Strain-Induced Balancing of Strength and Electrical Conductivity in Cu-20 wt% Fe Alloy Wires: Effect of Drawing Strain

doi:10.1007/s40195-025-01857-7

Abstract

Abstract:

The effects of drawing strain during intermediate annealing on the microstructure and properties of Cu-20 wt% Fe alloy wires while maintaining constant total deformation were investigated. Intermediate annealing effectively removes work hardening in both the Cu matrix and Fe fibers, restoring their plastic deformation capacity and preserving fiber continuity during subsequent redrawing. The process also refines the Fe phase, leading to a more uniform size distribution and straighter, better-aligned Cu/Fe phase interfaces, thereby enhancing the comprehensive properties of the alloy. The magnitude of drawing strain during intermediate annealing plays a critical role in balancing the mechanical strength and electrical conductivity of redrawn wires. A lower initial drawing strain requires greater redrawing strain, leading to excessive hardening of the Fe fibers, which negatively impacts the electrical conductivity and tensile plasticity. Conversely, a higher initial drawing strain can result in insufficient work hardening during the redrawing deformation process, yielding minimal strength improvements. Among the tested alloys, H/3.5 wires show a slight reduction in strength and hardness compared to W and H/4.5 wires but exhibit a significant increase in tensile elongation and electrical conductivity. The tensile strength was 755 MPa, and the electrical conductivity was 47% international-annealed copper standard (IACS). The optimal performance is attributed to the formation of a high-density, ultrafine Fe fiber structure-aligned parallel to the drawing direction, which is achieved through a suitable combination of the drawing process and intermediate annealing.

Key words: Cu-Fe alloy, Drawing deformation, Intermediate annealing, Strength, Electrical conductivity

Fei Yang, Canhui Wu, Ruifeng Li, Wenyi Huo, Liming Dong, Feng Fang. Strain-Induced Balancing of Strength and Electrical Conductivity in Cu-20 wt% Fe Alloy Wires: Effect of Drawing Strain[J]. Acta Metallurgica Sinica (English Letters), 2025, 38(7): 1246-1260.

Figures/Tables 19

Fig. 1 Schematic diagram of the drawing deformation process

Fig. 2 Axial a-d and transverse e-h structures of the Cu-Fe wires: a, e W; b, f H/4.5; c, g H/3.5; d, h H/3

Fig. 3 Thickness of the Fe fibers: a W; b H/4.5; c H/3.5; d H/3

Fig. 4 Orientation distribution and corresponding IPF of the Cu-Fe wires: a, e W; b, f H/4.5; c, g H/3.5; d, h H/3

Table 1 Volume fraction (%) of the texture component

Texture	W	H/4.5	H/3.5	H/3
< 111 >	37.2	22.3	20.3	32.3
< 100 >	22.4	4.7	5.8	21
< 112 >	13.8	31.4	34.6	15.2
Rest	26.6	41.6	39.3	31.5

Fig. 5 3 mm wires annealed at 500 °C: a recrystallized Cu grains and b dislocation line

Fig. 6 Grain boundary and misorientation distributions: a W; b H/4.5; c H/3.5; d H/3

Table 2 Grain size statistics of the Cu phase (μm)

	W	H/4.5	H/3.5	H/3
GZ_p	0.73	0.77	0.96	1.06
GZ_v	0.27	0.28	0.34	0.36
Ratio	2.70	2.75	2.82	2.94

Fig. 7 TEM microstructure of the W wire and corresponding element distributions: a Cu matrix and b Fe phase

Fig. 8 TEM microstructures of H/4.5 wires: a1 Cu matrix; a2, a3 Cu and Fe distributions; b1, b2, b3 twins and corresponding FFTs; c1 Fe matrix; c2, c3 Cu and Fe distributions

Fig. 9 TEM microstructures of the H/3.5 wire and elemental distribution: a Cu matrix and b Fe phase

Fig. 10 Mechanical properties: a tensile stress-strain curves and b hardness

Fig. 11 Fracture morphology and local enlargement images: a1, a2 W; b1, b2 H/4.5; c1, c2 H/3.5; d1, d2 H/3

Fig. 12 Electrical conductivity of intermediate annealed wires

Fig. 13 a-f Schematic diagram of the evolution of the Fe phase structure during drawing deformation

Fig. 14 Orientation distribution and phase diagram distribution: a, b drawing a 4.5 mm wire; c, d drawing a 3.5 mm wire; e, f annealing a 4.5 mm wire; g, h annealing a 3.5 mm wire; in b, d, f, h, the green is the Fe phase, and the red is the Cu phase

Table 3 Comprehensive properties of the redrawn wires

	Tensile stress (MPa)	Elongation (%)	Hardness (HV)	% IACS
W	763	0.5	177.5	39.7
H/4.5	776	1	167	42.2
H/3.5	755	5.1	164.5	47.2
H/3	735	4.6	158	48

Table 4 Statistical analysis of the strengthening contribution (MPa) of the Cu-Fe alloys

		W	H/4.5	H/3.5	H/3
Fe	d (μm)	0.35	0.43	0.43	0.43
	${\sigma }_{\text{GB}}$	202.8	182.9	182.9	182.9
	ρ (10¹⁵ m⁻²)	2.89	2.23	2.17	2.14
	${\sigma }_{\text{DIS}}$	522.3	459.1	453.2	450.3
	${\sigma }_{\text{yFe}}$	785.1	702	696.1	693.2
Cu	d (μm)	0.27	0.28	0.34	0.36
	${\sigma }_{\text{GB}}$	230.9	226.8	205.8	200
	ρ (10¹⁵ m⁻²)	1.84	1.75	1.67	1.58
	${\sigma }_{\text{DIS}}$	367.7	358.6	350.3	340.8
	$\Delta {\sigma }_{\text{s}}$	35	35	35	35
	${d}_{\text{p}}$ (nm)	37.5	35.2	36.4	34.8
	${f}_{\text{p}}$ (%)	1.03	2.65	2.83	2.81
	$\Delta {\sigma }_{\text{p}}$	73.8	128.4	129.5	133.7
	${\sigma }_{\text{yCu}}$	732.4	773.8	745.6	734.5
Cu-Fe	The ${\sigma }_{\text{y}}$	743.9	758.0	734.7	725.4
	Mea ${\sigma }_{\text{y}}$	-	-	732.4	717.8

Fig. 15 Performance comparison between strength and electrical conductivity [16,22,41,44,45,46]

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