| Summary: | 碩士 === 國立臺灣大學 === 材料科學與工程學研究所 === 97 === Damping capacities (DCs) of AZ80 and LAZ1110 magnesium alloys are investigated by Dynamic Mechanical Analyzer (DMA) at the temperature range of 0-300℃. DC of the high-temperature damping background (HTDB) at 200-300℃ for AZ80 alloy increases significantly after 20% cold-rolling with or without aging. However, the activation energy of HTDB decreases from 1.69eV to 1.37eV, which indicates cold-rolling can accelerate alloy’s diffusion process and promote its creep development simultaneously. Consequently, the contrary cold-rolling effect on DC and creep resistance of AZ80 alloy should be taken into account carefully for its high-temperature applications. Three damping peaks P1, P2 and P3 are observed for LAZ1110 Mg-Li alloy. Severe cold-rolling can effectively improve the DC of LAZ1110 alloy at room temperature. The P3 peak located at about 200℃ shifts to lower temperature if the extent of cold-rolling increases. Experimental results show that, after severe cold-rolling, the formation of P3 peak is well-related to β(200) preferred orientation and caused by recrystallization process. Besides, high damping criterion (tanδ≧0.03) can be met at room temperature for 80% cold-rolled LAZ1110 sheet tested at 0.1Hz low frequency or at 30-35μm operating amplitude.
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