Al-Cu intermetallic phase growth in hybrid metal extrusion & bonding welds exposed to isothermal annealing or direct current cycling

Abstract

Joining of aluminium (Al) to copper (Cu) is of great interest to power generation, transportation and electronic industry. However, dissimilar metal joining often promotes intermetallic phase formation at the joined interface, which in redundancy can cause mechanical degradation and increased electrical resistance. The welding technique hybrid metal extrusion & bonding (HYB) is proven capable of joining dissimilar metals with a total intermetallic phase layer thickness < Image 1. To test how Al-Cu HYB joints perform as electrical conductors, a 6101 Al alloy HYB-welded to Cu is exposed to heat treatment at Image 2 or cycling of direct current density up to Image 3. In-depth micro- and nanostructure characterisation by (scanning) transmission electron microscopy and atom probe tomography are used to describe the structure and chemistry of the formed intermetallic phases.The Al-Cu HYB joints exhibited resilience against intermetallic phase growth during isothermal heat treatment or exposure to electric current. However, a non-symmetry is observed dependent on the current direction, creating voids in Cu near, and in the intermetallic layers when the current goes from Al to Cu. Detailed microstructure characterisation unveils Si and Mg in the intermetallic phase layers. Their origin and role in intermetallic phase growth are discussed.

Keywords

• Al-Cu intermetallic phase growth
• Al-Cu joints
• Atom probe tomography
• Hybrid metal extrusion &amp; bonding
• Intermetallic phase identification
• Precession electron diffraction