Effect of Microstructure on Strength and Electrical Conductivity of Cu–3.8 wt%Zr Alloy Wires

抄録

Wires of a Cu–3.8 wt% Zr alloy were produced by conform extrusion followed by wire drawing up to 0.2 mm in diameter (S wire), or by conform extrusion and subsequent annealing during wire drawing up to 0.2 mm (IA wire). The effects of microstructure on the strength and electrical conductivity of the S and IA wires were investigated. The severely drawn S and IA wires had a mixed microstructure consisting of a Cu parent phase with fine grains, fibrous eutectics elongated along the drawing direction, and granular eutectics. The 0.2% proof stress (σ_0.2) and tensile strength (σ_u) of the S and IA wires increased monotonically with increasing drawing ratio (η). The S wire with η = 7.8 exhibited large values of σ_0.2 = 1080 MPa and σ_u = 1320 MPa. The S and IA wires having the mixed microstructure are strengthened primarily by high density of dislocations and grain refinement in the Cu phase and by the presence of fibrous and granular eutectics. The electrical conductivity (E) of the S wire increased in the early stage of wire drawing and then began to decrease, dropping to 42% IACS at η = 7.8. The increase in E is caused by refining of the eutectics, which was formed during casting, toward the granular or fibrous form. The E value of the IA wire after annealing was high, 72%IACS, and then decreased as η increased. Values of E of the S and IA wires with the mixed microstructure was estimated by applying rules of mixtures. The estimated values of E are in agreement with the measured values of E. It is shown that the presence of the fibrous and granular eutectics significantly increases the electrical conductivity.

 

This Paper was Originally Published in Japanese in J. Japan Inst. Copper 60 (2021) 16–23.

Fig. 2 SEM images of the vertical cross-sections of (a) the as-cast, (b) conform-extruded, (c) 5S, (d) 0.6S, and (e) 0.6IA specimens.