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研究生:蔡原宗
研究生(外文):Yuan-tsung Tsai
論文名稱:摩擦攪拌AZ61鎂合金於200℃~250℃拉伸性質及動態再結晶之應變速率效應研究
論文名稱(外文):Effect of Strain Rate on the Tensile Properties and DRX of Friction Stir Processed AZ61 Mg Alloy at Elevated Temperature from 200℃ to 250℃
指導教授:呂傳盛呂傳盛引用關係陳立輝陳立輝引用關係
指導教授(外文):Truan-Sheng LuiLi-Hui Chen
學位類別:碩士
校院名稱:國立成功大學
系所名稱:材料科學及工程學系碩博士班
學門:工程學門
學類:材料工程學類
論文種類:學術論文
論文出版年:2008
畢業學年度:96
語文別:中文
論文頁數:69
中文關鍵詞:摩擦攪拌製程晶界滑移AZ61鎂合金動態再結晶
外文關鍵詞:AZ61FSPDRXGBS
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  鎂合金具有低密度、高比強度、回收性佳等優點,因而普遍使用在交通工業、3C產業上。鎂合金於室溫下成形性不佳的原因歸因於其HCP結構於室溫下滑移系統不足,需要在高溫環境中加工成形,導致成本提高,故本實驗使用摩擦攪拌製程(Friction Stir Process, FSP)進行改質,可以獲得再結晶之細小晶粒,以得到較好加工性。首先將AZ61鎂合金材料進行退火處理後施以FSP,進行顯微組織觀察,以及在不同溫度(200℃至250℃)和應變速率(8.33×10-3sec-1、1.67×10-3sec-1 及 8.33×10-4sec-1)下進行拉伸試驗以了解織構及洋蔥環效應對機械性質之影響。
  在顯微組織方面,AZ61-O鎂合金在經過FSP後SZ區有明顯晶粒細化效果;由XRD結果顯示,銲道上織構為HCP的基面沿著攪拌棒的凸梢圓周排列。拉伸試驗結果顯示,O材及FSP材在200℃以上的應力-應變曲線可以觀察到有抖動現象產生,根據觀察結果可知這是由於材料在拉伸過程中產生動態再結晶所致。各試料的降伏強度、抗拉強度及均勻延伸率皆隨拉伸溫度上升及應變速率下降而下降,總延伸率隨拉伸溫度上升及應變速率下降而有增大傾向。值得注意的是FSP材於200℃拉伸之總延伸率雖小於O材,但是升溫至225℃及250℃後之總延伸率卻大於O材,根據實驗結果可確認是由於FSP後之織構特徵導致拉伸時較易產生形變雙晶。
  FSP後材料抗拉強度及降伏強度下降,延性提升之原因,推測因大量產生動態再結晶使材料軟化,因此促進擴散頸縮行為發生,並降低材料的均勻延伸率;根據n值量測,材料於高溫低應變速率下產生晶界滑移,並導致應變硬化效果,降低動態再結晶對於材料的軟化作用,進而提升延性。
 Magnesium alloys have several advantages including low density, high specific strength and well recyclability. There are common applications in traffic and 3C industry. The inherently poor workability exists in Magnesium alloys at room temperature due to the limited slip systems associated with the HCP crystal structure. Since high temperature forming is applied in general, it would cause more cost. Therefore, mechanical properties are improved by Friction Stir Process (FSP), and the grains would be well recrystallized to increase the workability.
 Full-annealed magnesium alloys of AZ61, called AZ61-O, are processed by FSP. In order to study the effects of microstructure, texture, and onion rings by FSP. AZ61-O and FSP AZ61 are both studied by tensile test with different temperatures(200℃ to 250℃) and strain rates(8.33×10-3sec-1,1.67×10-3sec-1 and 8.33×10-4sec-1). The relationship between texture distribution and mechanical properties of a FSP AZ61 alloy is discussed. In the microstructure of FSP AZ61 Mg alloys, Stir Zoon (SZ) has fine recrystallized grains. An intense basal plane texture detected by X-ray diffraction (XRD) roughly surrounded the rotation pin column after FSP. On tensile test, both of the AZ61-O and FSP AZ61 experimental results indicate that the serrations of stress-strain curve observed above 200℃ owing to the dynamic recrystallization (DRX). The ultimate stress, yield stress and uniform elongation of the specimens decreased with the increasing tensile temperature and decreasing strain rate. Total elongation increased as the tensile temperature increased and/or the strain rate decreased. According to the experiment results, all FSP AZ61 samples have better elongation than AZ61-O ones above 225℃. The reason why the elongation of FSP AZ61 alloys is less than AZ61-O at 200℃ is attributed to the deformation twins growing out of the tensile test more easily in FSP AZ61. This phenomenon is associated with the texture of FSP.
 DRX softened the structure and induced the diffused necking that is the domain reason to cause the decreasing of flow stress and increasing of elongation; thus the uniform elongation was reduced. The grain boundary sliding (GBS) which can be presented by the stress exponent(n) suppressed the DRX softening and local necking so that the total elongation tended to increase under the high temperatures and low strain rates.
中文摘要 I
Abstract III
總目錄 V
表目錄 VII
圖目錄 VIII

第一章 前言 1
第二章 文獻回顧 3
2-1 鎂合金分類記號與合金元素添加效應 3
2-2 摩擦攪拌銲接與摩擦攪拌製程原理 4
2-3 AZ61鎂合金摩擦攪拌製程後之組織特徵 5
2-4 鎂合金之變形行為 6
2-4-1 溫度效應 6
2-4-2 動態再結晶 6
2-4-3 晶界滑移 8
2-5 鎂合金拉伸性質與研究目的 8
第三章 實驗方法 14
3-1 材料製備與摩擦攪拌製程 14
3-2 微觀組織觀察 14
3-3 X-ray 繞射分析 15
3-4 微硬度測試 15
3-5 拉伸試驗 15
第四章 實驗結果 24
4-1 摩擦攪拌微觀組織 24
4-2 微硬度測試 24
4-3 X-ray繞射分析 25
4-4 拉伸測試 25
4-3-1 拉伸溫度效應 25
4-3-2 拉伸應變速率效應 27
4-3-3 FSP材拉伸速率及溫度效應綜合比較 28
4-4 拉伸破斷面觀察 29
第五章 討論 49
5-1 拉伸性質 49
5-2 動態再結晶 50
5-3 晶界滑移 52
第六章 結論 63
參考文獻 64
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