Непружність та демпфуюча здатність магнію і сплавів Mg—Al в умовах циклічного високоамплітудного навантаження

Abstract

For Mg—Al alloys with magnesium content from 0 to 9%, measurements of anelastic deformation, damping capacity, and twinning start stresses were carried out. The method of cyclic loading under tension for a wide range of oscillations amplitudes with precision fixation of displacement was used. A method for determination of the start twinning deformation point σ0,002tw under conditions of cyclic loading is proposed, This stress characterizes the beginning of the inverse twinning stage, when the anelastic strain is 2∙10-5. Characteristics of σ0,002tw for technical magnesium and its alloys with aluminum in a wide range of plastic deformation are determined. An insignificant linear increase of σ0,002tw with increasing deformation was established for all Mg—Al alloys. The start twinning deformation point increases with increasing aluminum concentration. For low-alloy alloys with a solid-solution strengthening mechanism, the stress at the beginning of twinning increases insignificantly. For highly alloyed alloys, a significant increase of σ0,002tw stress is observed. It is established that repeated loading within the hysteresis loop to stresses. which is less than the maximum and is not accompanied by additional plastic deformation. If the level of applied stresses during repeated loading reaches the maximum value, the amount of plastic deformation after unloading increases. The addition in εpl gradually decreases with the rise of cycles number. The dependences of inelastic deformation and dissipated energy on the previous deformation degree for all investigated magnesium alloys demonstrate an extreme character. The growth of these characteristics is observed only in the initial part of the load to the residual deformation of 1—2%. With a further increase in deformation, the tendency to anelasticity and the damping capacity decrease. For the dependences dissipatson energy vs amplitude of loob stress, the maximum of dissipation energy is observed under the condition when the stress reaches a critical value, which corresponds to the beginning of prismatic or pyramidal sliding. Keywords: Mg—Al alloys, quasi-static cyclic loading, hysteresis loops, dissipation energy, damping capacity, elasticity, anelasticity, twinning start point.