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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Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/82908

Title:	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
Authors:	劉京鑫;Liu, Ching-Hsin
Contributors:	機械工程學系在職專班
Keywords:	鋁合金;7055;熱處理;擠型;Aluminum;7055;heat treatment;extrusion
Date:	2020-01-20
Issue Date:	2020-06-05 17:42:32 (UTC+8)
Publisher:	國立中央大學
Abstract:	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。 ;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.
Appears in Collections:	[Executive Master of Mechanical Engineering] Electronic Thesis & Dissertation

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