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| 題名: | 熱處理、銅/鎂比與合金元素(鈧、鋯、鑭與鈰)對於Al-4.6Cu-Mg-Ag合金微結構與機械性質之影響;Effects of Heat Treatment, Cu/Mg Ratio and Alloying Elements (Scandium, Zirconium, Lanthanum and Cerium) on the Microstructures and Mechanical Properties of Al-4.6Cu-Mg-Ag alloys |
| 作者: | 陳裕德;Chen,Yu-Te |
| 貢獻者: | 機械工程學系 |
| 關鍵詞: | Al-4.6Cu-Mg-Ag合金;銅/鎂比;自然時效;冷加工;稀土元素;過渡元素;介金屬化合物;Al-4.6Cu-Mg-Ag alloy;Cu/Mg ratio;natural aging;cold working;rare earth;transition element;intermetallic compounds |
| 日期: | 2015-08-06 |
| 上傳時間: | 2015-09-23 15:12:56 (UTC+8) |
| 出版者: | 國立中央大學 |
| 摘要: | Al-4.6Cu-Mg-Ag為一可熱處理型鋁合金，主要析出強化相為Ω與θ’相，Ω相由於在鋁的主要滑動面{111}α上析出且熱穩定佳，使合金具有極為優良的常溫與高溫(200℃以下)強度以及熱穩定性，廣泛運用於航太與軍事工業。合金中Mg、Ag原子聚集(Mg-Ag cluster)與差排，分別是Ω相與θ’相的析出成核點，此外合金之銅/鎂比影響析出相的種類(Ω、θ’與S’相)與分布情形，故於銅成分固定下之合金，鎂含量為影響Ω相析出的重要合金元素，而θ’相的析出行為則受加工與差排所影響。此外，合金固溶處理後基地內溶質原子固溶量，亦將造成Ω與θ’相析出特性之變化。
自然時效過程中產生Mg-Ag聚集，將有利於Ω相析出，而冷加工使材料內部產生大量差排，不僅增加θ’相析出成核點而促進θ’相析出外，又會阻擋原子擴散抑制Mg-Ag聚集，減少Ω相析出。為了進一步瞭解Mg-Ag聚集、差排及合金元素對Al-4.6Cu-Mg-Ag鋁合金強化相析出之影響，因此本論文首先將藉由T7與T8兩種熱處理，調整「自然時效時間」與「冷加工量」，探討熱處理與冷加工對於不同Cu/Mg比之Al-4.6Cu-Mg-0.5Ag合金微結構與機械性質之影響。再者，藉由微量合金元素鈧(Sc)、鋯(Zr)、鑭(La)與鈰(Ce)添加於Al-4.6Cu-0.3Mg-0.6Ag (A201)合金中，探討稀土、過渡元素對於合金微結構、晶粒尺寸、析出特性與機械性質之影響。文中完整說明製程、微結構與性質三者間之相對關係，以呈現此高強度鋁合金之特性。
本論文透過光學顯微鏡(Optical Microscopy)、電子微探儀(Electron Probe X-ray Microanalysis)、微差掃描熱分析(Differential Scanning Calorimetry)、導電度(Electrical Conductivity, %IACS)及穿透式電子顯微鏡(Transmission Electron Microscopy)等進行微結構觀察與分析，並搭配硬度與拉伸性質試驗以瞭解機械性質之變化，獲得以下結論：自然時效對於Al-4.6Cu-Mg-0.5Ag合金析出量與機械性質並無顯著影響，但可提升合金於人工時效初期之析出動力與強化速度。冷加工促進θ’相而抑制Ω相析出，於高Cu/Mg比之合金中或隨冷加工量增加上述現象更為明顯，使得合金總析出量及機械強度提升，但卻造成延性降低。添加微量合金元素後，因Al3Sc、Al3(ScxZr1-x)、W(Al8.5-4Cu6.6-4Sc)相、富鑭與富鈰相生成，雖有助於合金晶粒細化，但W相、富鑭與富鈰相等介金屬化合物無法藉由固溶處理回溶至基地中，減少基地內Cu、Mg等原子固溶量，造成Ω與θ’相析出量減少，並且延緩強化相之析出，不利於A201合金之機械強度。
;The main precipitation strengthening phases of heat treatable Al-4.6Cu-Mg-Ag alloys are Ω and θ’. The thermal stable Ω phase precipitates on the {111}α planes, the primary slip planes of the aluminum alloy and possess excellent mechanical strength under 200℃. Al-4.6Cu-Mg-Ag alloys are widely applied for moderate-temperature and high-strength applications in the aviation and military industries because of their excellent strength and thermal stability. The Mg-Ag clusters and the dislocations are the nucleation sites of Ω and θ’. The Cu/Mg ratio affects the relative distribution of Ω, S’ and θ’ phases, and influences the thermal stability of Al-4.6Cu-Mg-Ag alloys. The concentration of magnesium is an important factor for precipitation of Ω phase. The cold working introduces numerous dislocations and increases the heterogeneous nucleating sites of θ’ phase. Moreover, the precipitation characteristics of Ω and θ’ phases are also affected by solid solubility of the alloying elements in the matrix.
The Mg-Ag clusters form during natural aging and encourage the precipitation of Ω phase. The cold work introduces lots of dislocations and benefits for the precipitation of θ’ phase, but depresses the formation of Mg-Ag clusters. In order to interpret how the Mg-Ag clusters, dislocations and alloying elements influence the strengthening phases of Al-4.6Cu-Mg-0.5Ag alloy, hence, present works attempt to examine the effects of heat treatment and cold working on the microstructures and mechanical properties of different Cu/Mg ratio alloys, and start with various natural aging period and cold working percentages, subsequently heat treated to T7 and T8. Further, the other purpose of this investigation is to examine the effects of rare earth (scandium, lanthanum, cerium) and transition elements (zirconium) on the microstructures, grain sizes, precipitation specifics and mechanical properties of Al-4.6Cu-
0.3Mg-0.6Ag (A201) after T7 heat treatment. To completely explain the relationship among the process, structure and property, then the features of this high strength aluminum alloy can been understood completely.
The relative microstructure variations were elucidated by the observations of optical microscope (OM), Electron probe X-ray microanalysis (EPMA), differential scanning calorimeter (DSC), electrical conductivity meter (%IACS), transmission electron microscopy (TEM). Mechanical properties were correlated with Rockwell hardness and tensile testing. The results showed that natural aging treatment has little noticeable benefit on the quantity of precipitation strengthening phases and mechanical properties, but it increases the precipitation strengthening rate at the initial stage of artificial aging. Cold working brings more lattice defects and suppresses the precipitation of Ω phase but encourages the θ’ phase. The above-mentioned precipitation phenomena are more obvious in high degrees of cold working and high Cu/Mg ratio alloy. More θ’ phases precipitate and increase the strength, but decrease the ductility. Adding the alloying elements of Sc, Zr, La and Ce to A201 alloys, the Al3Sc, Al3(ScxZr1-x), W(Al8.5-4Cu6.6-4Sc), La-rich and Ce-rich intermetallic compounds form, and the W, La-rich and Ce-rich phase can’t dissolve to matrix, reducing effective quantity of Cu and Mg atoms in α-matrix, disadvantaging the precipitation of Ω and θ’ phases. Although the grain refinement is obtained by the addition of alloying elements, the decrease of strengthening phases lowers the strength but promotes the ductility of A201 alloys. |
| 顯示於類別: | [機械工程研究所] 博碩士論文
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