Microstructure and properties of novel Al-Ce-Sc, Al-Ce-Y, Al-Ce-Zr and Al-Ce-Sc-Y alloy conductors processed by die casting, hot extrusion and cold drawing

doi:10.1016/j.jmst.2020.03.073

Abstract

Abstract:

In order to overcome the trade-off between the strength and electrical conductivity of aluminum alloy conductors, the new Al-Ce-Sc, Al-Ce-Y, Al-Ce-Zr and Al-Ce-Sc-Y alloys were prepared by die casting, high temperature homogenization treatment, hot extrusion and cold drawing. Adding Sc and Y eliminated the dendrite segregation of the as-cast Al-0.2Ce alloy and promoted the formation of equiaxed grains with the average grain size of 142.5 μm. The Al-0.2Ce-0.2Sc-0.1Y alloy inherited the great tensile properties of Al-0.2Ce-0.2Sc alloy and the high electrical conductivity of Al-0.2Ce-0.1Y alloy simultaneously. After cold drawing and annealing at 200 °C for 5 h, the ultimate tensile strength of Al-0.2Ce-0.2Sc-0.1Y alloy reached 200 MPa and 198 MPa, the elongation reached 6.8 % and 8.5 %, and the electrical conductivity reached 61.01 % and 61.77 %, respectively. The main second phase of Al-0.2Ce-0.2Sc-0.1Y alloy after hot extrusion were Al₁₃Fe₃Ce containing a few Y and Si atoms. The larger size and proportion of the second phase greatly reduced the concentration of solute Fe and Si atoms and the addition of Y significantly decreased the density of defects after cold drawing compared to Al-0.2Ce-0.2Sc alloy, which improved electrical conductivity of the alloy. Furthermore, the dispersed and coherent nano-size Al₃Sc precipitions of Al-0.2Ce-0.2Sc-0.1Y alloy greatly improved strength, elongation and heat resistance. Compared with Al-0.2Ce-0.2Sc alloy, the lower density of dislocation, stacking fault and subgrain boundary and the larger size of Al₃Sc precipitions with enrichment of Y atoms enable the Al-0.2Ce-0.2Sc-0.1Y alloy to maintain high strength, elongation and electrical conductivity after annealing.

Key words: Al-Ce-Sc-Y alloy, Electrical conductivity, Mechanical properties, Second phase, Nano-size precipitates

Weiyi Wang, Qinglin Pan, Geng Lin, Xiaoping Wang, Yuqiao Sun, Xiangdong Wang, Ji Ye, Yuanwei Sun, Yi Yu, Fuqing Jiang, Jun Li, Yaru Liu. Microstructure and properties of novel Al-Ce-Sc, Al-Ce-Y, Al-Ce-Zr and Al-Ce-Sc-Y alloy conductors processed by die casting, hot extrusion and cold drawing[J]. J. Mater. Sci. Technol., 2020, 58: 155-170.

Figures/Tables 16

Table 1 Chemical compositions of the studied alloys (wt%).

Alloys	Ce	Sc	Y	Zr	Fe	Si	Al
Al	—	—	—	—	0.17	0.082	Bal
Al-0.2Ce	0.18	—	—	—	0.14	0.074	Bal
Al-0.2Ce-0.2Sc	0.18	0.19	—	—	0.15	0.080	Bal
Al-0.2Ce-0.1Y	0.19	—	0.11	—	0.14	0.062	Bal
Al-0.2Ce-0.12 Zr	0.18	—	—	0.12	0.14	0.088	Bal
Al-0.2Ce-0.2Sc-0.1Y	0.19	0.20	0.11	—	0.14	0.064	Bal

Fig. 1. The performances of the studied alloys with different compositions and states: (a) hardness; (b) electrical conductivity; (c) engineering stress-engineering strain curves under cold drawing state; (d) engineering stress-engineering strain curves under annealing state; (e) the relationship between ultimate tensile strength and electrical conductivity.

Table 2 Mechanical properties and electrical conductivity with error values of the alloys after cold drawing and annealing.

Alloys and states		Hardness (HV)	Electrical conductivity (% IACS)	Ultimate tensile strength (MPa)	Yield strength (MPa)	Elongation (%)
Cold drawing	Al	40.3 ± 0.8	61.58 ± 0.20	132 ± 3	118 ± 2	4.4 ± 0.4
	Al-0.2Ce	41.1 ± 1.0	61.83 ± 0.12	138 ± 3	128 ± 1	5.2 ± 0.3
	Al-0.2Ce-0.2Sc	59.5 ± 1.0	60.45 ± 0.16	193 ± 2	176 ± 1	8.2 ± 0.5
	Al-0.2Ce-0.1Y	43.4 ± 0.8	62.02 ± 0.04	154 ± 2	132 ± 2	3.2 ± 0.2
	Al-0.2Ce-0.12 Zr	42.0 ± 0.5	58.46 ± 0.11	155 ± 2	138 ± 2	5.2 ± 0.3
	Al-0.2Ce-0.2Sc-0.1Y	57.6 ± 0.4	61.01 ± 0.14	200 ± 1	169 ± 1	6.8 ± 0.3
Annealing (200 °C/5 h)	Al	39.3 ± 0.8	62.03 ± 0.20	124 ± 3	110 ± 2	4.3 ± 0.3
	Al-0.2Ce	40.0 ± 0.7	62.18 ± 0.30	129 ± 2	108 ± 1	4.1 ± 0.3
	Al-0.2Ce-0.2Sc	58.6 ± 0.8	60.71 ± 0.16	188 ± 2	142 ± 2	7.2 ± 0.4
	Al-0.2Ce-0.1Y	40.4 ± 0.7	62.47 ± 0.16	147 ± 3	129 ± 1	3.4 ± 0.2
	Al-0.2Ce-0.12 Zr	42.5 ± 0.5	58.51 ± 0.11	157 ± 2	133 ± 1	5.1 ± 0.3
	Al-0.2Ce-0.2Sc-0.1Y	58.3 ± 0.6	61.77 ± 0.11	198 ± 2	162 ± 1	8.5 ± 0.2

Table 3 Hardness and electrical conductivity with error values of the alloys under as-cast and as-extruded states.

Alloys and states		Hardness (HV)	Electrical conductivity (% IACS)
As-cast	Al	23.3 ± 0.4	59.95 ± 0.52
	Al-0.2Ce	24.4 ± 0.7	54.79 ± 0.82
	Al-0.2Ce-0.2Sc	30.9 ± 0.7	54.3 ± 0.78
	Al-0.2Ce-0.1Y	24.5 ± 0.9	60.41 ± 0.83
	Al-0.2Ce-0.12 Zr	24.5 ± 0.7	56.55 ± 1.32
	Al-0.2Ce-0.2Sc-0.1Y	31.4 ± 0.7	54.13 ± 0.78
As-extruded	Al	25.3 ± 0.6	62.80 ± 0.09
	Al-0.2Ce	27.0 ± 0.4	63.04 ± 0.22
	Al-0.2Ce-0.2Sc	46.5 ± 0.5	61.55 ± 0.16
	Al-0.2Ce-0.1Y	30.9 ± 0.8	63.39 ± 0.12
	Al-0.2Ce-0.12 Zr	28.8 ± 0.5	59.45 ± 0.10
	Al-0.2Ce-0.2Sc-0.1Y	46.1 ± 0.3	62.05 ± 0.34

Fig. 2. The fracture morphologies of the studied alloys with different compositions after cold drawing: (a) macroscopic fracture morphology (Al-0.2Ce-0.1Y alloy); (b, c) microscopic fracture morphologies of Al-0.2Ce and Al-0.2Ce-0.2Sc alloy, respectively; (d, e) EDS results of the second phase particles of Al-0.2Ce-0.2Sc alloy.

Fig. 3. Polarization microscopy images of the as-cast alloys with different compositions: (a) commercial pure aluminum; (b) Al-0.2Ce alloy; (c) Al-0.2Ce-0.2Sc alloy; (d) Al-0.2Ce-0.1Y alloy; (e) Al-0.2Ce-0.12 Zr alloy; (f) Al-0.2Ce-0.2Sc-0.1Y alloy.

Fig. 4. TEM bright-field images for structural characteristics of the cold drawing alloys with different compositions: (a) Al-0.2Ce-0.12 Zr alloy; (b) Al-0.2Ce-0.2Sc alloy; (c) Al-0.2Ce-0.1Y alloy; (d) Al-0.2Ce-0.2Sc-0.1Y alloy.

Fig. 5. XRD patterns of the as-cast alloys with different compositions: (a) commercial pure aluminum; (b) Al-0.2Ce alloy; (c) Al-0.2Ce-0.2Sc alloy; (d) Al-0.2Ce-0.1Y alloy; (e) Al-0.2Ce-0.12 Zr alloy; (f) Al-0.2Ce-0.2Sc-0.1Y alloy.

Fig. 6. SEM images and EDS results of the as-cast alloys with different compositions: (a) Al-0.2Ce alloy; (b) Al-0.2Ce-0.1Y alloy; (c) Al-0.2Ce-0.2Sc alloy; (d) Al-0.2Ce-0.2Sc-0.1Y alloy; (e, f) amplifications of the positions of the red circles in (a); (g-i) amplifications of the positions of the red circles in (b)-(d), respectively; (j) EDS results of Al-0.2Ce alloy; (k) EDS results of Al-0.2Ce-0.1Y alloy; (l) EDS results of Al-0.2Ce-0.2Sc alloy; (m) EDS results of Al-0.2Ce-0.2Sc-0.1Y alloy.

Fig. 7. SEM images and EDS results of the hot extrusion alloys with different compositions: (a) Al-0.2Ce alloy; (b) Al-0.2Ce-0.2Sc alloy; (c, d) enlarged view of the red frames in (b) and (e), respectively; (e) Al-0.2Ce-0.1Y alloy; (f) Al-0.2Ce-0.2Sc-0.1Y alloy.

Fig. 8. EPMA elemental mapping of the Al-0.2Ce-0.2Sc-0.1Y alloy after hot extrusion: (a) Al; (b) Fe; (c) Y; (d) the scanning area; (e) Si; (f) Ce; (g) Sc.

Fig. 9. SEM images including the corresponding pictures removed the background for statistics of the cold drawing alloys with different compositions and a HAADF-STEM elemental mapping: (a) commercial pure aluminum; (b) Al-0.2Ce alloy; (c) Al-0.2Ce-0.2Sc alloy; (d) Al-0.2Ce-0.1Y alloy; (e) Al-0.2Ce-0.12 Zr alloy; (f) Al-0.2Ce-0.2Sc-0.1Y alloy. (g) HAADF-STEM element mapping of the Al-0.2Ce-0.2Sc-0.1Y alloy.

Table 4 The second phase particles (excluding nano-size precipitations) size and area percentage of the alloys after hot extrusion and cold drawing.

Alloys and states		Average particle size (μm)	Maximum particle size (μm)	Minimum particle size (μm)	Area percentage (%)
Hot extrusion	Al	2.25	12.32	1	0.58
	Al-0.2Ce	1.52	7.72	1	1.89
	Al-0.2Ce-0.2Sc	2.92	13.26	1	0.97
	Al-0.2Ce-0.1Y	3.19	13.72	1	1.92
	Al-0.2Ce-0.12Zr	2.96	11.80	1	1.32
	Al-0.2Ce-0.2Sc-0.1Y	3.98	26.23	1	2.03
Cold drawing	Al	2.47	11.06	1	0.54
	Al-0.2Ce	2.41	16.60	1	1.49
	Al-0.2Ce-0.2Sc	3.24	12.33	1	1.11
	Al-0.2Ce-0.1Y	3.30	13.56	1	1.96
	Al-0.2Ce-0.12Zr	3.10	12.98	1	1.40
	Al-0.2Ce-0.2Sc-0.1Y	3.79	21.11	1	2.38

Fig. 10. TEM bright-field images and HAADF-STEM elemental mapping for nano-size precipitations of the alloys with different compositions and states (the red circles in bright-field images represent nano-size precipitations and the blue circles represent defects such as dislocations and stacking faults): (a) Al-0.2Ce-0.12 Zr alloy after hot extrusion; (b) Al-0.2Ce-0.12 Zr alloy after cold drawing; (c) Al-0.2Ce-0.2Sc alloy after hot extrusion; (d) Al-0.2Ce-0.2Sc alloy after cold drawing; (e) Al-0.2Ce-0.2Sc-0.1Y alloy after hot extrusion; (f) Al-0.2Ce-0.2Sc-0.1Y alloy after cold drawing. (g) HAADF-STEM elements mapping of Al-0.2Ce-0.2Sc-0.1Y alloy after cold drawing.

Fig. 11. HRTEM images of typical size nano-size precipitations and defects along the [110]Al direction of the alloys under cold drawing state with different compositions: (a) Al-0.2Ce-0.12 Zr alloy; (b) Al-0.2Ce-0.2Sc alloy; (c) Al-0.2Ce-0.2Sc-0.1Y alloy; (d-g) fast Fourier transform (FFT) images of (a)-(c) and (h), respectively; (h) Al-0.2Ce-0.2Sc alloy; (i, j) inverse fast Fourier transform (IFFT) images of the Zones I and Zone II, respectively.

Fig. 12. Schematic diagram of the electrical conductive mechanism with different compositions and states.

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