Influences Of Microstructure On Damping Capacity Of The Magnesium Alloys

As-cast AZ80 and Mg-Gd-Y magnesium alloys were hot extruded, and then a solid solution of 410℃×4h with a aging treatment of 170℃×45h were carried out to as-extruded AZ80, and a aging treatment of 225℃×40h were carried out to as-extruded Mg-Gd-Y. The microstructures of the magnesium alloys in different state were observed by means of Optical Micrograph, Scanner Electron Microscope, and Transmission Electron Microscope. The mechanical properties were tested by hardness test, and the damping capacities were measured by dynamic mechanical analyzer.The results showed that the as extruded alloys were composed of fine grains and a few second phases, revealing the occurrence of recrystallization during hot extrusion. Dislocations in a low density were observed. The grains of AZ80 alloy grew during solid solution treatment, and there still existed few second phase, Mg17Al12, after the treatment. The solute atoms precipitated along the grain boundary in the form of the second phase, Mg17Al12. The precipitation grew larger with a over-elongated aging time, leading to a reducing of hardness. Because of the high solubility of solute atoms and the two precipitated phases, i.e. Mg24Y5 and Mg5Gd, the Mg-Gd-Y alloy exhibited a obvious aging-hardening phenomena, and a sharp peak appeared within 3.5 h during the aging process.The investigation of the strain amplitude dependent damping capacity indicated that the curves showed strain amplitude dependent and independent regions. The curves were well interpreted by G-L dislocation model. The investigation of the temperature dependent damping revealed that the damping capacity increased with the rising temperature or the decreasing frequency. Two damping peaks were found at 50～100℃and 150～200℃respectively. The first peak was attributed to the movements of the dislocations on the basal plane, and the second peak was induced by the micro-slide of the interface between the matrix and the second phase.