High cycle fatigue behaviour of thin sheet joints of aluminium-lithium alloys under constant and variable amplitude load
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RESEARCH PAPER
High cycle fatigue behaviour of thin sheet joints of aluminium-lithium alloys under constant and variable amplitude loading Sviatoslav Motrunich 1
&
Illia Klochkov 1 & Anatoliy Poklaytsky 1
Received: 11 November 2019 / Accepted: 30 July 2020 # International Institute of Welding 2020
Abstract The main purpose of this work is to establish high cyclic fatigue behaviour of sound welds of aluminium alloys of Al-Mg-Li and Al-Cu-Li doping system under constant and variable amplitude loading. Sound welds of thin sheet (1.8 and 2.0 mm) aluminiumlithium alloys 1420 and 1460 were produced by tungsten inert gas (TIG) and friction stir welding (FSW) technologies. Microstructure investigations, hardness and residual stress measurements, tensile and fatigue tests of welds were performed. It is shown that FSW joints have fine grain microstructure in weld nugget with homogeneous disoriented structure and elongation and deviation of grains in a direction of plasticized metal movement, taken place in adjacent areas. Hardness on joints face was measured, showing areas of softening near the weld. Lower temperature of welded edges heating reduces the maximum level of longitudinal residual tensile stresses in FSW joints in comparison with TIG welds. Tensile strengths of TIG and FSW joints were obtained. The high cycle fatigue tests of FSW and TIG joints under constant and variable amplitude loading were performed. It is shown that fatigue behaviour of FSW joints exceeds the characteristics of the joints obtained by TIG welding. Keywords Aluminium alloys . Welding . Microstructure . Tensile strength . Fatigue . Variable amplitude loading
1 Introduction Aluminium has been used in many high-performance structures such as military and commercial aircraft, navy vessels, yachts, high-speed automotive and railway transport. Future aircraft designs are attempting to maximize the usage of aluminium structures to achieve maximum weight savings and provide more efficient and cheaper transportation. The use of high-strength and corrosion-resistant aluminium-lithium alloys with low density and high-elasticity modulus can reduce fuel consumption and improve the functional capabilities of the aircraft and space vessels. Alloy 1420 (Sm ≈ 459 MPa, S0.2 ≈ 322 MPa density 2.4 g/cm3) of Al-Mg-Li doping system contains 4.5 to 6.0% Mg and 1.8 to 2.3% Li. It has a Recommended for publication by Commission XIII - Fatigue of Welded Components and Structures * Sviatoslav Motrunich [email protected] 1
E.O. Paton Electric Welding Institute of the National Academy of Science of Ukraine, 11 Kazymyr Malevich St., Kyiv 03150, Ukraine
specific gravity 12% lower, and its Young modulus is 8% higher than of 2024 alloy commonly used in aircraft industry [1]. The high strength alloy 1460 (Sm ≈ 565 MPa, S0.2 ≈ 523 MPa, density 2.6 g/cm3) belongs to Al-Cu-Li doping system (nominal composition Cu ≈ 3%, Li ≈ 2%) with additions of zirconium and scandium. It has a high level of strength and ductility at cryogenic temperatures that indicate the prospect
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