Investigation of joint interface and cracking mechanism of thick cladding of copper on aluminum by equal channel angular pressing (ECAP)

Abstract

Joint interface and cracking mechanism during thick cladding of copper on aluminum have been investigated. For this purpose, deformation of Al-Cu bimetallic inserts during equal channel angular pressing (ECAP) is investigated using finite element method (FEM). FEM results show that both metals undergo similar straining during ECAP. However, the values of maximum principal stresses that may cause cracking are significantly higher in the casing tube which continues to more significant increase by increasing number of ECAP passes. Therefore, it is concluded that cracking is likely to occur in the copper casing if ECAP deformation of the composite exceeds two passes. This is in agreement with the experimental results in which cracking is observed in the fourth pass of ECAP. Cracking in the copper casing at 45 degrees with respect to the joint interface is attributed to the existence of tensile maximum principal stresses caused by severe shear stresses at the interface. Shear bond strength between the aluminum core and the copper casing in the deformed composite increases up to 3 passes and reduces in the fourth pass. The increase is preliminary attributed to increasing the joint fraction between aluminum and copper substrates and the reduction in the fourth pass is correlated to formation of cracks on the copper substrate. Estimation of shear friction factor (m) between aluminum and copper at the joint interface indicates that it is around 0.21 independent from the number of ECAP passes. Indeed, the number of ECAP passes can change the joint surface fraction, however, it is not effective on the nature of the joint. Indeed, m smaller than 1 indicates that a solid metallurgical bonding has not formed over the joint and mechanical bonding is mostly responsible for the joint strength. In addition, as m is not a function of number of passes, it is concluded that the type of bonding at the interface is not affected by number of ECAP passes.