Using the method of molecular dynamics simulations, the dynamics of structure rearrangement in the course of relaxation in a three-dimensional aluminum is investigated via introduction of one-dimensional chains containing equal number of vacancies and interstitial atoms and located in close-packed positions along the <101 > directions. This model represents a starting material structure possessing regions with differing mass densities: m+ and m–. The process of relaxation is shown to proceed via a number of phases: generation of shock waves, nucleation of vortex displacements of atoms, transformation of shock waves into acoustic waves, and correlated high-velocity collective displacements of atoms from interstitial into vacancy positions. The latter displacements are developed at velocities much higher than acoustic velocity.