Effect of annealing process on interface microstructure and mechanical property of the Cu/Al corrugated clad sheet

Abstract

In this research, annealing treatment was performed on the Cu/Al corrugated clad sheets fabricated by the corrugated cold roll bonding (CCRB) process. Interface microstructure evolution, interface phase development, intermetallic compound (IMC) growth kinetics, interface bonding strength, and electrical resistivity at various positions of the Cu/Al corrugated clad sheet were investigated under different annealing conditions. The IMC layers (CuAl2, Cu9Al4 and CuAl) with uneven thickness were formed at the Cu/Al corrugated interface during the annealing process. Interface defects caused by shear deformation can effectively reduce the growth activation energies of IMC sub-layer at positions I (back waist), III (front waist), and IV (trough). On the contrary, the interface brittle layers and overlayer can slightly increase the activation energy at position II (peak). The sequence of growth activation energies for IMC sub-layer was QCuAl<QCu9Al4<QCuAl2. When Cu/Al corrugated clad sheet was annealed at 350 °C for 30 min, the recrystallization degree of Al plate at position III (front waist) was higher than the position II (peak), which was mainly due to the severe plastic deformation at the front waist position. Meanwhile, the transformation from low angle grain boundaries (LAGBs) to high angle grain boundaries (HAGBs) of the Al plate was more likely to occur at position III (front waist). Interface shear strength presented wavy distribution along the interface when the Cu/Al corrugated clad sheet was annealed at 350 °C for different times. With the increase of annealing time, the average shear strength first increased and then decreased rapidly. When the annealing time was 60 min, the average shear strength reached the maximum value of 45.61 MPa, and the average electrical resistivity reduced to the minimum value of 11.56 × 10−8 Ω m. Considering the double influence of annealing process on bonding strength and electrical resistivity, it was recommended that the Cu/Al corrugated clad sheet be annealed at 350 °C for 60 min.