Changes in Mechanical Characteristics of Pre-Annealed Wires of Cu–Sn Alloy Manufactured by Continuous Draw Bending

Abstract

The changes in mechanical properties and microstructures of fine CuSn alloy wires manufactured by deep wire drawing and heat treatment, and of the wires deformed by draw bending were systematically investigated. During draw bending, the wires were subjected to the compressive/tensile or tensile/compressive strain in the longitudinal direction. As a result, it was confirmed that the softening caused by plastic deformation was induced when easing up the wire drawing strain by heat treatment were few, such as the decreasing strength and increasing elongation. Work hardening was induced when easing up the wire drawing strain by heat treatment were large, such as the increasing strength and decreasing elongation. With decreasing strength of softening induced by plastic deformation, increase in grain size is smaller than the strength deterioration. Additionally, it was confirmed that the occupancy probability of high-angle grain boundaries increases. This can be understood by considering that the many dislocations formed inside the grains are piled up in one direction during draw bending. Additionally, it is considered that ductility enhancement is caused by the increase in work hardening rate induced by the piled up dislocations.

Change in mechanical properties of fine copper wire manufactured by continuous rotary draw bending process

“…It was confirmed that draw bending in the final stage was able to produce fine wires with excellent mechanical properties. Additionally, Tokutomi et al (2012) confirmed that a wire specimen subjected to the CBD process had dislocation substructures inside the UFGs. However, the crosssectional shapes of wire specimens are irregular when the shaft in the bending area is fixed.…”

“…As shown in table, the alloy contains only a small amount of Sn as the alloying element. This alloy was the same as that used by Tokutomi et al (2012). Fig.…”

“…This value was empirically estimated by Tokutomi et al (2012) by removing a thin cross-sectional sample from a WD specimen using a focused ion beam (FIB) then observing the dislocations in a grain using a transmission electron microscope (TEM). The number of dislocations in each grain was derived from the relationship between the mean distance between dislocations and the spacing between neighboring agglomerations of dislocations.…”

Cross-Sectional Distributions of Mechanical Properties of Fine Cu–Sn Alloy Wire Manufactured by Continuous Rotary Draw Bending

“…12,13) Note that the tensile ductility of a wire-drawn specimen recovers after draw bending. Also, it was found that, during draw bending, the hardness of a wire-drawn specimen is lower than that of a specimen subjected to wire drawing, particularly on the inside of the bend.…”