The effects of postrolling heat treatment on the mechanical property and microstructure of 1050 aluminum alloy and 304 stainless steel (SS) clad metals were investigated. Clad metals were made by cold rolling after surface treatments of both sheets followed by heat treatment at 500 °C for various annealing times. The effects of transformation of microstructure at the interface on bonding strength are discussed. The initial clad roll bonding of Al/stainless steel clad metal was bonded by mechanical locking at the interface. The protruding stainless steel in the interface is the diffusion route and forms the better joint with aluminum in the annealing process, which results in the enhancement of the bonding strength. Intermediate layers were formed for over 2 h. It resulted in the weakening of the bonding strength and the fracture surface transforms into a brittle structure. As Al/stainless steel clad metals were under 13% reduction ratio, it had the optimum bond strength with a heat treatment for 1 h at 500 °C.