Influence of Isothermal Annealing on Mechanical Properties of Cu-Clad Al Wire

抄録

The influence of isothermal annealing on mechanical properties of the Cu-clad Al (CA) wire was experimentally examined to better understand the annealing mechanisms that occur in the CA wire. In the experiment, the CA wire was prepared by drawing to decrease the diameter d from 10 mm to 2.9, 1.5 and 0.5 mm. The CA wires with these three different diameters were isothermally annealed at temperatures of 423–603 K (150–330°C) for various periods between 10.8 ks and 3456 ks (3 and 960 h). At room temperature, tensile tests were performed on the CA wire using an Instron type testing machine, and hardness tests were made on the Cu layer and the Al core of the CA wire utilizing a micro Vickers hardness testing machine. For the CA wire without annealing, the ultimate tensile strength s_u is 231, 215 and 198 MPa for d = 0.5, 1.5 and 2.9 mm, respectively, and the elongation e_u is 0.4, 0.4 and 1.2% for d = 0.5, 1.5 and 2.9 mm, respectively. Due to isothermal annealing, recovery and recrystallization take place in both the Cu layer and the Al core of the CA wire, and an intermetallic layer consisting of various Cu–Al compounds forms at the Cu/Al interface. The intermetallic layer promotes formation of cavity at the Cu/Al interface during the tensile test. As the thickness l of the intermetallic layer reaches to the critical thickness l_m, s_u attains to the minimum value, and e_u takes the maximum value. Here, l_m = 1–2 µm for d = 0.5–2.9 mm, respectively. For l > l_m, however, s_u is insensitive to l, but e_u decreases with increasing thickness l. Thus, the appropriate combination of the annealing temperature and time is essentially important to realize the optimal mechanical properties of the CA wire.

Fig. 9 The results in Fig. 8(b), 8(d) and 8(f) are represented as open circles, triangles and rhombuses, respectively. The corresponding results reported by Hug and Bellido⁷⁾ are also shown as solid squares.