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; Influence of homogenization temper and aged temper on the fatigue behavior of aerospace aluminum alloy

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Title:	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;Influence of homogenization temper and aged temper on the fatigue behavior of aerospace aluminum alloy
Authors:	邱鼎為;Ding-Wei Chiu
Contributors:	機械工程研究所
Keywords:	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;Aluminum alloy 7075;Aluminum alloy 7050;Aged temper;Bridge;Crack closure;PFZ;Homogenization;Solution
Date:	2004-06-28
Issue Date:	2009-09-21 11:45:39 (UTC+8)
Publisher:	國立中央大學圖書館
Abstract:	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.
Appears in Collections:	[Graduate Institute of Mechanical Engineering] Electronic Thesis & Dissertation

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