Investigation of the phase composition and mechanical characteristics of laser welded joints of aluminum-lithium alloys

A study of laser welding of modern aluminum-lithium alloys has been carried out. Optimization of post heat treatment of laser welded joints has been carried out. The change in the structural-phase composition of welded joints was investigated. The strength of welded joints after heat treatment was equal to the strength of the base alloy.

DEVELOPMENT OF A TECHNOLOGICAL PROCESS FOR MANUFACTURING WELDED STRUCTURES

the main goal of this article is to obtain welded permanent joints of modern thermally hardened aluminum and aluminum-lithium alloys made by laser welding, having mechanical characteristics (temporary tensile resistance, yield strength, elongation at break) and structural-phase composition close to or equal to the base alloy. It is shown for the first time that by controlling the parameters of heat treatment of samples with a welded joint of all studied aluminum-lithium alloys, it is possible to purposefully influence the formation of the specified mechanical properties of the weld by changing the structural and phase composition of the weld. The evolution of the struc-tural and phase composition of welded joints of thermally hardened aluminum and aluminum-lithium alloys has been investigated using modern independent diagnostic methods: for the first time, the use of synchrotron radia-tion diffractometry in combination with high-resolution transmission, scanning electron and optical microscopy. The dependences of the increment of deformation under cyclic loading with amplitudes exceeding the elastic limit on temperature are established. For untreated welded joints, it was found that at +85 C, the inhomogeneity of the deformation increment increases, and its speed increases by 8 times for alloy 1461, 5 times for alloy 1420 and 1.5 times for alloy 1441. At a temperature of -60 0C, alloys 1420 and 1461 have hardening stages, during which the value of deformation decreases at given boundary stress values. At +20 0C, there is a uniform increment of defor-mation and an increase in the amplitude of deformation with an increase in the amplitude of stress. At +85 0C, the strain amplitude does not change with increasing stress amplitude, its value is 0.55-0.5 of the strain amplitude at +20 0C. Based on the research results, technological techniques have been developed that allow obtaining me-chanical characteristics and structural-phase compositions of welded joints close to the main alloy during laser welding of aviation thermally hardened aluminum and aluminum-lithium alloys of the Al-Mg-Cu. Al-Mg-Li, Al-Cu-Mg-Li, Al-Cu-Li systems.

Microstructure Analysis and Fatigue Behavior of Laser Beam Welding 2060-T8/2099-T83 Aluminum–Lithium Alloys

In this paper, the microstructure analysis and performance research of dual laser beam welded 2060-T8/2099-T83 aluminum–lithium alloys were carried out. First, the macroscopic morphology and microstructure characteristics of T-joint aluminum–lithium alloys under different welding conditions were observed. Then the effect of welding parameters and pore defects on tensile and fatigue properties of the weld were carried out and the experimental results were analyzed. It was found that the weld heat input has a significant influence on the penetration of the welded aluminum–lithium alloys joint. When the laser power is too high, the weld will absorb more laser energy and the increase in the evaporation of magnesium will further increase the weld penetration. When the penetration depth increases, the transverse tensile strength tends to decrease. There is no obvious rule for the effect of pore defects on the tensile strength of the weld. At the same time, the heat input of the weld is inversely proportional to the porosity. When the weld heat input increases from 19.41 to 23.33 kJ/m, the porosity decreases from 5.35% to 2.08%. During the fatigue test, it was confirmed that the existence of pore defects would reduce the fatigue life of the weld. In addition, from the analysis of the fatigue fracture morphology it can be found that when the porosity is low, the weld toe is the main source of fatigue cracks. The crack propagation zone shows a typical beach pattern and the final fracture of the base metal presents the characteristics of a brittle fracture. While, when the porosity is high, the crack source is mainly located at the pore defects. T-joint fractures from the inside of the weld and the fracture in the final fracture zone have obvious pore defects and dimples.

Development of hot deformation rheological model as exemplified by 1424 and V-1461 aluminum-lithium alloys

The article proposes a variant of the rheological model of hot deformation – the law of hyperbolic sine, which, in contrast to the standard one, takes into account not only the strain rate and process temperature, but also the strain ratio. Material constants included in the law of hyperbolic sine are replaced by polynomial functions of the strain ratio with coefficients calculated using the corresponding method developed. The paper describes applications of the rheological model proposed in low-density aluminum-lithium alloys 1424 of the Al–Mg–Li–Zn system and V-1461 of the Al–Cu–Li–Zn system, for which flow curves in the temperature range 400–480 °C and strain rate range 1–60 s–1 up to a strain ratio of 0.6 are defined by physical simulation at the Gleeble 3800 unit. The influence of the initial material state was also investigated – samples were taken from both the ingot and hot-rolled plates. Constants were determined for the rheological model of hot deformation including the Zener–Hollomon parameter and the law of hyperbolic sine for the entire range of stresses and strains. After approximating the dependences of the model parameters on true strains with a 4th degree polynomial law, a rheological model was created that describes the alloy behavior in the temperature-rate range under study. The features of changes in hyperbolic sine law parameters depending on the strain ratio were established. It was shown that, in general, parameters for the cast material are higher than for the rolled one. A comparison between the standard and proposed models showed that the use of the standard model over the entire strain interval leads to too high flow stress values (up to 12 %).

Designed layered materials based on sheets of aluminum-lithium alloys and fiberglass in the designs of new generation aircrafts

The developments in the field of layered aluminum-fiberglass using sheets of aluminum-lithium alloys and layers of fiberglass are presented. A set of basic indicators is considered depending on the stacking of layers in the structures of aluminum-fiberglass СИАЛ. The tests show the advantages of structures using laminated hybrid materials over structures made of traditional aluminum alloys. Keywords: laminated hybrid material, aluminum-fiberglass СИАЛ, GLARE, aluminum-lithium alloy, structurally similar specimen. [email protected]