Hot deformation characterization of as-homogenized Al-Cu-Li X2A66 alloy through processing maps and microstructural evolution

doi:10.1016/j.jmst.2019.06.001

Abstract

Abstract:

Uniaxial compression tests were carried out on an Al-Cu-Li alloy at a temperature range of 300-500°C and a strain rate range of 0.001-10 s^-1. Four representative instability maps based on Gegel, Alexander-Malas (A-M), Kumar-Prasad (K-P) and Murty-Rao (M-R) criteria were constructed. Through formula deduction and microstructural observation, it can be concluded that M-R criterion is more accurate than K-P criterion, and the first two criteria are better than Gegel and A-M criteria. From a power dissipation map and a M-R instability map, the optimized processing parameters are 480-500°C/0.001-0.1 s^-1 and 420-480°C/0.1-1 s^-1. The corresponding microstructural analysis shows that dynamic recovery and partial dynamic recrystallization are main dynamic softening mechanisms. Transmission electron microscopy observation indicated that a large number of primary coarse T₁ (Al₂CuLi) particles precipitated in the homogenized specimen. After deformation at 500°C, most of the primary T₁ particles dissolved back into the matrix, and secondary fine T₁ particles precipitated at deformation-induced dislocations, high angle grain boundaries and other dispersed particles.

Key words: Al-Cu-Li alloy, Hot deformation, Processing map, Dynamic recrystallization, Precipitate

Liwei Zhong, Wenli Gao, Zhaohui Feng, Zheng Lu, Congcong Zhu. Hot deformation characterization of as-homogenized Al-Cu-Li X2A66 alloy through processing maps and microstructural evolution[J]. J. Mater. Sci. Technol., 2019, 35(10): 2409-2421.

Figures/Tables 15

Table 1 Chemical composition of the experimental X2A66 alloy (wt%).

Cu	Li	Mg	Zn	Mn	Zr	Fe	Si	Ti	Al
3.63	1.34	0.39	0.64	0.31	0.12	<0.10	<0.05	<0.10	Bal.

Fig. 1. True stress-true strain curves of X2A66 alloy at different temperatures with strain rates of (a) 0.001 s-1, (b) 0.01 s-1, (c) 0.1 s-1, (d) 1 s-1, and (e) 10 s-1.

Fig. 2. Variation of peak flow stresses of X2A66 alloy at different temperatures and strain rates.

Fig. 3. Relationship between flow stress and strain rate with the strains of (a) 0.3, (b) 0.4, (c) 0.5, and (d) 0.65.

Fig. 4. 3D strain rate sensitivity map (a) and power dissipation map (b) for the studied X2A66 alloy.

Fig. 5. Instability maps established as per the second inequalities of Gegel’s and A-M’ s criteria at a strain of 0.65.

Fig. 6. Instability map constructed based on A-M criterion at a strain of 0.65.

Fig. 7. Instability maps established as per (a) K-P and (b) M-R instability criteria at a strain of 0.65.

Fig. 8. Comparison of instability maps plotted at a strain of 0.65 based on the A-M and M-R criteria.

Fig. 9. Microstructures of as-homogenized X2A66 alloy: (a) EBSD micrograph; (b) XRD pattern; (c) BF TEM image; (d) SAED pattern along [112]Al zone axis of lath-shaped phase; (e) SAED pattern along [112]Al zone axis of spherical particle; (f) SAED pattern along [010]Al zone axis of blocky particle.

Fig. 10. Optical micrographs of alloy X2A66 deformed at the strain of 0.7 with different temperatures and strain rates.

Fig. 11. Grain boundary maps of X2A66 alloy compressed at 500°C and 0.01 s-1 with different strains: (a) 0.1; (b) 0.4; (c) 0.7; (d) 1.2.

Fig. 12. Misorientation distribution plots of X2A66 alloy compressed at 500°C and 0.01 s-1 with different strains: (a) 0.1; (b) 0.4; (c) 0.7; (d) 1.2.

Fig. 13. TEM micrographs of X2A66 alloy deformed at the strain rate of 0.01 s-1 with different temperatures: (a, b) 300°C; (c, d) 420°C; (e, f) 500°C.

Fig. 14. Microstructures of X2A66 alloy deformed at 500°C and 0.01 s-1: (a) T1 phase on dislocations; (b) T1 phase on grain boundary and dispersed particles; (c, d) HAADF-STEM images showing the T1 particles before and after compression, respectively.

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