Mechanochemical joining in cold roll-cladding of tri-layered Cu/Al/Cu composite and the interface cracking behavior

• The nature of interface bonding in Cu/Al/Cu clad was examined by fracture analyses.
• Mechanochemical bonding plays an important role in joining Cu/Al at room temperature
• Interface strength is dependent on the area fraction of various bonding natures.
• Cu/Al interface was strong enough to induce the crack through the softer Al matrix.
• The design and control of the area fraction of specific bonding is important.

The nature of interface bonding in tri-layered Cu/Al/Cu clad-composite processed by cold roll-bonding was examined by fracture surface analyses. The peeled-off fracture surface of Cu side revealed polygon-shaped intermetallic region, Al islands with the central ridge-like pattern and valley-trail like Cu network. The area fraction of region with intermetallics, region with mechanical metallic bonding and unbonded/weakly bonded region was observed to be 0.148, 0.596 and 0.256 respectively. The mechanochemical bonding through pressure- and heat-induced intemetallic formation was found to be important in joining Cu and Al even in cold-roll-bonding in addition to typical mechanical joining. Cu/Al metallic joint interface was strong enough to induce the crack to propagate through the softer Al matrix adjacent to the mechanically joined interface and along the intermetallic layer.