 was chosen. Corrosion-resistant alloy 1420 of the Al-Mg-Li system is the most promising alloy for replacing traditional AMg6 and AMg5 alloys (Al-Mg-Mn system) in the aviation and space industry Grushko et al. (2016). This is because it has higher strength and fatigue characteristics, as well as increased corrosion resistance compared to traditional aluminum alloys of the Al-Mg system. The analogue of 1420 alloy is 5A90 alloy. 5A90 alloy of the Al-Mg-Li system is beginning to be widely introduced into the aerospace industry Tian et al. (2020); Xiao et al. (2020). A wire made of lithium-free aluminum alloy AMg6 was chosen as a filler wire. This choice of filler wire was made because the concentration of the alloying element Mg in it is close to the concentration of Mg in alloy 1420. In addition, AMg6 is the most durable of the industrial alloys of the Al – Mg system and is increasingly used for the manufacture of welded structures.