Cu/Al bar clad material was fabricated by a drawing process and a subsequent heat treatment.During these processes,intermetallic compounds have been formed at the interface of Cu/Al and have affected its bonding property.Microstructures of Cu/Al interfaces were observed by OM,SEM and EDX Analyser in order to investigate the bonding properties of the material.According to the microstructure a series of diffusion layers were observed at the interface and the thicknesses of diffusion layers have increased with aging time as a result of the diffusion bonding.The interfaces were composed of 3-ply diffusion layers and their compositions were changed with aging time at 400 °C.These compositional compounds were revealed to be η2,(θ+η2),(α+θ) intermetallic phases.It is evident from V-notch impact tests that the growth of the brittle diffusion layers with the increasing aging time directly influenced delamination distance between the Cu sleeve and the Al core.It is suggested that the proper holding time at 400 °C for aging as post heat treatment of a drawn Cu/Al bar clad material would be within 1 h. Cu / Al bar clad material was fabricated by a drawing process and a subsequent heat treatment. During these processes, intermetallic compounds have been formed at the interface of Cu / Al and have affected its bonding property. Microstructures of Cu / Al interfaces were observed by OM, SEM and EDX Analyser in order to investigate the bonding properties of the material. Accredited to the microstructure a series of diffusion layers were observed at the interface and the thicknesses of diffusion layers have increased with aging time as a result of the diffusion bonding. The interfaces were composed of 3-ply diffusion layers and their compositions were changed with aging time at 400 ° C. These compositional compounds were revealed to be η2, (θ + η2), (α + θ) intermetallic phases. It is evident from V-notch impact tests that the growth of the brittle diffusion layers with the increasing aging time directly directly influenced delamination distance between the Cu sleeve and the Al core. It is suggested that the prope r holding time at 400 ° C for aging as post heat treatment of a drawn Cu / Al bar clad material would be within 1 h.