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Aluminum-Lithium Alloys
Because lithium is the least dense elemental metal, materials scientists and engineers have been working for decades to develop a commercially viable aluminum-lithium (Al-Li) alloy that would be even lighter and stiffer than other aluminum alloys. The first two generations of Al-Li alloys tended to suffer from several problems, including poor ductility and fracture toughness; unreliable properties, fatigue and fracture resistance; and unreliable corrosion resistance. Now, new third generation Al-Li alloys with significantly reduced lithium content and other improvements are promising a revival for Al-Li applications in modern aircraft and aerospace vehicles. Over the last few years, these ne...
Aluminum-Lithium Alloys
Mechanical working of Al–Li alloys is primarily concerned with aerospace alloy rolled products (sheet and plate), extrusions, and to a lesser extent forgings. These products are fabricated by hot working with intermittent and final heat treatments. This thermomechanical processing (TMP) can be rather complex for the modern 3rd generation Al-Li alloys, but is necessary to obtain optimum combinations of properties. This Chapter is in two parts. Part 1 discusses the ‘workability’ of metals and alloys and the hot deformation characteristics of Al–Li alloys, leading to the concept of Process Maps. A comprehensive Process Map for a binary Al–Li alloy illustrates the usefulness of these Maps for defining temperature–strain rate regions for safe and unsafe hot working, recrystallization and recovery, and superplastic behaviour Part 2 provides some general considerations about processing Al–Li alloy products, followed by a review and discussion of the currently available information for 3rd generation alloys. It is concluded that their complex TMP schedules may make it difficult to obtain optimum combinations of properties for thicker products.
Aluminum-Lithium Alloys
The material and manufacturing property requirements for selection and application of 3rd generation aluminium-lithium (Al–Li) alloys in aircraft and spacecraft are discussed. Modern structural concepts using Laser Beam Welding (LBW), Friction Stir Welding (FSW), SuperPlastic Forming (SPF) and selective reinforcement by Fibre Metal Laminates (FMLs) are also considered. Al–Li alloys have to compete with conventional aluminium alloys, Carbon Fibre Reinforced Plastics (CFRPs) and GLAss REinforced FMLs (GLARE), particularly for transport aircraft structures. Thus all these materials are compared before discussing their selection for aircraft. This is followed by a review of the aluminium alloy selection process for spacecraft. Actual and potential applications of 3rd generation Al–Li alloys are presented. For aircraft it is concluded that the competition between different material classes (aluminium alloys, CFRPs and FMLs) has reached a development stage where hybrid structures, using different types of materials, may become the rule rather than the exception. However, aluminium alloys are still the main contenders for spacecraft liquid propellant launchers.
Aluminum-Lithium Alloys
Aluminum–Lithium Alloys: Process Metallurgy, Physical Metallurgy, and Welding provides theoretical foundations of the technological processes for melting, casting, forming, heat treatment, and welding of Al–Li alloys. It contains a critical survey of the research in the field and presents data on commercial Al–Li alloys, their phase composition, microstructure, and heat treatment of the ingots, sheets, forgings, and welds of Al–Li alloys. It details oxidation kinetics, protective alloying, hydrogen in Al–Li alloys, and crack susceptibility. It also discusses grain structure and solidification, as well as structural and mechanical properties. The book is illustrated with examples of...
Aluminum-Lithium Alloys
This chapter describes the development of crystallographic texture and its effects on mechanical properties in aluminum-lithium alloys. Crystallographic texture evolves during the forming of wrought products from cast ingots of Al-Li alloys and consequently affects the mechanical properties. Practical approaches to control the texture have been developed and have been successfully used in the products obtained from industrial-scale ingots. This texture tailoring has significantly reduced the yield strength anisotropy. In addition, theoretical approaches have been used to model the yield strength anisotropy of aluminum alloys in the presence of complex precipitates.
Aluminum-Lithium Alloys
This chapter reviews the precipitation and precipitate phases that occur during heat treatments in multi-component Al-Li based alloys. It describes aspects related to nucleation, growth, morphology and orientation relationships of the strengthening precipitates δ’ and T1, the toughening precipitate S’ and the recrystallisation-inhibiting precipitate β’. Equilibrium precipitate phases such as T2, which are deleterious to the mechanical and corrosion properties of the alloys, are also described. It is shown that careful alloy chemistry control, two-step homogenization and controlled stretching prior to ageing can be employed to improve the volume fraction and distribution of the precipitate phases. All these processing aspects are necessary to achieve optimum combinations of properties for the alloys.
Aluminum-Lithium Alloys
The emergence of Al–Li alloys as potential light metal, for safe use in a spectrum of aircraft structures and related aerospace applications has in recent years engendered an unprecedented widespread interest aimed at studying, understanding and improving their mechanical properties. In this chapter, we present and discuss some of the key aspects relevant to aluminum-lithium alloys, spanning the specific domain of precipitation kinetics as influenced by composition and heat treatment, intrinsic microstructural features and their effects, the fundamental mechanisms contributing to strength, ductility, fracture toughness, and overall anisotropy in mechanical properties of these alloys. The tensile behavior of representative first generation, second generation and third generation aluminum-lithium alloys is also presented and briefly discussed. Microstructural influences on mechanical properties are examined with specific reference to matrix microstructural features, dislocation-microstructural feature interaction, and matrix slip characteristics.
