臺灣博碩士論文加值系統

摘 要
鋁合金Al-Mg-Si-Cu具有高強度/重量比，因此廣泛應用在自行車車架的重要部位。6XXX系列鋁合金的主要合金元素為鎂及矽，同時也是最常用的熱處理型鋁合金。而為了得到更高的強度，在合金中加入元素Cu，成為Al-Mg-Si-Cu鋁合金並取代原本屬於Al-Mg-Si合金系的AA6061。
然而金相觀察目前所使用的鋁合金，觀察到晶粒粗大的現象。粗大晶粒的管件會導致冷作加工成型良率降低、加工後外表產生橘皮現象。目前透過退火製程解決成型良率問題、表面研磨解決橘皮現象，而這些解決方案花費了可觀的成本在人力、工時及物料上。
為了徹底解決上述問題，經過相關文獻閱讀後，提出晶粒細化方法。在相關的文獻提到的晶粒細化熱處理，加入了大量冷作與長時間過時效熱處理，雖能藉此達到9.48μm的晶粒大小，但是各階段製程控制反而增加了額外的成本。
本研究主要目的在找出簡化的晶粒細化製程，同時減低生產成本。研究重點放在冷作加工度、在結晶溫度及時間與均質化熱處理的溫度與時間，而經過簡化製程所細化過的的晶粒大小約10~15μm。
使用TEM觀察鑄錠與粗-細晶管材之後發現，球狀析出物在鑄錠及粗晶管材試片中佈滿基底。球狀析出物在相關文獻中認定為細化的關鍵，因此控制球狀析出物成為簡易晶粒細化製程的關鍵。
人工時效參數的改變也是研究的重點，利用人工時效的研究結果進一步修改晶粒細化的製程。而Al-Mg-Si-Cu管件經過修改過後的製程後，在機械性質有了大幅度的提昇，在熱影響區(HAZ)也無發現溶析裂紋，而抗疲勞性也有了顯著的增加。
本篇論文在數據及部分實驗結果在合作廠商要求下做了刪改。

Abstract
Aluminum alloys have been widely used to produce bicycle frames and components due to their outstanding strength-to-weight ratio. Magnesium and silicon containing 6XXX series alloys are among one of the most commonly used heat treatable aluminum alloys. In order to achieve higher strength, copper is added in Al-Mg-Si-Cu alloys to replace AA6061, which is currently the most commonly used 6XXX series alloy.
However, the metallographically observed coarse grain structure of the aluminum pipes used in producing bicycle frames resulted in high failure percentage during room temperature forming as well as severe orange peel phenomenon on rough surfaces of pipes after forming. Consequently, time-consuming annealing and labor-intensive procedures were added and significantly increased production cost.
In order to solve the aforementioned problems, the cold work and recrystallization induced grain refining was extensively studied and applied. Previous studies indicated that additional large amount of cold work and long-time overaging procedures prior to the recrystallization heat treatment can significantly reduce the grain size to average 9.48μm in diameter. Although the resulting fine microstructure can greatly improve the productivity and quality of the bicycle frames, the additional cost makes this procedure impractical in production.
The major objective of this study was to develop a simplified grain refining procedure and to achieve fine grain structure while maintaining low production cost. A simplified procedure was successfully developed which was focused on the degree of cold work, recrystallization temperature and time, and homogenization temperature and time. As a result, fine grain structure of average grain size of approximately 10 — 15μm in diameter was produced.
Microstructures of aluminum cast and the coarse- and fine-grained pipes were studied using transmission electron microscopy (TEM). Globular precipitates were observed in the matrix of the cast and coarse-grained pipes. It was reported that the existence and distribution of these precipitates were responsible for a successful grain refining procedure. The theory and practical procedure of the modified grain refining procedure developed in this study was also based on the controlling of these precipitates.
Artificial aging procedure was also evaluated and modified in this study. The combination of grain refining procedure and improved aging procedure resulted in a modified procedure. Pipes produced with Al-Mg-Si-Cu alloys and this modified procedure exhibited significant improvement in product quality and yield rate, no cracking in the weld heat-affected zone (HAZ), and increased fatigue resistance of the bicycle frames.
This thesis has been significantly modified and some of the experimental results and data were omitted due to the confidentiality agreement with the sponsored corporation.

目 錄
指導教授推薦書 i
口試委員會審定書 ii
博碩士論文授權書 iii
誌 謝 iv
中文摘要 v
英文摘要 vii
目 錄 ix
表 目 錄 xii
圖 目 錄 xiii
第一章：文獻回顧 1
1.1 前言 1
1.2 鋁合金的用途及分類 4
1.2.1 鋁合金的分類 4
1.2.2 合金元素加入的影響 5
1.2.3 6XXX系列鋁合金 10
1.3 Al-Mg-Si-Cu合金系析出物種類 12
1.3.1 Al-Cu合金 12
1.3.2 Al- Mg-Si合金 13
1.3.3 Al- Cu-Mg合金 15
1.4 實驗相關文獻回顧 17
1.4.1 再回復、再結晶與晶粒成長 17
1.4.2 美國專利細化方法 19
1.4.3 四階段式晶粒細化 20
1.4.4 加入Cu對6xxx鋁合金強度的影響 24
第二章：研究目的 25
第三章：實驗方法及原理 26
3.1 實驗流程圖 26
3.2 實驗設備 27
3.3 實驗材料及TEM試片準備 28
3.4 顯微組織觀察 28
3.5 機械測試 29
3.6 改良式晶粒細化步驟 31
3.7 銲接實體實驗 31
第四章：結果與討論 33
4.1 晶粒細化熱處理 33
4.1.1 再結晶溫度對細化晶粒尺寸及高溫成長模式之影響 33
4.1.2 鑄錠細化結果 37
4.1.3 TEM觀察結果 44
4.2 銲接及銲後熱處理金相觀察 52
4.2.1 熱影響區觀察 53
4.2.2 銲後熱處理金相觀察 54
4.2.3 銲道金相觀察 55
4.3 疲勞測試結果 57
4.3.1 粗晶管件疲勞金相觀察 58
4.3.2 細晶管件疲勞金相觀察 60
4.4 熱處理參數的最佳化 62
4.4.1 金相照片 65
4.4.2 原始數據 66
4.4.3 熱處理最佳化之結果與討論 83
4.5 拉伸試驗結果 96
第五章：結 論 97
參考文獻 99
附錄一：論文英文稿 101

參考文獻
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