A high-strength, ductile Al-0.35Sc-0.2Zr alloy with good electrical conductivity strengthened by coherent nanosized-precipitates

Abstract

Abstract:

Ductility and electrical conductivity of metallic materials are inversely correlated with their strength, resulting in a difficulty of optimizing all three simultaneously. We design an Al-Sc-Zr-based alloy using semisolid extrusion to yield a good trade-off between strength and ductility along with excellent electrical conductivity. The Al-0.35Sc-0.2Zr wire with a diameter of 3?mm exhibited the best combined properties: a tensile strength of 210?±?2?MPa, elongation of 7.6%?±?0.5%, and an electrical conductivity of 34.9?±?0.05?MS/m. The average particle size of nanosized Al₃(Sc, Zr) precipitates increased from 6.5?±?0.5?nm to 25.0?±?0.5?nm as the aging time increased from 1?h to 96?h at 380?°C, accompanied by the corresponding volume fraction variation from (6.2?±?0.1)?×?10^-4 to (3.7?±?0.1)?×?10^-3. As proved by transmission electron microscopy observation, the high strength originates from the effective blockage of dislocation motion by numerous nanosized Al₃(Sc, Zr) precipitates whilst both electrical conductivity and ductility remain at a high level due to the coherent precipitates possessing an extremely low electrical resistivity.

Key words: Al-0.35Sc-0.2Zr alloy, Mechanical properties, Electrical conductivity, Nanosized precipitates

Guan Renguo,Shen Yongfeng,Zhao Zhanyong,Wang Xiang. A high-strength, ductile Al-0.35Sc-0.2Zr alloy with good electrical conductivity strengthened by coherent nanosized-precipitates[J]. J. Mater. Sci. Technol., 2017, 33(3): 215-223.

Figures/Tables 7

Table 1 Chemical composition of commercial pure Al used in this study (wt%).

Si	Fe	Cu	Mn	Mg	Zn	Ti	Al
≤0.20	≤0.25	≤0.04	≤0.03	≤0.03	≤0.04	≤0.03	≥99.7

Fig. 1. Effect of aging time on the tensile strength and electrical conductivity of Al-Sc-Zr alloys aged at 380?°C.

Fig. 2. Effect of aging time on the precipitates in Al-0.35Sc-0.2Zr alloys aged for (a) 1?h, (b) 12?h, (c) 48?h, and (d) 96?h at 380?°C; aged at 300?°C for 48?h (e) and 96?h (f), respectively. Labels A in (a) and B in (c) indicate the positions in which selected-area-electron-diffraction (SAED) analyses were performed, shown in (g) and (h).

Table 2 Effect of the aging time on the volume fraction and size of Al3(Sc, Zr) precipitates in the Al-0.35Sc-0.2Zr wire aged at 300 and 380?°C.

Aging		Al₃(Sc, Zr)
Temp. (°C)	Time (h)	Volume fraction, f_v	Diameter, d (nm)	Spacing, λ (nm)
300	48	(1.7?±?0.1)?×?10^-3	10?±?0.5	100
	96	(2.9?±?0.1)?×?10^-3	15?±?0.5	90
380	1	(6.2?±?0.1)?×?10^-4	6.5?±?0.5
	12	(1.5?±?0.1)?×?10^-3	13.0?±?0.5
	48	(3.1?±?0.1)?×?10^-3	21.0?±?0.8	130
	96	(3.7?±?0.1)?×?10^-3	25.0?±?1.0	110

Fig. 3. Effect of aging time on the tensile strength and elongation of the Al-0.35Sc-0.2Zr alloy aged at 380?°C.

Fig. 4. Evolution of the tensile strength and elongation (a), electrical conductivity (b) with the variations in the nominal diameter of the Al-0.35Sc-0.2Zr wires aged at 380?°C for different durations. After aged at 380?°C for 60?h, effect of nominal diameter on the tensile strength of the Al-0.35Sc-0.2Zr wires tested at different temperatures for 1?h (c).

Fig. 5. Pinning effect of the precipitates on the dislocations in the Al-0.35Sc-0.2Zr alloy aged at 380?°C for (a) 12?h, (b) 96?h. HRTEM images (c) and (d) showing a microtwin (A) and the stacking faults (SFs) (B, C) near the nanosized Al3(Sc, Zr) particle in the deformed Al-0.35Sc-0.2Zr alloy, which was aged at 380?°C for 12?h before tension. Close observations to areas indicated as A, B and C in (c) and (d) are shown as (e), (f) and (g), respectively.

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