Generally, the elimination of the voids in bond interface is considered to be the rate-controlling mechanism for diffusion bonding. In an earlier paper, the author proposed a new theoretical model for solid-state diffusion bonding of similar matals, in which the grain growth across the bond interface was considered to be the governing mechanism for diffusion bonding. The aim of the model is to understand how the joint strength is affected both by process variables (temperature, pressure, time) and by the microstructures of the materials being joined. In this paper, the mechanism of grain growth and recrystallization is discussed, and the calculation of an appropriate kinetic equation is made based on a diffusion bonding experiment on a hot-rolled 7075 aluminum alloy. The calculated results basically agree with those of the experiment.