熱處理與熱擠型參數對AA7055合金微結構與相關性質之影響

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劉京鑫(Ching-Hsin Liu) 查詢紙本館藏

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機械工程學系在職專班

論文名稱

熱處理與熱擠型參數對AA7055合金微結構與相關性質之影響
(Effects of Heat-Treatment and Hot Extrusion Parameters on the Microstructures and Relevant Properties of AA7055 Alloys)

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摘要(中)

本研究以光學顯微鏡(OM)、電子微探儀(FE-EPMA)、導電度量測儀(Electrical conductivity tester)、電子顯微鏡(TEM、SEM)等分析Al-8.0Zn-2.1Mg-2.3Cu-0.16Zr (AA7055)高強度鋁合金微結構，並以硬度及拉伸試驗，探討不同時效製程對AA7055鋁合金微結構與機械性質之影響；同時也藉由剝蝕腐蝕試驗，探討其抗應力腐蝕之能力。另外，也藉由熱擠型參數(擠型比、擠型速度、預熱溫度等)之改變，來探討AA7055合金之熱擠型性。
研究結果顯示，鑄態微結構中，含有與鋁形成共晶的η (Mg(ZnCu)2)、T (Al2Mg2Zn3-Cu)、S (Al2CuMg-Zn)及θ (Al2Cu)四個相，其中以η (Mg(ZnCu)2)相為主；經均質化處理能有效消除(η+T)相，僅有微量S相與富鐵相Al7Cu2Fe會被殘留下來。利用兩段式均質化處理，可以有效提升鑄態合金之均質化溫度。當擠型比愈大、擠型速度愈高時，熱擠型的安全擠型面積會縮小，造成擠型件的過燒現象。
另外，AA7055在T651態時，具有最佳機械強度，而T7351態則具有最佳抗剝蝕腐蝕能力，且經T7651及T7751 (RRA) 兩種時效熱處理，其導電度、拉升機械性質均能滿足航太AMS 4337之規範，剝蝕腐蝕也能滿足ASTM G34-13之規範。

摘要(英)

In this study, the microstructures of Al-8.0Zn-2.1Mg-2.3Cu-0.16Zr (AA7055) high-strength aluminum alloys are analyzed using optical microscopy (OM), field-emission-electronic-micro-probe (FE-EPMA), conductivity measurement instrument, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Hardness and tensile tests are conducted to study the effects of aging process on the microstructure and mechanical properties of the alloy. Corrosion test is carried out to investigate its resistance to stress corrosion. The hot extrusion formability of AA7055 alloy is also investigated by the change of processing parameters (extrusion ratio, extrusion speed, temperature, etc.).
The results show that the as-cast microstructure contains η (Mg(ZnCu)2), T (Al2Mg2Zn3Cu), S (Al2CuMg-Zn), and θ (Al2Cu) phases which are eutectic with aluminum. The dominant phase is η (Mg(Zn-Cu)2). Homogenization treatment can effectively eliminate (η+T) phases as only trace S-phase and iron-rich phase (Al7Cu2Fe) are retained. Two-stage homogenization treatment is able to elevate the homogenization temperature of the as-cast alloy. When the extrusion ratio is larger and the extrusion speed is higher, the safe extrusion region of the hot extrusion is reduced, resulting in over-burning of the extruded part.
In addition, AA7055 has the best mechanical strength in the T651 temper and the best corrosion resistance in the T7351 temper. Both T7651 and T7751 (RRA) tempers show qualified electrical conductivity and tensile properties to meet the specifications of Aerospace AMS 4337 Standard, and exfoliation corrosion resistance to meet the ASTM Specification of G34-13.

關鍵字(中)

★ 鋁合金
★ 7055
★ 熱處理
★ 擠型

關鍵字(英)

★ Aluminum
★ 7055
★ heat treatment
★ extrusion

論文目次

摘要 I
Abstract II
總目錄 IV
表目錄 VII
圖目錄 VIII
一、前言 1
1.1鋁合金簡介與分類 1
1.2鋁合金的加工與熱處理代號 2
1.3高強度鋁合金之發展與應用 5
1.3.1 杜拉鋁 5
1.3.2 超杜拉鋁 6
1.3.3 超超杜拉鋁 7
1.4合金元素、加工製程與熱處理對高強度鋁合金性質之影響 9
1.4.1合金元素與均質化對再結晶之影響 9
1.4.1.1 微偏析元素的均質化 9
1.4.1.2 過飽和固溶元素的的析出 10
1.4.1.3 介穩相的相變化 10
1.4.2加工製程對再結晶之影響 11
1.4.3 Al-Zn-Mg-Cu合金之析出行為 12
1.4.4元素對Al-Zn-Mg-Cu合金機械性質與淬火敏感性之影響響 13
1.4.4.1鋅(Zn)對合金機械性質之影響 13
1.4.4.2銅(Cu)對合金機械性質與固溶溫度之影響 14
1.4.4.3鋯(Zr)對合金淬火敏感性之影響 15
1.5目前的合金規格 16
1.6 研究目的 19
二、實驗方法與步驟 20
2.1合金熔配 20
2.2均質化、熱擠型與時效熱處理 20
2.3機械性質測試 21
2.4剝落腐蝕試驗 21
2.5 微結構觀察與分析 …………………………………….……22
2.5.1 光學顯微鏡 ………………………………..……22
2.5.2 電子微探儀與X光繞射分析中間相 ……..……22
2.5.3 導電度與熱差掃瞄分析量測 ……………..……22
2.5.4 穿透式與掃描式電子顯微鏡 ………………… 23
三、結果與討論 24
3.1微結構分析 24
3.2均質化製程對微結構之影響 25
3.3擠型預熱溫度、擠型比與擠型速度對熱擠型件的影響 26
3.4.固溶時效熱處理對AA7055合金微結構、機械性質與剝蝕性質質之影響 27
3.4.1時效熱處理對再結晶之影響 27
3.4.2時效熱處理對晶界上η相之TEM微結構 28
3.4.3時效熱處理對導電度之影響 29
3.4.4時效熱處理對機械性質(硬度、拉升)之影響 30
3.4.5時效熱處理對剝蝕腐蝕之影響 30
四、結論 32
五、參考文獻 33

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指導教授

林志光(Chih-Kuang Kin)

審核日期

2020-1-20

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