Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/9831
標題: On the Mechanism of Grain Growth of the Deformed 2024 Al-Cu-Mg Alloy Plate after Annealing Heat Treatment
退火熱處理對加工後2024Al-Cu-Mg合金軋延板料晶粒成長機構之探討
作者: 楊伯文
Yang, Po-Wen
關鍵字: 2024 Aluminum Alloy;2024鋁合金;grain growth;solution heat treatment;晶粒成長;固溶熱處理
出版社: 材料科學與工程學系所
摘要: 
飛機前、後機身蒙皮所使用之材料以2024鋁合金軋延板料居多,於拉伸成形時偶爾會出現粗晶現象。本實驗利用厚度為2.29 mm之2024鋁合金軋延板料製成初始狀態為O料及T4料之試片,使試片經不同的拉伸變形量、退火及固溶熱處理等多種實驗組合,觀察其晶粒大小的變化,以探討何種因素導致2024鋁合金軋延板在拉伸變形過程中發生晶粒異常成長。
在實驗中經EBSD(Electron Back-Scatter Diffraction)觀察後得知O料與T4料試片顯微組織傾向{001}的織構。O料試片經5%-20%之拉伸變形後再經退火且固溶熱處理,與夾持區域相較,發現變形量5%時無晶粒成長發生,變形量10%時晶粒發生最大成長,其在晶粒短軸向及晶粒長軸向之晶粒大小分別約為夾持區域的4.3及3.1倍,且成長後之晶粒外形為非等軸晶,於變形量15%及20%時晶粒反而縮小並漸趨近於夾持區域之晶粒大小;故若使2024鋁合金軋延板O料試片避開約10%之拉伸變形量,可避免晶粒粗大化。
另由拉伸應力-應變圖得知,需施加於T4料試片的拉伸應力約為O料試片2倍,且T4料拉伸變形10%試片由TEM(Transmission Electron Microscopy)觀察發現有高密度的差排存在鋁基地內,但實驗結果T4料試片經5%-20%的拉伸變形再經退火且固溶熱處理後,其晶粒大小及形狀卻幾乎無改變。
再者,T4料及O料試片經拉伸變形10%時,可使其相鄰晶粒彼此往兩晶軸向拉近的方向變形,由TEM試片之觀察,T4料試片的塑性變形集中在晶界附近,而O料試片則在晶界附近及晶粒內部皆有塑性變形;由推演認為當一晶粒之塑性變形是遍及整個晶粒時,則此塑性變形可成為此晶粒調整其晶軸向的驅動力。綜合以上觀察結果, O料試片於拉伸變形10%後再經退火且固溶熱處理時,存在著一種機構,是藉由兩相鄰晶粒的晶軸向已被拉近,並受常溫變形時所累積的應變能與晶界之表面能降低的驅動力作用下,使具高能量狀態之晶界處的差排,在高溫下經由相互抵消、重新排列而消除,使得晶界兩旁的晶粒亦隨之合併成長。

Most of the materials used for an airplane's front and rear fuselage skins are the 2024 Aluminum Alloy rolled plate material, which sometimes has the phenomenon of overgrowth of crystals when being stretched to take shape. In this experiment, the 2024 Aluminum Alloy Rolled Plate material in the thickness of 2.29 mm was applied to create the trial pieces whose initial statuses were the O material and the T4 material. We made the trial pieces undergo many kinds of experimental combinations such as different amounts of stretch and deformation, annealing, and solution heat treatment, so as to observe the changes of its sizes of crystal grains, in order to explore what factors result in the abnormal growth of 2024 Aluminum Alloy Rolled Plate during the process of stretch and deformation.
In this experiment, Besides, through the observations via EBSD (Electron Back-Scatter Diffraction), we knew the microstructure-oriented {001} texture and structure of the trial pieces of O material and T4 material. When the trial pieces of O material received annealing and solution heat treatment after undergoing 5%-20% of stretch and deformation, compared with the gripping area, no occurrence of the growth of its crystal grains would appear when the amount of stretch and deformation was 5%; the maximum growth would appear when the amount of stretch and deformation was 10%, and the vertical and transverse sizes of the crystal grains were respectively 4.3 times and 3.1 times greater than that of the gripping area. Also, the appearance of the crystal grains after the growth was non-equiaxed crystal. When the amount of stretch and deformation was 15% or 20%, the crystal grains would shrink contrarily and get close to the size of the crystal grains in the gripping area. Therefore, if we make the O material of the 2024 Aluminum Alloy Rolled Plate avoid 10% of the amount of stretch and deformation, we can ward off the overgrowth of crystals.
In addition, through the Stretch Stress Strain Diagram, we knew that the stretch stress necessary to be imposed on the trial piece of T4 material was about 2 times greater than that on the O material. Besides, from the observations on the trial piece of T4. material with 10% of stretch and deformation via TEM(Transmission Electron Microscopy), we found that high-density dislocations exist in the aluminum base. However, the experiment results showed that the sizes and shapes of the T4 material's crystal grains nearly have no changes after the T4 material had undergone 5%-20% of stretch and deformation and then received annealing and solution heat treatment.
Furthermore, after the T4 material and the O material underwent 10% of stretch and deformation, their neighboring crystal grains would deform in the two closer crystal axial directions each other. Through the observations on the trial pieces via TEM, the T4 material had plastic deformation centering on the crystal boundary, while the O material had plastic deformation both around the crystal boundary and within the crystal grains. Judging from deduction, we consider: When the plastic deformation of a crystal grain spreads all over the crystal grain, such a plastic deformation can be the thrust of the crystal grain to adjust its crystal axial direction. To sum up the observation results mentioned above, when the O material receives annealing and solution heat treatment after undergoing 10% of stretch and deformation, a certain mechanism will appear, in which, There exists a mechanism including adjustions of neighboring grain axis, the driving force of the strain energy as deformation in room temperatureand surface energy decrease of grain boundaries. It leads to the dislocations by the grain boundaries offset mutually and eliminate by rearrangment.The grains by the side of dislocations combine to grow.
URI: http://hdl.handle.net/11455/9831
Appears in Collections:材料科學與工程學系

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