Deformation behaviour of Al–Cu–Li alloy containing T1 precipitates (original) (raw)
Related papers
Materials Science and Engineering: A, 2014
This paper presents a systematic study of the influence of the state of precipitation on the plasticity of an Al-Cu-Li alloy. By varying the heat treatment, a variety of T 1 precipitate morphologies are obtained. Atomic resolution electron microscopy observations show that T 1 precipitates remain shearable even during early stages of over-ageing when their thickness is of several nanometres. They appear to be sheared only by single dislocations at a given location, which prevents catastrophic strain localisation at a microscopic scale. In later stages of over-ageing, the study of macroscopic strain hardening rate and of slip line localisation strongly suggests a transition to precipitate by-passing. The influence of the strengthening mechanism on strain reversal experiments (Bauschinger effect) is discussed.
Materials Science Forum, 2008
Equal channel angular extrusion (ECAE), involving intense plastic straining under high applied pressure is generally recognized and extensively studied top down approach for producing bulk ultra-fine grained (UFG) metallic materials, and even going down in size to the nanometer range. In this research efforts are made to identify conditional under which grains with size less than 100 nm form after ECAE. Evolution of microstructure of Al-Li based alloy processed by ECAE is analyzed using transmission electron microscopy (TEM). Observations on the effect of precipitates/second phase particles in the sample on the deformation characteristics and their role on the increased degree of grain fragmentation process is highlighted. Samples of Al-Li based alloy are solutionized, quenched and aged at different temperatures to obtain well formed precipitate laths/plates before subjecting to ECAE. During the deformation process these precipitates disintegrate into fragments and get dispersed into the Al matrix. The fragments of a few nanometers size bring about drastic changes in the flow as well as the recovery characteristics of processed samples. Evidence for dynamic recrystallisation taking place during the ECAE processing is presented. It was observed that optimal thermal treatment leads to more effective grain refinement and consequently an ultra-fine grained microstructure could be achieved even after single pass in Al-Li based alloy containing precipitates and second phase particles.
2001
The role of plastic deformation prior to arti®cial aging on the microstructural evolution and mechanical properties of a novel Al± Li±Cu±X alloy designated AF/C 458 was investigated. Induced plastic deformation ranged from a non-stretched or 0% stretch condition to an 8% stretch, with intermediate stretches of 2%, 4% and 6%. Tensile properties, fractography and quantitative precipitate analysis were acquired from specimens that were water quenched from a solution heat treatment, immediately stretched and arti®cially aged at 150°C. Fractography was investigated through scanning electron microscopy (SEM). Quantitative transmission electron microscopy (TEM) determined the variation in precipitate type, number density, size and volume fraction of the major strengthening precipitates Age hardening curves for each level of mechanical stretch illustrated the enhanced aging kinetics of plastically deformed material. Quantitative TEM indicated that increasing amounts of pre-age stretch were found to greatly aect the competitive precipitation kinetics of T 1 and h HH ah H in AF/C 458 augmenting the volume fraction of ®ne matrix T 1 plates and dramatically decreasing the volume fraction of h HH ah H for isochronal treatments. A quantitative microstructural comparison of specimens exhibiting a given strength demonstrated that the imposed level of cold work dictated the density, size and volume fraction of the competing precipitates. The tensile data indicated a trend of increasing ductility for equivalent yield strengths with the increasing amount of pre-age mechanical stretch and therefore shorter arti®cial aging times. The quantitative precipitate data were used with a computer simulation for yield strength determination. The theoretical simulation reported calculated yield strengths in good accord with experimental results and can thus be used to predict the optimum microstructural con®guration for high strength. Ó
Materials Science and Engineering: A, 2015
The effect of grain microstructure on the age-hardening behavior is investigated on recrystallized and un-recrystallized Al-Cu-Li alloys by combining electron-backscatter-diffraction and micro-hardness mapping. The spatial heterogeneity of micro-hardness is found to be strongly dependent on the grain microstructure. Controlled experiments are carried out to change the pre-strain before artificial ageing. These experiments lead to an evaluation of the range of local strain induced by pre-stretching as a function of the grain microstructure and results in heterogeneous formation of the hardening T 1 precipitates.
Metals
The mechanical properties and microstructure evolution of an Al-Cu-Li alloy sheet processed via hot rolling (HR) (at 400 °C and 500 °C) or cryorolling (CR) (at −100 °C and −190 °C) and subsequence aging at 160 °C for 10 h were investigated. Before aging, the highest ultimate tensile strength of 502 MPa was achieved when the sheets were cryorolled at −190 °C, while the better ultimate tensile strength of 476 MPa and the best elongation rate of 11.1% was achieved simultaneously when the sheets were cryorolled at −100 °C. The refined grains and numerous uniform deformation-induced dislocations microstructures were responsible for the improved strength and enhanced ductility of the cryorolled sheets compared to that of the alloy processed by hot rolling with a low dislocation density zone (LDDZ) and high dislocation density zone (HDDZ). After aging at 160 °C for 10 h, the ultimate tensile strength further improved resulted from the greater precipitation strengthening, and the increased ...
Al3(Sc,Zr)-based precipitates in Al–Mg alloy: Effect of severe deformation
Acta Materialia, 2017
Precipitate evolution in an AA5024 Al-based alloy containing Sc and Zr is investigated in different states: as-cast, extruded and severely deformed. An overview of the microstructure is given and the evolution of particle size and morphology as a function of mechano-thermal processing is investigated, with an emphasis on the Al 3 (Sc,Zr)-based precipitates. The precipitates are found to maintain their coherence with the matrix after the interaction with dislocations and low-angle grain boundaries as it is revealed by atomistic simulations and by the so-called Geometric Phase Analysis of the local strain fields. It is established that the precipitates can loose their coherency with the matrix during the severe plastic deformation, that decreases generally grain boundary pinning effect and promotes recrystallization.
Textures and Microstructures, 1995
The influence of the initial grain size prior to deformation on the rolling and recrystallization textures is investigated in the alloy Al-l.8wt%Cu by X-ray macrotexture analysis. Two different particle stages are examined: (i) Small shearable precipitates give rise to shear band formation and, during annealing, to nucleation of recrystallization at shear bands. (ii) Large particles cause particle stimulated nucleation of recrystallization (PSN). The microstructural evolution, particularly during recrystallization nucleation, is elucidated by metallographical investigations supported by EBSD local texture analysis.Both the initial grain size and the precipitation state strongly influence the evolution of the rolling textures. The results are interpreted with the help of Taylor-type deformation models. The recrystallization textures of Al-alloys emerge from a superposition of the orientations stemming from the various nucleation sites, i.e. Cube-bands, shear bands and particles. An i...
13th International Conference on Aluminum Alloys, 2012
The use of aluminum-lithium alloys in aerospace applications requires a thorough knowledge of how processing and product geometry impact their microstructure, texture and mechanical properties. As with other aluminum alloys, anisotropy of mechanical properties has been related to the formation of deformation textures during thermo-mechanical processes. Static mechanical properties and microstructural characteristics such as texture and precipitate distribution were analysed in two series of 2099-T83 extrusions, i.e. a cylindrical extrusion and an integrally stiffened panel (ISP). The cylindrical extrusions present <111> and <100> fiber textures while the ISP possesses the same fiber textures with lower intensities. Rolling textures such as Brass were also observed in some locations of the ISP. The levels of longitudinal strength and static anisotropy correlate well with the intensity of the fiber texture. Moreover, varying densities of T 1 (Al 2 CuLi) precipitates were observed in the TEM.
Linking mechanical properties to precipitate microstructure in three Al-Mg-Si(-Cu) alloys
Materials Science and Engineering: A, 2021
The mechanical properties of age hardenable Al alloys depend strongly on the precipitate microstructure. This work has investigated the relationship between properties such as strength and ductility and the distribution of precipitates, using three Al-Mg-Si(-Cu) alloys (Cu≲0.1 at.%). A range of ageing conditions was examined in order to understand the effect of an evolving precipitate microstructure, and the results were used as input for strengthening models. The mechanical properties were obtained by tensile tests and microstructure characterisation was attained by transmission electron microscopy. The results showed that minor changes to the Si, Mg, and Cu additionsthe total addition (at.%) kept approximately equalhad a significant impact on material properties, with corresponding changes in the precipitate microstructure. On the peak strength plateaus differences as large as 35 MPa in yield strength were measured between the strongest and the weakest alloy, obtained as 410 MPa and 375 MPa, respectively. Higher material yield strength correlated well with a refined precipitate microstructure comprising higher number densities of smaller precipitates. Differences with respect to material ductility first appeared after moderate overageing of the alloys, showing negative correlation with material strength. At significantly overaged conditions the differences in strength exceeded 100 MPa, demonstrating large differences with respect to the thermal stability of these materials, which has important consequences for alloys exposed to elevated temperatures under in-service conditions. The highly comprehensive body of data presented here should serve as a valuable reference in the development of precipitation and strengthening models for the Al-Mg-Si-Cu system and will hopefully incite further investigations on the topics covered.
Computational Materials Science, 2014
In this study the influence of precipitates on the mechanical properties and plastic anisotropy of an age hardenable aluminum alloy during uniaxial loading was investigated using crystal plasticity modeling. The kinetics model of Myhr et al. was used to obtain the solute and precipitate features after different cycles of aging treatment. The amounts of solute, precipitate size and volume fraction, and dislocation density varying during deformation, were used to calculate the slip system strength. An explicit term was obtained based on the elastic inclusion model for the directional dependency of internal stress developed by non-shearable rod shape precipitates. Also, a dislocation evolution model was modified to assess the anisotropic influence of non-shearable precipitate on work hardening, and the effects of solute content on the rate of dynamic recovery. It was found that the model results were in good agreement with experimental uniaxial flow stress obtained under different aging conditions. The application of the model to single crystal revealed that the precipitates can reduce crystallography anisotropy, which in part was attributed to the precipitate induced anisotropy.