Dowel-like morphology of Cu2Al3 enhances shear strength of interfacial layers in Cu-Al composites

Abstract

Developing bimetallic interfaces with high interfacial bonding strength is important for metallic composites used under harsh service conditions. However, the formation of brittle intermetallic compounds is unavoidable for some interface combinations, resulting in a significant deterioration of bonding strength. In this work, we demonstrate the development of a Cu alloy/Al alloy interface with a shear strength of 126±15 MPa – a value almost twice that reported in previous studies. The exceptional interfacial bonding strength is attributed to a special interface structure, composed of brittle intermetallic compound layers connected internally by dowels of a metastable Cu2Al3 phase, achieved via alloy design and process control. During solid-liquid composite processing, a liquid diffusion layer forms at the interface between the Cu and Al alloys. A precursor Cu4Al7Ni phase then develops at the Cu side and transforms into a metastable Cu2Al3 phase with a banded structure. Finally, layers of Cu9Al4 and CuAl2 layers form, which are fully connected to the Cu2Al3 phase. The banded arrangement of the Cu2Al3 phase acts to block crack propagation and deflect cracks into the eutectic layer and Al alloy, resulting in an ultra-high interfacial bonding strength. This work demonstrates that high interfacial bonding strength can be achieved by tailoring the interface structure instead of by decreasing the interface thickness, and thus paves a new way for developing high-performance bimetallic interfaces.