Journal of Microscopy, Vol. 255, Issue 3 2014, pp. 128–137
doi: 10.1111/jmi.12143
Received 30 December 2013; accepted 7 May 2014
Microscopy and microanalysis of complex nanosized strengthening precipitates in new generation commercial Al–Cu–Li alloys M . J . - F . G U I N E L ∗ , N . B R O D U S C H †, G . S H A ‡, M . A . S H A N D I Z †, H . D E M E R S †, M . T R U D E A U §, S.P. RINGER‡ & R. GAUVIN† ∗ Departments of Chemistry and Physics, College of Natural Sciences, University of Puerto Rico, San Juan, Puerto Rico
†Department of Mining and Materials Engineering, McGill University, Montr´eal, Qu´ebec, Canada ‡Australian Centre for Microscopy and Microanalysis, School of Aerospace, Mechanical and Mechatronic Engineering, University of Sydney, Sydney, NSW, Australia §Materials Science, Institut de Recherche d’Hydro-Qu´ebec, Varennes, Qu´ebec, Canada
Key words. Atom probe tomography, detection limit, electron energy-loss spectroscopy (EELS), electron microscopy, Monte Carlo simulations, X-ray energy-dispersive spectrometry (XEDS).
Summary Precipitates (ppts) in new generation aluminum–lithium alloys (AA2099 and AA2199) were characterised using scanning and transmission electron microscopy and atom probe tomography. Results obtained on the following ppts are reported: Guinier–Preston zones, T1 (Al2 CuLi), β’ (Al3 Zr) and δ’ (Al3 Li). The focus was placed on their composition and the presence of minor elements. X-ray energy-dispersive spectrometry in the electron microscopes and mass spectrometry in the atom probe microscope showed that T1 ppts were enriched in zinc (Zn) and magnesium up to about 1.9 and 3.5 at.%, respectively. A concentration of 2.5 at.% Zn in the δ’ ppts was also measured. Unlike Li and copper, Zn in the T1 ppts could not be detected using electron energy-loss spectroscopy in the transmission electron microscope because of its too low concentration and the small sizes of these ppts. Indeed, Monte Carlo simulations of EEL spectra for the Zn L2,3 edge showed that the signal-to-noise ratio was not high enough and that the detection limit was at least 2.5 at.%, depending on the probe current. Also, the simulation of X-ray spectra confirmed that the detection limit was exceeded for the Zn Kα X-ray line because the signal-to-noise ratio was high enough in that case, which is in agreement with our observations.
Introduction Advanced materials that offer high specific strengths for aircraft and aerospace industries applications are more than ever Correspondence to: Maxime Guinel, Departments of Chemistry and Physics, College of Natural Sciences, University of Puerto Rico, PO Box 70377, San Juan, Puerto Rico 00936-8377. Tel: 7873424013; fax: 7877644063; e-mail: [email protected]
needed because of the high fuel costs. Upgrading large and also seemingly small parts can significantly contribute to the reduction of the operating costs by saving weight. Aluminum (13 Al) is a material of choice because of its low density (2.7 g cm−3 ) combined with its ability to resist corrosion and its plentiness. In the mid-1920s, lithium (Li) was added to Al to provide further weight savings giving birth to the first generation of Al–Li alloys. With each 1 wt.% Li addition, the alloy density is reduced by about 3% and the stiffness (Young’s elastic modulus) is increased by about 6% (Rioja & Liu, 2012). However, these alloys found limited applications due to their anisotropic properties, low toughness and poor corrosion resistance. Other alloying elements were added in the second and third generations enabling the formation of potent strengthening precipitates (ppts). For example, the two alloys AA2099 and AA2199 recently commercialized by ALCOA Inc. (ALCOA Technical Center, Pittsburgh, PA, USA), are the results of these continuous improvements (Rioja & Liu, 2012). These two alloys were the basis of this study and their elemental compositions are listed in Table 1 (Giummarra et al., 2007). In these alloys, in addition to Li and copper (Cu), minor elements like magnesium (Mg), zinc (Zn) and manganese (Mn) enable the formation of potent nanosized strengthening ppts during thermal treatments. Despite growing commercial interests, only few published scientific studies addressed general microstructural characterization of these precipitation phases (Ma et al., 2011; Brodusch et al., 2012). Scanning and transmission electron microscopy (SEM and TEM, respectively) studies have shown the importance of precipitation for increasing strength and ductility of Al–Li–Cu alloys processed by severe plastic deformation (Munoz-Morris & Morris, 2010). The high strength and hardness are mostly attributed to the precipitation of the T1 ppts (Al2 CuLi) in the form of very thin platelets. TEM imaging and modelling C 2014 The Authors C 2014 Royal Microscopical Society Journal of Microscopy
MICROSCOPY AND MICROANALYSIS OF COMPLEX
Table 1. Elemental compositions (wt.%) of the AA2099 and AA2199 alloys (after Giummarra et. al., 2007).
Cu Li Zn Mg Mn Zr Fe Si Al
AA2099
AA2199
2.4–3.0 1.6–2.0 0.4–1.0 0.1–0.5 0.1–0.5 0.05–0.12
doi: 10.1111/jmi.12143
Received 30 December 2013; accepted 7 May 2014
Microscopy and microanalysis of complex nanosized strengthening precipitates in new generation commercial Al–Cu–Li alloys M . J . - F . G U I N E L ∗ , N . B R O D U S C H †, G . S H A ‡, M . A . S H A N D I Z †, H . D E M E R S †, M . T R U D E A U §, S.P. RINGER‡ & R. GAUVIN† ∗ Departments of Chemistry and Physics, College of Natural Sciences, University of Puerto Rico, San Juan, Puerto Rico
†Department of Mining and Materials Engineering, McGill University, Montr´eal, Qu´ebec, Canada ‡Australian Centre for Microscopy and Microanalysis, School of Aerospace, Mechanical and Mechatronic Engineering, University of Sydney, Sydney, NSW, Australia §Materials Science, Institut de Recherche d’Hydro-Qu´ebec, Varennes, Qu´ebec, Canada
Key words. Atom probe tomography, detection limit, electron energy-loss spectroscopy (EELS), electron microscopy, Monte Carlo simulations, X-ray energy-dispersive spectrometry (XEDS).
Summary Precipitates (ppts) in new generation aluminum–lithium alloys (AA2099 and AA2199) were characterised using scanning and transmission electron microscopy and atom probe tomography. Results obtained on the following ppts are reported: Guinier–Preston zones, T1 (Al2 CuLi), β’ (Al3 Zr) and δ’ (Al3 Li). The focus was placed on their composition and the presence of minor elements. X-ray energy-dispersive spectrometry in the electron microscopes and mass spectrometry in the atom probe microscope showed that T1 ppts were enriched in zinc (Zn) and magnesium up to about 1.9 and 3.5 at.%, respectively. A concentration of 2.5 at.% Zn in the δ’ ppts was also measured. Unlike Li and copper, Zn in the T1 ppts could not be detected using electron energy-loss spectroscopy in the transmission electron microscope because of its too low concentration and the small sizes of these ppts. Indeed, Monte Carlo simulations of EEL spectra for the Zn L2,3 edge showed that the signal-to-noise ratio was not high enough and that the detection limit was at least 2.5 at.%, depending on the probe current. Also, the simulation of X-ray spectra confirmed that the detection limit was exceeded for the Zn Kα X-ray line because the signal-to-noise ratio was high enough in that case, which is in agreement with our observations.
Introduction Advanced materials that offer high specific strengths for aircraft and aerospace industries applications are more than ever Correspondence to: Maxime Guinel, Departments of Chemistry and Physics, College of Natural Sciences, University of Puerto Rico, PO Box 70377, San Juan, Puerto Rico 00936-8377. Tel: 7873424013; fax: 7877644063; e-mail: [email protected]
needed because of the high fuel costs. Upgrading large and also seemingly small parts can significantly contribute to the reduction of the operating costs by saving weight. Aluminum (13 Al) is a material of choice because of its low density (2.7 g cm−3 ) combined with its ability to resist corrosion and its plentiness. In the mid-1920s, lithium (Li) was added to Al to provide further weight savings giving birth to the first generation of Al–Li alloys. With each 1 wt.% Li addition, the alloy density is reduced by about 3% and the stiffness (Young’s elastic modulus) is increased by about 6% (Rioja & Liu, 2012). However, these alloys found limited applications due to their anisotropic properties, low toughness and poor corrosion resistance. Other alloying elements were added in the second and third generations enabling the formation of potent strengthening precipitates (ppts). For example, the two alloys AA2099 and AA2199 recently commercialized by ALCOA Inc. (ALCOA Technical Center, Pittsburgh, PA, USA), are the results of these continuous improvements (Rioja & Liu, 2012). These two alloys were the basis of this study and their elemental compositions are listed in Table 1 (Giummarra et al., 2007). In these alloys, in addition to Li and copper (Cu), minor elements like magnesium (Mg), zinc (Zn) and manganese (Mn) enable the formation of potent nanosized strengthening ppts during thermal treatments. Despite growing commercial interests, only few published scientific studies addressed general microstructural characterization of these precipitation phases (Ma et al., 2011; Brodusch et al., 2012). Scanning and transmission electron microscopy (SEM and TEM, respectively) studies have shown the importance of precipitation for increasing strength and ductility of Al–Li–Cu alloys processed by severe plastic deformation (Munoz-Morris & Morris, 2010). The high strength and hardness are mostly attributed to the precipitation of the T1 ppts (Al2 CuLi) in the form of very thin platelets. TEM imaging and modelling C 2014 The Authors C 2014 Royal Microscopical Society Journal of Microscopy
MICROSCOPY AND MICROANALYSIS OF COMPLEX
Table 1. Elemental compositions (wt.%) of the AA2099 and AA2199 alloys (after Giummarra et. al., 2007).
Cu Li Zn Mg Mn Zr Fe Si Al
AA2099
AA2199
2.4–3.0 1.6–2.0 0.4–1.0 0.1–0.5 0.1–0.5 0.05–0.12
