Kinetics of diffusion induced recrystallization in the Cu(Al) system

Abstract

Diffusion induced recrystallization (DIR) occurs in Cu of Cu-clad Al (CA) wire during heating at temperatures around 200°C. The kinetics of DIR in the CA wire was experimentally observed in the temperature range of 210-270°C. In this temperature range, CA wires were isothermally annealed for various periods of 3 h to 960 h. Owing to annealing, layers of the α2, γ1, δ, η2 and θ phases form at the original Cu/Al interface, and the DIR region alloyed with Al is produced in the Cu phase from the Cu/α2 interface. The thickness l of the DIR region monotonically increases with increasing annealing time t. The DIR region grows faster at higher annealing temperatures. The new extended-model proposed in a previous study was used to analyze theoretically the experimental result. According to the analysis, l is proportional to t in the early stages but to a power function of t in the late stages. This means that the DIR growth is governed by the interface reaction at the moving boundary in the early stages but by the boundary diffusion across the DIR region in the late stages. Although the shortest annealing time of 3 h at 240-270°C is located in the early stages, most of the annealing times belong to the intermediate stages. Consequently, under the present experimental conditions, both the interface reaction and the boundary diffusion mainly contribute to the rate controlling process of DIR. On the other hand, the interface reaction is the rate controlling process for the shortest annealing time.