The Effects Of A Small Amount Of Ce/Gd/Nd On Microstructural And Properties Of Mg Alloys

Mg alloys are becoming the ideal substitute materials in the high-technology fieldsand civil producing industries, attributing to its low density, high specific strength andspecific rigidity, excellent damping capacity and electromagnetic shielding capacity, aswell as recuperability. Meanwhile, the research and development of wrought Mg alloys areattracting more and more attentions.The influences of a small amount of rare earth elements (RE: Ce，Gd and Nd wt.%)and thermo-mechanical processing on recrystallization behaviour, microstructuralevolution and damping properties of Mg-Mn alloy system were discussed. Mg-RE alloyshave been prepared by zone purifying method followed by backward extrusion and hotrolling techniques. Microhardness tests were employed to determine the recrystallizationbehaviour. X-ray diffraction was used to evaluate the variation of the dislocation density.Electron back-scatter diffraction and transmission electron microscope were performed tomeasure texture and microstructural evolution. The mode of bending three points wascarried out to assess the damping properties. The recrystallization behavior was analyzedin terms of the Johnson-Mehl-Avrami-Kolmogorov model.The results revealed that the grain size of Mg alloys was reduced with the increasedconcentration of RE. The addition of a small amount of Ce accelerated the recovery. Therecovery temperature was decreased as the addition of Ce was increased. In addition, thegrain growth at elevated temperatures was impeded owing to the existence of finesecondary precipitates near to grain boundaries. Both strength and ductility were greatlyimproved by micro-alloying with Ce, which is mostly related to the fine grain size andhomogeneous secondary precipitate. By means of recrystallization volume fractionanalysis, the Avrami exponent of pure Mg sheet ranged from0.64to1.16and its rangewas reduced by adding RE. The acceleration of recovery in combination of the retardationof recrystallization were detected by the presence of RE. During the annealing process ofMg-1RE alloys, the decrease of dislocation density occurred in basal plane differencingfrom the reduction in <c+a> pyramid plane of pure Mg. A Snoek-K ster dislocationrelaxation at low temperatures was observed in Mg-1Ce alloy due to the variation of dislocation type. A damping peak of pure Mg at medium temperature was associated withthe self-diffusion of Mg. Comparatively; a stable damping peak at elevated temperaturewas detected in Mg-1RE alloys, which was ascribed to the Zener relaxation. All thesamples showed better damping properties in low frequency range than high frequencyrange. Meanwhile, the maximum damping value was improved and the temperature rangewas reduced with the addition of RE elements owing to the weakening texture. It providesa new choice for the development of low temperature and high plasticity magnesium rareearth alloy, which make the complex and thin wall magnesium alloy parts.