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Title: | AA2050 鋁合金差排與析出物之交互作用關係探討 Dislocation-precipitate Interaction of AA2050 Aluminum Alloy |
Authors: | 朱芊瑜 Chien-Yu Chu |
Advisor: | 楊哲人 Jer-Ren Yang |
Keyword: | AA2050鋁銅鋰合金,析出硬化,T1相,奈米級析出物,顯微結構,穿透式電子顯微鏡, AA2050 Al-Cu-Li alloys,precipitation hardening,T1 phase,nanoscale precipitates,microstructure,transmission electron microscope, |
Publication Year : | 2022 |
Degree: | 碩士 |
Abstract: | AA2050鋁銅鋰合金展現出高強度、輕量化和良好的耐蝕性等優異性能,因此非常適合應用於航空材料。在AA2050鋁合金中,強化效果的貢獻主要來自T1相的析出,該析出相在母相基地的{111}Al面上以盤狀結構形式存在於鋁合金材料內部。本研究聚焦於AA2050鋁銅鋰合金之析出物T1與差排間的交互作用,有關T1析出物的強化機制和析出物與差排之交互作用已在過去文獻中有過多次討論,最早T1析出物被視為一種強大的不可剪切相,然而當時受限於穿透式電子顯微鏡之影像解析度,無法進一步觀測厚度僅有數奈米的T1析出物。隨著高解析電子顯微鏡技術的進步,漸漸有許多研究發現T1在足夠薄的厚度下會出現被差排剪切的現象,推翻了過去T1無法被差排剪切的結論。本研究首先透過硬度試驗找出AA2050鋁合金之最佳人工時效條件為155℃持溫20小時,並將此頂時效狀態的試片進行常溫及高溫(150℃、200℃)拉伸試驗測定其機械性能,發現於高溫狀態下材料仍保有一定的強度。針對析出物與差排交互作用之顯微結構,本研究透過穿透式電子顯微鏡的拍攝TEM明場影像及HRTEM影像取得差排剪切的T1之形貌,進一步發現在不同應變量下,析出物T1與差排的交互作用隨著應變量提升而有漸增的趨勢,且差排對T1同一處僅會進行單一次剪切。值得注意的是,對於同一T1析出物而言,每一次剪切事件發生之間距在常溫下為2至5奈米,而高溫拉伸試片中觀測到的交互作用情形相較於常溫拉伸試片更加劇烈,被剪切的T1之形貌更加不規則,剪切現象的發生更加頻繁密集。此外,本研究也透過EDS mapping發現T1析出物周遭出現鎂銀元素偏析,T1析出物內部也有少量鋅原子取代銅原子的現象發生。 AA2050 Al-Cu-Li alloys are widely used in aerospace industries due to their high strength, low density and good damage tolerance. Among AA2050 aluminum alloys, the precipitation of T1 phase provides the main contribution of strengthening. T1 phase is identified as platelet-shaped precipitate, lying on habit planes of {111}Al in the aluminum matrix. In this work, the dislocation interactions with T1 phase in AA2050 Al-Cu-Li alloy have been investigated. In early studies, considerable effort has been devoted to the relationships between dislocations and T1 precipitates. T1 precipitates were initially considered as non-shearable particles, while subsequent researches gave solid evidence that sufficiently thin nanoscale T1 precipitates could be cut through by moving dislocations. In this study, hardness test was first conducted, determining 155℃ artificial aging treatment for 20 hours as part of the experimental design to acquire the peak aging condition of AA2050 aluminum alloy. Room temperature and high temperature (150℃ and 200℃) tensile tests were employed on the peak-aged samples, and the experimental results elucidated that AA2050 aluminum alloy retained its desirable mechanical properties to such a degree at elevated temperatures. As the interactions with dislocations increased with the increment of strain, conventional TEM bright-field images and HRTEM images demonstrated the morphology of T1 precipitates cut by dislocations under different plastic deformation stages. Observations of the microstructures of the specimens indicated that single shearing events were energetically preferred regardless of the thicknesses of T1 precipitates. It is worth noting that the distance between every single shearing step falls in a range of 2-5 nm for room temperature tensile test specimens. However, it is of interest to evaluate more precisely on those high temperature tensile test samples since the phenomena of the dislocation-precipitate interactions observed were relatively more complex and individualized. Moreover, this research also revealed the segregation of Mg and Ag atoms surrounding T1 precipitates, and a minor occurrence of Zn atoms substituting Cu atoms within the T1 precipitates through EDS mapping. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/89935 |
DOI: | 10.6342/NTU202303875 |
Fulltext Rights: | 同意授權(全球公開) |
Appears in Collections: | 材料科學與工程學系 |
Files in This Item:
File | Size | Format | |
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ntu-111-2.pdf Until 2028-08-09 | 5.71 MB | Adobe PDF |
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