Mechanical Strength and Electrical Conductivity of Cu–In Solid Solution Alloy Wires

Abstract

Conductive spring wires for application in electrical components require high strength, high electrical conductivity, and convenient manufacturability. Copper–indium (Cu–In) solid solution alloys are suitable candidates for such wires because they exhibit effective solid solution strengthening without significantly decreasing the conductivity. Herein, we systematically investigate the microstructure of Cu–In alloy wires fabricated by severe drawing, along with their mechanical and electrical properties. During the initial drawing stages, high-density deformation twins are generated in the Cu–In alloy because the In solute efficiently reduces the stacking fault energy (SFE) of the Cu matrix. These deformation twins promote grain refinement during subsequent drawing. The Cu–5.0 at. pct In alloy wire, drawn severely to an equivalent strain of 4.61, possesses ultrafine grains measuring 60 to 80 nm with a high density of dislocations, resulting in excellent yield strength, tensile strength, and conductivity of 1280 MPa, 1340 MPa, and 24 pct relative to the International Annealing Cu Standard, respectively. These properties were comparable to those of age-hardenable Cu–Be and Cu–Ti alloys; thus, our results demonstrate that tuning the In content of the Cu matrix to reduce the SFE and optimizing the deformation strain to refine the grain size significantly improves the performance of alloy wires.

Appendix: Hall–Petch Relationship for Cu–5.0 At. Pct In Alloy

We surveyed the relationship between the grain size and yield strength of the Cu–5.0 at. pct In alloy with a single Cu solid solution (Cu_ss) phase. The Cu–5.0 at. pct In alloys were groove-rolled to a rod shape (with a 3.0 mm diameter) and heat-treated within a Cu_ss single-phase region at 500 °C for 1 and 10 minutes, at 600 °C for 10 minutes, and at 700 °C for 10 minutes to obtain Cu_ss single phase alloys with equiaxed grain microstructures with equivalent diameters of 7, 8, 20, and 100 μm. Figure A-1 shows the relationship between the grain size and yield strength of the Cu–5.0 at. pct In alloy, together with that of pure Cu.^[43] From the yield strength plots of the Cu–5.0 at. pct In alloy, Δσ^y_gb can be approximated using Eq. [A-1]:

$$ \Delta \sigma^{{\text{y}}}_{{{\text{gb}}}} = 123 + 190/d_{{\text{g}}}^{1/2} , $$

(A-1)

where Δσ^y_gb denotes the increase in the yield strength caused by the GBs, and d_g represents the grain size.

Fig. A-1

Relationship between grain size and yield strength in Cu–5.0 at. pct In alloy, together with that in pure Cu