Papers by Keyword: Al-Li

Abstract: 2195 Al-Li alloy is famous for high strength, excellent fatigue strength and good stress corrosion resistance, which is widely used in the manufacture of high-performance aerospace components. The aim of this study is to validate how the stress relaxation aging behavior effect on the mechanical properties of 2195 Al-Li alloy. Through mechanical property test, the research was found that the performance after stress relaxation aging is higher than artificial aging (AA). In addition, the analysis of scanning electron microscopy SEM and TEM revealed that dislocations should be introduced by the stress relaxation aging process, which is more conducive to the precipitation of the T1 phase and strengthened the material with prolong ageing time. The results show that stress relaxation aging can significantly promote the precipitation of the T1. Therefore, this paper sheds new light on how SRA can improve mechanical properties and that SRA make better improve the distribution of precipitates in the grain boundary.

Abstract: Al-Li alloys have higher mechanical properties and more lightweight than other conventional aluminum alloys. Therefore , it is focused as a good material for weight reduction of industrial fields. However, since the Al-Li alloy are highly active and hard to cast, there has been limited research on casting. In this study, age-hardening behavior of Al-2.5mass%Li alloys cast into sand and metal mold were investigated. All alloys cast into Y-block shape sand mold, and then artificial aged after solution treated at 743K for 36ks. Because of difference in quantity of precipitation by metastable δ’(Al₃Li) phase, peak hardness of metal mold casting is higher than that of sand molds castings.

Abstract: Three-phase secondary rectification spot welding machine had been adopted to join 5A90 Aluminum-lithium alloy with a thickness of 2 mm, at different welding conditions. The mechanical properties of the lap joints were investigated and microstructure were analyzed respectively. The results showed that the joint fabricated at a welding current of 45.5 kA, welding time of 4 cycles, and electrode pressure of 8.55 kN exhibited higher tensile-shear force value of 7.7 kN compared to the other joints. The nugget were mainly composed of equiaxial grains and cellular dendrites. Meanwhile, equiaxed zone can be divided into the equated dendrites, the wormlike eutectic structure and few equiaxed non-dendrites. The tensile fracture surfaces exhibited a hybrid ductile-brittle fracture, while Al3Li strengthening phase lied in the bottom of dimple.

Abstract: Al-Li alloys are characterized by a strong anisotropy in mechanical properties and microstructure with respect to the rolling direction. Plates of 2198 Al-Li alloy were friction stir welded by employing maximum rotation speed: 1000 rev/min and welding speed of 80 mm/min, both in parallel and orthogonal directions with respect to the rolling one. The joints mechanical properties were evaluated by means of tensile tests at room temperature. In addition, fatigue tests performed with a resonant electro-mechanical testing machine under constant amplitude control up to 250 Hz loading, were conducted in axial control mode with R(σmin/σmax)=0.33, for all the welding and rotating speed conditions. The fatigue crack propagation experiments were performed by employing single edge notched specimens.With the aim to characterize the weld performances, both the microstructure evolution at jointed cross sections, related to the welding variables, and the fractured surfaces were respectively analyzed by means of optical and scanning electron microscopy.

Abstract: The effects of trace Ce, Ag on the microstructure and mechanical properties of Al-Cu-Li alloy after thermal exposure have been investigated. It’s found that the addition of Ce may lead to a slight increase in mechanical properties after thermal exposure at 107  . The stability of T1 phase is enhanced by independent Ag addition and the combined additions of Ag and Ce,which results in higher strength compared with Ag-free alloy at 150  thermal exposure. However, at 200  exposure, a great number of q¢ precipitates at the expense of T1 may be responsible for higher tensile strength in the Ag-free alloy than that of the independent addition of Ag and combined additions of Ag and Ce alloys.

Abstract: The hot deformation behaviors and microstructure in Al-Cu-Li alloy containing small amount of Ag and Mg were investigated by transmission electron microscopy and isothermal compression tests.When the strain rate is 0.1, 0.01 and 0.001s-1(the deformation temperature within the range of 360-520􀀀 ) and 1 s-1(deformation temperature 520 􀀀 )respectively, the flow stress decreases after a peak value, showing dynamic recrystallization,while the steady-state flow characteristics exist on the other deformation conditions. The flow stress of Al-Cu-Li-Mg-Ag alloy during hot deformation can be expressed by a Zener-Hollomon parameter in the hyperbolic-sine function with the hot deformation activation energyDH of 250.45kJ/mol. The dislocations may climb with support from many vacancies generated during hot deformation, thus forming lots of helical dislocations. The dynamic precipitation and successive dynamic particles coarsening during hot compression have been assumed to be responsible for further flow softening when deformed at low strain rates.

Abstract: For 2195-T8 plate, design properties are based on the mechanical properties at the near surface location, corresponding to the load carrying thin membrane location in machined integrally stiffened structure. Mechanical properties at the near surface location are lower than those at the t/4 and t/2 locations. This work examined the effect of alternate temper and hot rolling practices on near surface strength levels. Results showed that alternate hot rolling practice were very effective in raising near surface strengths and improving property uniformity, and were well correlated with crystallographic texture measurements.

Abstract: Crack turning or delamination behavior of AA 2050-T87 and AA 7050-T7451 ESE(T) and hourglass coupons under cyclic fatigue conditions is presented. Fatigue crack growth rate curves, fracture surface examinations, and the preferred manner of crack growth for each alloy are discussed in an effort to better understand fatigue crack growth behavior of aluminum-lithium alloys in structural components under service conditions.

Abstract: Alcoa has made a fundamental shift in its aerospace R&D program, broadening its scientific and engineering portfolio by creating an integrated, strategic, long-term initiative. The ultimate goal is to help re-define the future performance, cost and value of the metallic and hybrid aerostructures that the company feels will be required to meet the mission requirements of tomorrow’s aircraft. Having intensely studied various structural options, Alcoa believes Hybrid Structural Assembly optimized with a combination of Advanced Aluminum and Hybrid Components offer the best opportunities to maximize structural performance. Not only do the new alloys, notably 3rd Generation Al-Li alloys and high strength and high toughness 7xxx alloys provide structural performance enhancements, they also offer dramatic improvements in corrosion resistance. In this paper, several advanced alloys and structural concepts targeted for next generation wing and fuselage applications and large scale test article results supporting Alcoa’s optimism for Advanced Metallic and Hybrid Structures are reviewed.