Mg-xLi (x=11, 14, 17wt.%)鎂鋰合金制振能之研究

Studies on Damping Capacities of Mg-xLi (x=11, 14, 17wt.%) Magnesium Alloys

李映萱(Ying-Hsuan Li)

指導教授 ： 吳錫侃

國立臺灣大學/工學院/材料科學與工程學研究所/碩士(2011年)

https://doi.org/10.6342/NTU.2011.10411

摘要

本研究針對極輕質LZ141及LZ171鎂鋰合金，進行固溶處理與室溫軋延等處理方法來改變其顯微組織，並利用動態機械分析儀(DMA)來測試其於各溫度下之制振能大小，以及藉由顯微組織觀察、XRD分析、硬度及拉伸試驗等，協助了解不同熱機處理條件對LZ141及LZ171合金的機械性質與制振能機制之影響。研究結果顯示，LZ141合金經固溶處理再室溫軋延70%，可明顯改善P1峰之制振能，使其在25℃即可達tanδ=0.025。另外，對不同熱機處理條件之LZ141合金分析其高溫制振背景(HTDB)活化能，發現其活化能與經DMA測試結束後之平均晶粒大小成正比，表示晶粒越小者具有越多可滑移之晶界，同時可提供越多的原子擴散通道，因此形成其HTDB所需之活化能也越低，但同時也會降低其潛變強度。對於含17wt.%鋰之LZ171合金，其比重降至1.32g/cm3，但也因鋰含量較高而使LZ171的制振能較LZ141合金差，且室溫軋延對P1峰制振能的提升效果有限，但隨著加工量的增加，P2峰會漸往低溫移動而有助於改善低溫之制振能。此外，雖LZ171合金之制振性質較差，但其機械強度卻不遜於LZ141合金，對於相同熱軋延條件之板材，LZ141合金之抗拉強度為127MPa，LZ171合金則為126MPa。本研究同時探討LAZ1110合金經固溶處理與室溫軋延等處理後之機械性質，並了解其室溫下時效之強化機制。研究結果顯示，LAZ1110合金經固溶處理後於室溫時效，約20hr可達到最高強度之peak ageing，此時抗拉強度可達245MPa，硬度最高為91.7Hv，之後其強度及硬度便隨著時效時間的增加而降低，約在500hr之後可達到平衡，硬度值固定在68Hv上下。若在固溶處理後立即施以室溫軋延，其強度可進一步提升至289MPa，並可有效減緩室溫時效的強度劣化趨勢並使其在較短的時間內達到平衡，約250hr即可達到平衡，硬度值平衡在75Hv。另外由XRD分析結果發現，室溫軋延會促進θ相之析出。

關鍵字

鎂鋰合金 ； 制振能 ； 高溫制振背景 ； 活化能 ； 室溫時效 ； 熱機處理

並列摘要

Cold-rolling and solid-solution treatments are conducted to strengthen extremely light LZ141 and LZ171 Mg-Li alloys. Damping capacities (DCs), microstructure observation, XRD tests, micro-Vickers hardness and tensile tests of strengthened LZ141/LZ171 alloys are investigated. Experimental results show that the DC (tanδ) can reach 0.025 at room temperature for solid-soluted and then 70% cold-rolled (SSCR) LZ141 alloy. For various thermo-mechanical treated LZ141 alloy, the activation energy of HTDB increases with increasing the grain size of the alloy after it has been heated in DMA load-cell up to 300℃. This indicates that the finer grain size can enhance the grain boundary sliding and accelerate the diffusion process simultaneously and therefore lessen the activation energy of HTDB. In the tanδ curve of LZ171 alloy, cold-rolled LZ171 alloy exhibits inconspicuous P1 peak, but P2 peak shift toward lower temperature with the higher degree of cold-rolling which can improve DC at lower temperature. Although LZ171 alloy has worser DC than LZ141 due to its higher Li content, there is not much difference of tensile strength in between these two alloys. The tensile strength of as hot-rolled LZ141 alloy and that 70% of CR LZ141 alloy is 127MPa and 170MPa, respectively, and that of LZ171 alloy is 126MPa for as hot-rolled and 180MPa for SSCR. The strengthening mechanism of LAZ1110 alloy is also investigated in this study. Solid-soluted LAZ1110 alloy reaches the maximum hardness (91.7Hv) after ageing at room temperature for 20hr. At this maximum hardness, 80% cold-rolled LAZ1110 alloy would enhance θ phase precipitation and cause the hardness decrease slightly, but retard the degradation of the hardness simultaneously when the specimen is aged at room temperature.

並列關鍵字

Mg-Li alloy ； damping capacity ； high temperature damping background ； activation energy ； room temperature ageing ； thermo-mechanical treatment

參考文獻

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