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Student Number 973203049
Author young you(楊祐炘)
Author's Email Address No Public.
Statistics This thesis had been viewed 738 times. Download 551 times.
Department Mechanical Engineering
Year 2009
Semester 2
Degree Master
Type of Document Master's Thesis
Language zh-TW.Big5 Chinese
Title Mechanical Properties of Super Light Magnesium-Lithium Alloy
Date of Defense 2010-06-29
Page Count 120
Keyword
  • Grain refining
  • Magnesium-Lithium alloy
  • Rolling
  • Abstract This research discusses the microstructures and mechanical properties of a series of super light magnesium-lithium alloys. The density of the Mg-Li alloy is approximately 1.46g/cm3. Previous researches indicate that Mg-Li alloys lack of strength, therefore we wish to increase its strength by adding Sc and Be into the alloy, creating four alloys,LAZ1110, LAZ1110+Be, LAZ1110+Sc, LAZ1110+ Be &Sc,respectively.
    And we also use different processes to enhance the mechanical properties, such as solid solution treatment and cold work strengthening. On the other hand, we use thermo mechanical treatment to obtain a refined grain size and attain superplasticity. Experimental results indicate that when the Mg-Li alloy is extruded and rolled, the as-extruded material with 90% rolling reduction can obtain a maximum tensile strength about 200Mpa. Another process is extrusion plus solid solution and then cold rolling. Due to the superimposition effect of solid solution strengthening and cold work strengthening, the material after 90% rolling reduction can obtain a maximum strength of 246Mpa. The last process, the material is extruded, solid solution treated and cold rolled before aged. The material aged under room temperature after 20~40hrs will have peakaging with tensile strength of 253Mpa.
    In microstructures, experimental results show that all four alloys possess a single β-phase after solid solution treatment. After rolling the grains are elongated and α-phase will precipitate with increasing rolling percentage. The four alloys’ specimens after extrusion, solid solution and cold rolling were annealed at 50、100、150、200、250℃, respectively, for 30min. Their grain size increases with increasing annealing temperature. When annealing temperature reaches 250℃, uniformed static recrystalled grains can be observed, especially in specimens with 30% and 60% rolling reduction whose grain size is less than 10μm which is suitable for superplasticity tests. When Mg-Li alloys are placed under room temperature α-phase will precipitate resulting in a decrease in strength and overaging.
    Table of Content 摘要
    Abstract………………………………………………………………………I
    誌謝……………………………………………………………………………III
    目 錄V
    圖目錄IX
    表目錄XVI
    第一章 緒論1
    1-1 前言1
    1-2研究動機與目的2
    第二章 文獻回顧7
    2.1鎂合金的材料特性8
    2-2合金元素添加對鎂合金性質之影響10
    2-2-1 添加鋰(Li)對鎂合金的影響10
    2-2-2添加鋅 (Zn) 對鎂合金的影響11
    2-2-3 添加鋁 (Al) 對鎂合金的影響11
    2-2-4添加鈧 (Sc) 對鎂合金的影響12
    2-2-5添加鈹 (Be) 對鎂合金的影響12
    2-3 鎂合金規格符號13
    2-4 鎂合金的分類13
    2-5金屬材料再結晶理論15
    2-5-1 冷作加工儲存能16
    2-5-2 儲存能的釋出及再結晶驅動力16
    2-5-3再結晶晶核的形成17
    2-5-4再結晶溫度18
    2-6鎂合金晶粒細化之方法與理論18
    2-6-1鎂合金晶粒細化之影響18
    2-6-2晶粒細化的方法19
    2-7鎂合金的超塑性19
    2-8超輕鎂鋰合金經鑄造、擠製及ECAE等製程達超塑性之相關研究文獻20
    第三章 實驗方法與設備32
    3-1實驗材料32
    3-2 實驗設備33
    3-3 成份分析34
    3-4實驗步驟34
    3-5 滾軋+熱機處理34
    3-6 微結構組織35
    3-6-1 金相觀察(OM)及晶粒大小量測35
    3-6-2 掃瞄式電子顯微鏡(SEM)36
    3-7 XRD測試36
    3-8 機械性質測試36
    3-8-1 硬度試驗36
    3-8-2 常溫拉伸測試37
    3-8-3高溫拉伸實驗37
    第四章 結果與討論47
    4-1顯微組織觀察47
    4-1-1擠製材之金相47
    4-1-2 擠製、固溶後之金相48
    4-1-3 固溶處理後冷軋之金相組織49
    4-1-4 退火處理後之金相組織50
    4-1-5高溫拉伸後之金相組織51
    4-2 XRD結構分析52
    4-2-1 固溶處理與自然時效後之XRD結構分析52
    4-2-2 固溶處理後冷軋延自然時效之XRD結構分析53
    4-3 硬度測試54
    4-3-1 擠製後經不同固溶溫度與時間下再置於室溫下之時效硬度54
    4-4 常溫拉伸試驗54
    4-4-1 擠製及軋延之機械性質54
    4-4-2 擠製、然後固溶在軋延之機械性質55
    4-4-3固溶後軋延自然時效之機械性質56
    4-4-4固溶軋延後退火之抗拉強度57
    4-5高溫拉伸試驗57
    4-6 SEM破斷面觀察58
    第五章 結論113
    參考文獻115
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    Advisor
  • shyong Lee(李雄)
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    Date of Submission 2010-07-02

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