Effect of the dynamic evolution of dislocations under cyclic shear stress on damping capacity of AZ61 magnesium alloy

Abstract

The effect of the dynamic evolution of dislocations on damping capacity of AZ61 magnesium alloy was investigated by using dynamic mechanical analysis and transmission electron microscope. The results indicate that the dynamic evolution of dislocations caused by the increased cyclic shear stress significantly influences the damping capacity, and it exhibits four regions. In the first region, the low damping capacity is caused by forced vibrations of dislocation segments pinned by weak pinning points. The second region is the linear increase of damping capacity, the dislocations breakaway from weak pinning points is responsible for it. The third region is characterized by a non-linear increase of damping capacity, and the growth rate of the damping capacity increases as the increase of shear stress amplitude, dislocation multiplication and dislocation movement in the cyclic shear stress acting plane lead to the non-linear increase of mobile dislocation density, which is responsible for that. Because dislocation pile-up causes the mobility of the dislocation lines decreases, the growth rate of the damping capacity decreases - the fourth region.