We study the magnesium-thermal beryllium condensate in the course of natural aging after several procedures of treatment by weak constant magnetic fields. The amplitude-time dependences of the effective shear modulus (Gef ~ f2), low-frequency internal friction, the parameter r, and the ratio of dislocation velocities Vafef /V0 are analyzed. It was revealed that the hysteresis in the f2(γ) curves disappears after ~120 h of natural aging and the sign of r(γ) and Vafef /V0(γ) is inverted. The nature of the detected effects is connected with the appearance of microcracks in the stage of elastic deformation and their healing as a result of the viscous motion of unpinned dislocations in the field of point defects in the basal slip plane.