Experiments have been carried out to investigate the damping behaviors of commercially pure
aluminum (L2) prepared by equal-channel angular pressing (ECAP). The damping characterization was
conducted on a DMTA-V apparatus. The internal friction was measured at frequencies of 0.1, 0.3, 1.0, 4.0 and
8.0 Hz over the temperature range of 20~150°C. The measured damping capacity shows that ultra-fine grained
structure pure Al (L2) prepared by ECAP has a damping capacity that is enhanced in comparison with coarse
one, especially when the temperature is higher than 60°C. The dependence of the damping capacity at room
temperature on the strain amplitude shows a nonlinear characteristic, and increases rapidly with the strain
amplitude (0) when 0 is comparatively low. While the strain amplitude is higher than certain value, the
damping capacity will become saturated slowly. The high damping capacity of the pure Al prepared by ECAP
was attributed to the high density of dislocations and ultra-fine grained structure.
Mg-1Si alloy doped with 1%Y was prepared by in-situ reaction synthesis. The effect of hot extrusion on the microstructure and elevated-temperature mechanical properties of the alloy was studied. The microstructures were analyzed by optical microscopy, scanning electron microscopy with energy dispersive X-ray spectroscopy and X-ray diffractometry. The results show that as-cast Mg-1Si-1Y alloy consists of dendritic α-Mg phase, eutectic needle-like Mg2Si phase and Mg24+xY5 phase precipitated from α-Mg, Mg2Si can be modified and refined by yttrium, and α-Mg grains can be refined by dynamic recrystallization occurred in hot extrusion process. The tensile strength and elongation of the alloy at ambient temperature are improved prominently by hot extrusion. The tensile strength and elongation of the extruded alloy is 185.3MPa and 24.3% at 120°C. The improved elevated-temperature properties of the alloy are ascribed to the fine-grained strengthening and dispersion strengthening from Mg2Si and Mg24+xY5 particles.
Damping capacities of the annealed nodular cast iron dense bar produced by horizontal continuous casting were measured by Dynamic Mechanical Analyzer. The relation of damping capacities with vibration amplitude, frequency and temperature was analyzed to investigate the damping mechanism of the alloy. The results show that the damping capacities increase with increasing temperature and frequency. The internal friction spectra exhibits two internal friction peaks at about 40°C and 150°C and caused by Snoek relaxation and Snoek-Köster relaxation, respectively. The maximum damping capacity can be obtained at about 63Hz. The damping is positive amplitude-dependent, whereas critical amplitude exists where the damping increases dramatically. The temperature-dependent damping results from the superposition effect of point-defect damping, grain boundary damping and interface damping, while dislocation damping is predominant in the frequency dependent damping. The amplitude dependent damping can be interpreted by G-L theory.
The ribbons of rapidly solidified Mg-6wt%Zn-1wt%Y-0.6wt%Ce-0.6wt%Zr alloy were reciprocatingly extruded and forward extruded into dense bar material. Room-temperature fatigue behavior of the alloy was tested in axial tension-tension stress condition. The fracture morphologies of the alloy after fatigue were observed by SEM. The results show that the fatigue limit is 159.2MPa with 106 cycles when the load frequency was 10Hz. The S-N curve of the alloy can be regarded as Type Ⅱ fatigue curve. The fatigue cracks originate from surface or subsurface of the fatigue specimens generally. The second phases or inclusions in these areas were prone to be the crack sources. The high fatigue properties of the alloy can be attributed to grain refinement strengthening and dispersion strengthening resulted from rapid solidification and reciprocating extrusion.
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