Enhanced age-hardening behavior in Al-Cu alloys induced by in-situ synthesized TiC nanoparticles

doi:10.1016/j.jmst.2018.09.029

Abstract

Abstract:

The influence of in-situ synthesized TiC nanoparticles on age-hardening behavior of Al-Cu alloys was investigated in Al-4.5Cu-1.5TiC alloy. It was found that TiC nanoparticles decrease the peak-age time effectively, from about 20?h for Al-4.5Cu alloy decreasing to about 12?h for the Al-4.5Cu-1.5TiC. Mechanical property test shows that the age-hardening effect has been improved by the TiC nanoparticles. The increment of yield strength before and after aging is about 84?MPa for Al-4.5Cu, while, it reaches to about 113?MPa for the Al-4.5Cu-1.5TiC. After aging heat treatment, precipitates have been observed both in matrix and around TiC nanoparticles. Due to the difference of coefficient of thermal expansion between TiC and Al, high density dislocations in the Al-4.5Cu-1.5TiC were generated during water quenching after solution. Dislocations play a role of diffusion path for Cu atoms during aging, which reduces the peak-age time. Alpha-Al lattice distortion resulted from lattice mismatch of TiC/Al interface induces the precipitation of θ? phase around TiC nanoparticles, which increases the number density of θ? and improves the age-hardening effect. This finding is supposed to be also applicable to alloy systems of Al-Cu-Mg, Al-Cu-Mg-Li, Al-Cu-Mg-Ag, etc.

Key words: Al-Cu alloy, TiC nanoparticles, θ? precipitation;, Age-hardening, Mechanical property

Huabing Yang, Tong Gao, Huaning Zhang, Jinfeng Nie, Xiangfa Liu. Enhanced age-hardening behavior in Al-Cu alloys induced by in-situ synthesized TiC nanoparticles[J]. J. Mater. Sci. Technol., 2019, 35(3): 374-382.

Figures/Tables 14

Fig. 1. XRD patterns of Al-4.5Cu and Al-4.5Cu-1.5TiC alloys: (a) as-cast; (b) after solution at 520?°C for 24?h and water quenching.

Fig. 2. (a) Microstructure of the Al-4.5Cu-1.5TiC alloy after solution heat treatment, the inset shows the magnified image of the squired area; (b) high magnification microstructure of the Al-4.5Cu-1.5TiC; (c, d) EDS mapping analysis for Fig. 2(a); (e) EDS analysis for the point in Fig. 2(b); (f) TEM image of microstructure for the Al-4.5Cu-1.5TiC alloy, the inset shows the selected area electron diffraction (SAED) analysis for TiC nanoparticles.

Fig. 3. (a) SEM image of extracted TiC particles; (b) EDS analysis for the point in Fig. 3(a); (c) TEM image of the extracted particles, the inset shows lattice fringe of the squared area; (d) selected area electron diffraction (SAED) analysis for the extracted particles.

Fig. 4. (a, d) TEM images of microstructure for the Al-4.5Cu-1.5TiC alloy after solution heat treatment, showing TiC particles in matrix; (b, e) HRTEM images of area①and③respectively; (c, f) inverse fast fourier transform (IFFT) images of area②and④, respectively.

Fig. 5. Brinell hardness of the Al-4.5Cu and Al-4.5Cu-1.5TiC alloys as a function of aging time at 180?°C, both alloys have been solution heat treated before aging.

Fig. 6. DSC curves of the Al-4.5Cu and Al-4.5Cu-1.5TiC alloys after solution heat treatment.

Table 1 Parameters from the DSC curves in Fig. 6.

	GP zones		θ?
Alloys	Starting temperature (°C)	Finish temperature (°C)	Starting temperature (°C)	Finish temperature (℃)
Al-4.5Cu	128	203	236	422
Al-4.5Cu-1.5TiC	124	174	201	352

Fig. 7. TEM images of θ? precipitate in the matrix of peak-aged (a) Al-4.5Cu and (b, c) Al-4.5Cu-1.5TiC alloys. (d, e) low and high magnified TEM images for the Al-4.5Cu-1.5TiC alloy, showing the precipitate around TiC particle; (f) selected area electron diffraction (SAED) pattern for the TiC particle in Fig. 7(d).

Fig. 8. (a) Diagrams for the shrink of TiC and α-Al during cooling from elevated temperature to room temperature and corresponding stress; (b) diagrams for the interface between TiC and α-Al, showing the lattice mismatch and distortion.

Fig. 9. TEM images of typical dislocation structures for the (a) Al-4.5Cu-1.5TiC and (b) Al-4.5Cu alloys with 520?°C, 24?h solution heat treatment; (c-e) dislocations in the Al-4.5Cu-1.5TiC and corresponding EDS mapping analysis of Al and Cu elements.

Fig. 10. (a) Engineering stress-strain curves for the solution and peak-aged Al-4.5Cu and Al-4.5Cu-1.5TiC alloys; (b) increment of yield strength before and after aging for the Al-4.5Cu and Al-4.5Cu-1.5TiC alloys.

Table 2 Mechanical properties of the Al-4.5Cu and Al-4.5Cu-1.5TiC alloys.

Alloys	Heat treatment	Ultimate tensile strength (MPa)	Yield strength (MPa)	Elongation (%)
Al-4.5Cu	Solution	261?±?11	151?±?6	9.9?±?0.5
Al-4.5Cu	Solution and aging	335?±?14	235?±?10	7.2?±?0.4
Al-4.5Cu-1.5TiC	Solution	346?±?12	189?±?7	13.8?±?0.6
Al-4.5Cu-1.5TiC	Solution and aging	412?±?15	302?±?11	10.1?±?0.4

Fig. 11. Fracture surface images for the peak-aged (a, b) Al-4.5Cu and (c, d) Al-4.5Cu-1.5TiC alloys after tensile test.

Fig. 12. Orowan strength as a function of particle size of reinforcement with reinforcement volume fraction set as 5%.

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