Coarsening kinetics and strengthening mechanisms of core-shell nanoscale precipitates in Al-Li-Yb-Er-Sc-Zr alloy

doi:10.1016/j.jmst.2020.05.061

Abstract

Abstract:

The tailored nanoparticles with a complex core/shell structure can satisfy a variety of demands, such as lattice misfit, shearability and coarsening resistance. In this research, core-shell nanoscale Al₃(Yb, Er, Sc, Zr, Li) composite particles were precipitated in Al-2Li-0.1Yb-0.1Er-0.1Sc-0.1 Zr (wt%) alloy through the double-aging treatment, in which the core was (Yb, Er, Sc, Zr)-rich formed at 300 °C and the shell was Li-rich formed at 150 °C. The coarsening kinetics and precipitate size distributions (PSDs) of Al₃(Yb, Er, Sc, Zr, Li) particles aged at 150 °C previously aged at 300 °C for 24 h showed a better fit to the relation of <r>² ∝ kt and normal distribution, indicating that the coarsening of precipitates was controlled by interface reaction, not diffusion. The Orowan bypass strengthening was operative mechanism at 150 °C.

Key words: Al-Li alloys, Aging, Core-shell structure, Coarsening kinetics, Strengthening mechanisms

Yang Wang, Shun Zhang, Ruizhi Wu, Nodir Turakhodjaev, Legan Hou, Jinghuai Zhang, Sergey Betsofen. Coarsening kinetics and strengthening mechanisms of core-shell nanoscale precipitates in Al-Li-Yb-Er-Sc-Zr alloy[J]. J. Mater. Sci. Technol., 2021, 61: 197-203.

Figures/Tables 9

Fig. 1. Evolution of the microhardness for Al-Li-Yb-Er-Sc-Zr at isochronal aging in the stages of 50 °C /h.

Fig. 2. Evolution of the microhardness for Al-Li-Yb-Er-Sc-Zr at isothermal aging for 300 °C/0-144 h and 300 °C/24 h + 150 °C/96 h.

Fig. 3. (a) Dark-field TEM image of core-shell Al3(Yb, Er, Sc, Zr, Li) composite particles aged isothermally at 300 °C/24 h + 150 °C/144 h in Al-Li-Yb-Er-Sc-Zr and the inset selected area diffraction pattern in [001] zone axis. (b, c) HAADF-STEM of composite particles and corresponding element mapping distribution image of Yb, Er, Sc and Zr: (b) HAADF-STEM image; (c) element mapping distribution image.

Fig. 4. (a, b) HRTEM images of a core-shell Al3(Yb, Er, Sc, Zr, Li) composite composite particle aged isothermally at 300 °C/24 h + 150 °C/144 h in Al-Li-Yb-Er-Sc-Zr.

Fig. 5. The measured dark-field TEM images of Al3(Yb, Er, Sc, Zr, Li) composite particles at aged isothermally at 300 °C/24 h + 150 °C/48 h, 96 h and 144 h and the inset selected area diffraction pattern in [001] zone axis: (a) 48 h; (b) 96 h; (c) 144 h.

Fig. 6. Average radius, <r>, of core-shell Al3(Yb, Er, Sc, Zr, Li) particles as a function of isothermal aging at 150 °C previously aged at 300 °C for 24 h.

Fig. 7. PSDs of Al3(Yb, Er, Sc, Zr, Li) aging at 150 °C previously aged at 300 °C for 24 h: (a) 150 °C/48 h; (b) 150 °C/ 96 h; (c) 150 °C/144 h. The predictions of LSW theory (solid line) and Gaussian fitting (dotted line) are shown for comparison.

Fig. 8. Combined PSDs of Al3(Yb, Er, Sc, Zr, Li) for all times (48 h + 96 h + 144 h) at 150 °C. The predictions of LSW theory (solid line) and Gaussian fitting (dotted line) are shown for comparison.

Table 1 Experimental and calculated strength increments aged at 150 °C for 48 h, 96 h and 144 h previously aged at 300 °C for 24 h.

Aging Time	Δσ_ord (MPa)	Δσ_coh+Δσ_mod (MPa)	Δσ_Or (MPa)	ΔHV/3 (MPa)
48 h	95	109	243	220
96 h	109	138	234	237
144 h	122	162	239	230

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