Kushnareva O. Peculiarities of structure and structural strength of welded joints of aluminum alloys of Cu-Li-Sc alloying system

The thesis is devoted to investigation of effect of changes in structure and chemical composition of metal of 1460 aluminum-lithium welded joints depending on character of filler wire alloying (with or without Sc) in as-welded and heat-treatment conditions (ageing - T=150 C, 22 h and annealing - T=350 C, 1 h) and as a result of external loading. The thesis contains investigation of microstructure of welded joints using complex of methods (light, analytical scanning and transmission electron microscopy). Analytical evaluation of joint properties was performed allowing determination of optimum structural and phase compositions of weld metal and HAZ. It is determined that Sc alloying promotes rise of values of yield strength in welded joint up after annealing. Phase formations and substructure have the highest effect during strengthening. The thesis states that shear bands with gradients of local internal stresses are formed at dynamic loading in weld metal without Sc. This is one of the reasons of crack formation. It is shown that the precipitations, consisting of Al3Sc core and Al3Li shell as well as based on Al2Cu of complex composition (with 15-40% Al3Sc), which promote structure fragmentation and more uniform distribution of local internal stresses, are formed in the case of Sc alloying. It is proved that this rises the possibility of plastic relaxation of stresses due to connection of rotation mechanisms to dislocation ones at simultaneous increase of strength and technological ductility of welded joints.