Effect of Crystal Orientation on Amplitude-Dependent Damping in Magnesium

Abstract

The amplitude-dependent internal friction and Young's modulus have been measured as a function of the crystal orientation in magnesium single crystal specimens of 99.9% purity by using a flexural vibration method at room temperature. It has been found that, if only the basal slip system is operative, Schmid's law holds for the orientation dependence of the breakaway stress gests that the amplitude-dependent internal friction is caused by the movement of basal dislocations. In addition the analysis of the internal friction data based on the Granato-Lticke theory has also given evidence that the amplitude-dependence of internal friction is caused by the static hysteresis due to the interaction of basal dislocations with impurity atoms. Complementary experiments using polycrystalline specimens of magnesium and zinc showed that the amplitude-dependence of internal friction was extremely sensitive to the crystallographic orientation of individual grains.large amplitude-dependence of internal friction. In contrast a specimen with columnar grains whose longitudinal direction was almost parallel to the specimen axis had a much larger value of a8 and displayed very little amplitude-dependence of internal friction. Similar behaviour was observed in two zinc specimens having quasi-equiaxed grains and the (0001) rolling texture, respectively. It was concluded that the Schmid factors in individual grains played the most important role in the amplitude-dependent internal friction of hexagonal close-packed metals.

Elastic and Damping Properties of AZ31 Magnesium Alloy Sheet Processed by High-Temperature Rolling

“…The range of strain amplitude was set to from 0:5 Â 10 À5 to 1:1 Â 10 À3 . The internal friction of both the specimens exhibited strain-amplitude dependent with the same manner as the previous studies, 13,15,16) suggesting that the main damping mechanism is the dislocation damping, which is caused by the interaction between the dislocation and impurity atoms. In Fig.…”

“…[13][14][15][16][17][18][19] However, damping property of commercial magnesium alloys such as Mg-Al-Zn alloys is not so high compared with that of pure magnesium, 15,17) thus, application of magnesium alloy sheets for damping materials is still limited. 20) In general, elastic and damping properties of metals are recognized to be dependent on microstructural factors such as grain size, precipitates, texture and so on.…”

“…20) In general, elastic and damping properties of metals are recognized to be dependent on microstructural factors such as grain size, precipitates, texture and so on. Among the limited literatures, Sugimoto et al 13) investigated the effects of crystal orientation on the elastic and damping properties of pure magnesium, and suggested that elastic and damping properties strongly depend on the crystal orientation according to the Schmid's law. These reports imply that magnesium alloy sheets with significant weak basal texture may exhibit different elastic and damping properties with those of the conventional magnesium alloy sheets with strong basal texture.…”

A Study of Damping Capacity in Magnesium Alloys

“…There are, generally, three different methods for strengthening materials; (1) solution hardening, (2) precipitation hardening, and (3) hardening by use of natural composite materials. Of the three methods, (1) and (2) seem to be not suitable for the present purpose, because the mobility of dislocations in magnesium would be decreased to a large extent by the solute atoms or the precipitated particles and hence the damping capacity would be very much reduced. Therefore, (3) seems to be the only way to improve the mechanical strength of the magnesium alloy without reducing the damping capacity.…”

“…According to the previous work on the internal friction and Young's modulus in single crystal and polycrystalline samples of pure magnesium of 99.95% purity, a well-defined amplitude-dependence of the internal friction and Young's modulus was found to exist in some special cases (1). The amplitude-dependent internal friction was very sensitive to the crystal orientation.…”