臺灣博碩士論文加值系統

中文摘要

台灣為世界自行車產業重要供應商之一，而作為一個生產的基地，必須要有生產製造技術優勢的掌握。至於自行車用材的演變，從碳鋼→鋁合金→碳纖維→鈦合金，便可看出業界追求更強更輕材料的渴望，而目前自行車市場的主流產品仍以鋁合金為主。鋁合金比重為2.7g/cm3，鎂合金比重為1.8 g/cm3，若產品結構尺寸不變，採用鎂合金則可降低33%的重量。而且鎂合金除了具低密度特性外，尚有優良的比強度、比剛性、切削性、制振性、吸震性、及可回收等特性。
目前自行車的結構產品如車架、手把、豎管、齒盤曲柄、座管、輪圈、剎車夾器等，經常使用的材料為經過T6處理的6061鋁合金。而本實驗所選用的AZ80A鎂合金的強度與其相當接近，且可擠製、鍛造、及銲接，並已實際使用在車架及前叉上。
本實驗將對AZ80A鎂合金擠製板，施以150、200、250℃三溫度時效處理，時效時間為0.5~128hr。並對時效試片進行機械性質測試、XRD繞射分析及破斷面檢視，希望能藉由時效製程的施作找出有效提升基材強韌特性析出相之最佳析出時程。
實驗結果顯示，試片經150℃、短時效處理，便出現沿晶界向晶粒內部析出成長之不連續層狀析出物，且隨時效時間的增長此層狀析出物的析出增多，對硬度值及最大拉伸強度值的提升有明顯助益，但對伸長率卻有不良的影響。
於200℃極短時效(0.5hr)試片，已觀察到層狀析出物的生成，且隨時效時間的增長、析出物量將持續增多；在時效8hr之後，草蓆狀析出物將從未變態之晶粒內部均勻析出，此時之硬度值稍微降低外，降伏強度與最大拉伸強度並未產生明顯的變化；而在時效32hr之後，板片狀析出物亦從晶粒內部均勻析出，但此析出相比例僅佔少量，故無法判斷其對機械性質的影響。
於250℃，在短時效時間便有不連續層狀析出物和邊界析出物的開始析出，此時硬度值、最大拉伸強度及伸長率皆有所提升；但從時效4hr開始，晶粒內部開始有短棒狀析出物的析出，且邊界析出物亦會隨之增加，發現除了硬度值無明顯變化外，最大拉伸強度與伸長率皆隨著時效時間的增長而呈現緩緩下降的情形。
建議若要對AZ80A鎂合金擠製板行時效處理，可選擇時效溫度200℃、時效時間8~16hr之熱處理製程，能夠得到良好之硬度值與最大拉伸強度、且伸長率亦不差的性質。最後希望藉由本次研究的成果，能對自行車業界和工業界的熱處理技術的提升有所助益，使鎂合金能在更多領域上有更廣泛的應用。

ABSTRACT

Taiwan is one of the most important bicycle suppliers in the world. As a base of production, there must be a mastery of advantages of manufacturing technology. In the respect of the evolution of bicycle materials from early carbon steel, then aluminum alloy, then carbon fiber, and the current titanium alloy, it is apparent that the traders’ eager desire to find the stronger and lighter materials. Aluminum alloys still dominates the manufacturing of bicycles. The specific gravity of aluminum alloy is about 2.7 g/cm3 and the magnesium alloy is only at 1.8 g/cm3. If product structure size is still remained the same, a use of magnesium alloy can result in 33% reduction of the weight. Not only enjoying low density, magnesium alloy characterized with good specific strength, specific rigidity, machinability, restrict vibration, damping capacity, and recyclability.
Aluminum alloy 6061 undergoing T6 treatment has been used frequently in component for bicycles such as frame, handle bar, stem, chain-wheel, seat tube, wheel rim, and brakes. The strength of AZ80A magnesium alloy selected for this experiment is similar to that of T6-treated 6061aluminum alloy that can be extruded, forged and welded and is already used in frame and front-fork.
In this experiment, we carried out the tri-temperature aging treatment at 150, 200, 250℃ on the extruding AZ80A magnesium alloy, with the aging time ranging from 0.5 hr to 128 hr. We also worked on tensile test, micro-hardness test, x-ray diffraction analysis and analyzing the fracture surface. Hopefully, we can through the implementation of aging process to find the best precipitating mechanism which can enhance the precipitate phase and resilient characteristics for base metal effectively.
Findings of the experimental show that the extruding sheet of AZ80A magnesium alloy produces the discontinuous layer-shaped precipitates that grow form grain boundary into interior with short aging time at 150℃temperature. These layer-shaped precipitates will continue to increase with the lengthening aging time that brings marked improvement to micro-hardness and ultimate tensile strength but, on the contrary, shows poor influence to elongation.
When conducting the short-time aging treatment under 200℃, the generation of layer-shaped precipitates is witnessed, and the amount of precipitates also increase gradually with increasing the aging time. After 8 hours aging, mat-shaped precipitates will be precipitated evenly in untransformed grains, there appears no significant change for yield strength and tensile strength except for a slight decrease of micro-hardness. After 32 hours aging, lath-shaped precipitates precipitated inside the grain, with the meager volume cannot determine the influence of mechanical properties.
When conducting under 250 ℃, in short aging time specimen, we can observe the discontinuous layer-shaped precipitates and boundary precipitates start to precipitate with the micro-hardness, ultimate tensile strength and elongation to be improved. While at 4hr aging, however, short-rod-shaped precipitates begin to precipitate evenly interior the grain, and boundary precipitates keep growing. Tensile strength and elongation are decreased slowly with increasing the aging time, except the micro hardness is still maintained constant.
Our suggestion for thermal treatment of AZ80A magnesium alloy is selecting 200℃aging temperature and 8~16 hr aging time can achieve the better micro-hardness and tensile strength as well as not-so-poor elongation. We expect findings of this research will be helpful to the heat treatment techniques of the bicycle industry and the industry in the hope of making magnesium alloy more extensively applicable in more areas.
Key Words: AZ80A Magnesium Alloy, Aging Treatment, Layer-Shaped Precipitates, Mat-shaped Precipitates, Lath-shaped Precipitates, Boundary Precipitates, Short-Rod-Shaped Precipitates.

目錄

封面內頁
簽名頁
授權書…………………………………………………………………………………….. iii
中文摘要………………………………………………………………………………….. iv
英文摘要………………………………………………………………………………….. vi
誌謝……………………………………………………………………………………….. ix
目錄……………………………………………………………………………………….. x
圖目錄…………………………………………………………………………………….. xiv
表目錄…………………………………………………………………………………….. xviii

第一章 序論……………………………………………………………………………. 1
1.1 前言……………………………………………………………….. 1
1.2 鎂合金的應用範圍與其未來的發展……………………………. 4
1.3 本文目標………………………………………………………….. 7
第二章 文獻回顧………………………………………………………………………. 8
2.1 鎂合金的簡介…………………………………………………….. 8
2.2 鎂合金的命名…………………………………………………….. 9
2.3 鎂合金的分類…………………………………………………….. 10
2.3.1 鑄造用鎂合金…………………………………………. 10
2.3.2 鍛造用鎂合金…………………………………………. 12
2.4 合金元素的添加對鎂合金性質的影響…………………………. 13
2.4.1 添加銀(Ag)元素的影響…………………………….. 13
2.4.2 添加鋁(Al)元素的影響…………………………... 13
2.4.3 添加鈹(Be)元素的影響…………………………….. 14
2.4.4 添加鈣(Ca)元素的影響…………………………….. 14
2.4.5 添加鋰(Li)元素的影響…………………………... 14
2.4.6 添加錳(Mn)元素的影響……………………………. 14
2.4.7 添加矽(Si)元素的影響…………………………... 14
2.4.8 添加錫(Sn)元素的影響…………………………….. 15
2.4.9 添加鋅(Zn)元素的影響…………………………….. 15
2.4.10 添加鋯(Zr)元素的影響………….............. 15
2.4.11 添加稀土元素(R.E.)元素的影響……………….... 15
2.4.12 添加鐵(Fe)、鎳(Ni)、銅(Cu)、鉻(Cr)元素的影響16
2.5 鎂合金的材料特性……………………………………………….. 16
2.5.1 比強度/比剛性佳……………………………………… 16
2.5.2 電磁波遮蔽性佳………………………………………. 17
2.5.3 吸震性佳…………………………………………….. 18
2.5.4 材料之可回收性佳……………………………………. 18
2.5.5 熱傳散熱性佳…………………………………………. 19
2.6 鎂合金之時效析出研究…………………………………………. 19
2.6.1 鎂合金析出物之析出形態……………………………. 21
2.6.2 鎂-鋁-鋅系鎂合金的析出形態…………………….. 22
2.6.3 鎂合金析出物之顯微組織……………………………. 25
2.6.4 析出強化理論…………………………………………. 33
2.6.5 析出物量對機械性質的影響…………………………. 34
第三章 實驗方法………………………………………………………………………. 38
3.1 實驗材料………………………………………………………….. 38
3.2 實驗規劃………………………………………………………….. 39
3.3 實驗步驟………………………………………………………….. 40
3.4 顯微組織的觀察與分析………………………………………….. 42
3.5 拉伸實驗………………………………………………………….. 44
3.6 微硬度實驗……………………………………………………….. 45
3.7 晶粒尺寸的量測………………………………………………….. 46
3.8 掃描式電子顯微鏡(SEM)與能量分散光譜儀(EDS)……………. 47
3.9 X光繞射儀(X-ray Diffraction)分析……………………... 48
第四章 結果與討論……………………………………………………………………. 49
4.1 析出物相之定義………………………………………………….. 49
4.1.1 層狀析出物………………………………………….. 50
4.1.2 草蓆狀析出物……………………………………….. 50
4.1.3 板片狀析出物……………………………………….. 51
4.1.4 邊界析出物與短棒狀析出物…………………………. 51
4.2 經時效處理之試片顯微結構組織的改變………………………. 56
4.2.1 溫度為150℃之時效處理…………………………... 56
4.2.2 溫度為200℃之時效處理…………………………... 60
4.2.3 溫度為250℃之時效處理…………………………... 59
4.3 XRD繞射分析………………………………………………………. 64
4.4 時效處理與機械性質之關連性…………………………………. 68
4.4.1 時效處理對晶粒尺寸的影響…………………………. 68
4.4.2 時效處理對微硬度值的影響…………………………. 68
4.4.3 時效處理對降伏強度的影響…………………………. 71
4.4.4 時效處理對最大拉伸強度的影響……………..... 73
4.4.5 時效處理對伸長率的影響……………………………. 75
4.4.6 時效處理對韌性值的影響……………………………. 77
4.5 析出物之析出量與機械性質的關連性…………………………. 79
4.5.1 析出物析出量與時效時間之關係……………………. 79
4.5.2 析出物析出量與硬度值之關係………………………. 79
4.5.3 析出物析出量與降伏強度之關係……………………. 82
4.5.4 析出物析出量與最大拉伸強度之關係………………. 82
4.5.5 析出物析出量與伸長率之關係………………………. 82
4.5.6 析出物析出量與韌性值之關係………………………. 86
4.6 時效試片破斷面的分析………………………………………….. 86
第五章 結論……………………………………………………………………………. 102
第六章 參考文獻………………………………………………………………………. 104

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