The paper aims to present a finite element model for the bonding process of metals at the microscale. To accomplish this, first, the mechanism of joining by plastic deformation at the microscopic level is explained. Then, based on the film theory of bonding, a finite element model is developed, which enables to simulate the bonding process between metallic layers subjected to large plastic deformation. The model presented in this paper takes into account the most important physical micro-mechanisms taking place during the bond formation process, i.e. (1) the breakage of the brittle oxide layer above the metallic surfaces, (2) the decohesion process occurring between the oxide layer and the metal substrate, (3) the extrusion of the substrate into the created cracks under large plastic deformations, and (4) the bond formation in between the fractured oxide layers. In addition, an extended version of a cohesive zone model is proposed to describe the bond formation between the metal surfaces. Finally, it is shown that the model can be used to provide a description regarding bond strength evolution. In this context, the effects of influencing factors, such as the degree of deformation and the thickness of the oxide layer, are numerically investigated. The presented finite element model can be regarded as a useful tool to characterize the key factors in joining processes such as roll bonding and cold forging.