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研究生:邱鼎為
研究生(外文):Ding-Wei Chiu
論文名稱:均質化處理及時效處理條件對航空用鋁合金金屬疲勞舉動之影響
論文名稱(外文):Influence of homogenization temper and aged temper on the fatigue behavior of aerospace aluminum alloy
指導教授:歐炳隆
指導教授(外文):Bin-lung Ou
學位類別:碩士
校院名稱:國立中央大學
系所名稱:機械工程研究所
學門:工程學門
學類:機械工程學類
論文種類:學術論文
論文出版年:2004
畢業學年度:92
語文別:中文
論文頁數:65
中文關鍵詞:時效處理無析出空乏帶裂縫閉合效應架橋效應均質化處理7050鋁合金7075鋁合金
外文關鍵詞:Aluminum alloy 7075Aluminum alloy 7050Aged temperBridgeCrack closurePFZHomogenizationSolution
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本研究主要以7075與7050航空用鋁合金為實驗材料,探討不同熱處理條件所呈現之疲勞裂縫成長特性。
  實驗中藉由改變均質化參數、固溶參數、時效處理參數以及R值,並配合光學顯微鏡(OM)、掃描式電子顯微鏡(SEM)、掃描穿透式電子顯微鏡(TEM)、動態材料試驗機作分析,研究影響疲勞裂縫成長特性之因數,搭配合金已知的拉伸性質與應力腐蝕效應,可作為航空材料選用之重要依據。
  由實驗結果得知,當R=0.1時,若合金採階段性均質化處理(Step-H),則在應力強度因數差值小時(△K<16MPa ),合金擁有較小之降伏強度、非整合型的析出物以及晶界周圍擁有較寬之無析出空乏帶(PFZ)時,可以得到較佳之裂縫成長特性,但必須考慮階段性淬火促進異質成核導致基地弱化的影響,在△K大時,影響裂縫成長的效應隨之減弱使裂縫成長曲線相仿。當施以H470均質化時,可以得到較大之再結晶晶粒與較高比例之再結晶,而在大晶粒的情況下不同時效處理之裂縫成長曲線幾乎重合,另外,較大之晶粒在裂縫成長時其破斷面較為粗糙,會引發裂縫閉合效應而減緩裂縫的延伸。當R=0.8時,不同熱處理對於裂縫成長特性的影響大幅減少,會得到幾乎一致的成長曲線。此外,7075合金由於形成之分散相E phase較7050合金之分散相Al3Zr粗大,當裂縫在成長時會有架橋效應的產生,阻礙裂縫的前進,因此7075呈現較7050合金為佳的裂縫成長特性。
A program of experimental and analytical tasks has been conducted to discuss the relationship between heat treatment and fatigue crack propa-
gation(FCP)in an aluminum aerospace alloy 7075 and 7050.
The experiment was investigated via different homogenization, solution, aging condition and load ratio. The influence of fatigue crack pro-
pagation was characterized and analyzed by using optical microscopy (OM), scanning electron mic-
roscopy (SEM), transmission electron microscopy (TEM) and Instron Model 8800 Testing System. The basis of airframe structural application is the result of experiment combining with tensile pr-
operties and stress corrosion cracking effect.
The result indicate that the alloys received step-homogenuzation(Step-H) have higher resistanc to fatigue crack growth with lower yielding st-
ress, incoherent precipitation and wider PFZ when a stress ratio (R) is 0.1 and △K is small. But it can get similar fatigue crack growth rates in all aged temper condition with increasing △K. When the alloys were given H470, it can obtain the highest fraction of recrystallization and
larger grain size. Alloys with larger grain size will get almost the same fatigue crack growth rates in all heat treatment and it also occur roughness-induced closure for the mis-match of fracture surface.The aluminum alloy 7075 will percipates coarse Al3Zr dispersoids and can bri-
ges the surface cracks resulting in retarding crack propagation, hence the alloy 7075 can get better resistance of crack propagation than the alloy 7050.
目 錄
頁次
Abstract……………………………………………Ⅰ
摘要…………………………………………………Ⅱ
目錄…………………………………………………Ⅲ
表目錄………………………………………………Ⅳ
圖目錄………………………………………………Ⅴ
第一章 緒論
一、序言 1
二、理論基礎與文獻回顧…………………………2
2.1 7000系鋁合金之時效析出序列………………2
2.2 淬火敏感性(Quench Sensitivity)…………4
2.3 再結晶與分散粒子……………………………6
2.3.1 再結晶的機構 ………………………………6
2.3.2 分散粒子對再結晶的影響…………………7
2.4 疲勞性質探討…………………………………10
2.4.1 疲勞機制……………………………………10
2.4.2 疲勞的影響機構……………………………11
2.5 裂縫閉合現象…………………………………12
2.6 氫致脆裂機構…………………………………12
第二章 本文………………………………………14
一、前言……………………………………………14
二、實驗步驟與方法 ………………………………16
2.1 材料……………………………………………16
2.2 製程……………………………………………16
2.3 拉伸試驗(Tensile Test)…………………17
2.4 疲勞裂縫成長試驗……………………………17
2.5 金相及疲勞裂縫路徑之觀察(OM)…………18
2.6 掃描式電子顯微鏡觀察(SEM)………………18
2.7 掃描穿透式電子顯微鏡(TEM)………………19
三、結果與討論……………………………………20
3.1 不同熱處理條件下之顯微結構………………20
3.1.1 均質化對於微結構的影響…………………20
3.1.2 固溶時效處理對於微結構的影響…………21
3.2 不同熱處理條件下之拉伸性質比較…………21
3.3 熱處理對於疲勞裂縫成長特性之影響………22
3.3.1 R=0.1時疲勞裂縫成長之特性………………22
3.3.2 R=0.8時疲勞裂縫成長之特性………………25
四、結論……………………………………………28
五、參考文獻………………………………………30
表……………………………………………………35
圖……………………………………………………37
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