臺灣博碩士論文加值系統

鋁合金具有質量輕、機械強度高、導電導熱性良好、易加工及價格低廉等優點，其應用範圍極廣，舉凡傳統工業、航太工業、電子工業等均有其舉足輕重的地位。然而鋁合金容易被磨損、熔點低、表面硬度低及耐磨耗性差等缺點，因此藉由雷射合金化方法改善表面性質。
本文主要研究利用CO2 雷射法在6061 鋁合金表面添加鎳基及鈷基粉末進行合金化，探討其高溫耐磨耗性、顯微組織、成份、硬度及結構變化之影響，並探討合金層熱處理後之變化情形。由實驗結果得知：合金層可分為上表層、次表層、中間層、界面層，產生合金層變化原因取決於冷卻速率及密度比重等等⋯，上表層與界面層因冷卻速率最快，鎳基合金層上表層形成Al3Ni 等軸晶，而次表層主要組織為較大Al3Ni2 樹枝狀晶。中間層為Al-Ni-Cr 非晶質組織。鈷基合金層上表層形成Al9Co2 組織，次表層為Al13Co4 組織，中間層為條狀Al5Co2 組織，在硬度方
面，經過雷射合金化處理後之鎳基及鈷基上表層與界面層受基底效應，因此硬度並無明顯增加，中間層屬於非晶經區域，因此硬度比基材高20 倍。進行250℃耐磨耗測試發現到，基材與鎳基雷射合金化處理後其壽命提昇3 倍。合金層是屬過飽和固溶體狀態，經過熱處理後，上表層α-Al 呈球狀析出，硬度提高為2 倍，熱處理後也可改善鎳金合金層硬度梯度，消除應力集中，不過由於中間層硬度下降，因此對於耐磨耗性質並無明顯提昇。鈷基耐高溫特性較佳，合金層經過熱處理後，不僅上表層硬度增加，中間層較不易重新固溶析出Al9Co2 組織，可保持原有硬度（Hv501038），因此鈷基熱處理試片為本研究中高溫耐磨性最佳之合金層。

Aluminum alloys have been considered to be one of the most versatile useful
materials because of their interesting mechanical properties, such as high strength-weightratio, high electrical conductivity, good thermal conductivity, easy to shape, and relatively inexpensive. However, the low hardness, low melting point of such alloys result in poor friction properties and heat resistance. The Co2 laser alloying is one of the efficient method
to improve the surface wear resistant.This paper is using CO2 laser alloying Ni-based and Co-based powder on the surface of 6061 Al-Mg-Si alloy and than to discuss the wear resistance property on high temperature. In this study we also will discusses the variation of composition, hardness,and the microstructure throughout the alloying layers after heat treatment. As Experimental result；we can find alloying layer can be divided into four layers, such as surface layer,
subsurface layer, middle layer, and interface layer. The main reason to cause the variation of the alloying layer is due to different cooling rate and density. The Ni-based of the surface layer has the Al3Ni oriented microstructure due to rapid fast cooling rate, the subsurface layer has bigger Al3Ni2 dendritic microstructure, and the middle layer has Al-Ni-Cr amorphous microstructure. The Co-based of the surface layer has the Al9Co2 microstructure, the subsurface layer is Al13Co4 microstructure, and the middle layer is strip-like Al5Co2 microstructure. About the hardness test, the surface layer and the interface layer of Ni-based and Co-based after the laser alloying are influenced by effect of substrate.So the hardness is not increasing obviously. The middle layer is belonging to amorphous structure, and its hardness is 20 times than substrate. The life of the Ni-based and Co-based
laser alloying treatment is 3 times as the based material after the wear resistance test under the 250 ℃. After the heat treatment, the α-Al of the alloying surface layer appears the nodulizing precipitation, the hardness is twice than original one. It can also improve the hardness gradient of the Ni-based alloying layers, and decrease the stress concentration.
But the wear resistance property does not increase obviously since decreasing of the hardness in the middle layer. The Co-based alloying has better heat-resistance property.After heat treatment, the hardness of surface layer alloying increases. And the milled layer alloying is hard to solution precipitating Al9Co2 microstructure, it can keep the original hardness（Hv501038）. So the Co-based heat-treatment sample alloying has the best wear
resistance during high temperature (200℃) of this research.

摘要……………………………………………………… Ⅰ
Abstract………………………………………………… Ⅱ
致謝……………………………………………………… Ⅳ
目錄……………………………………………………… Ⅴ
圖目錄…………………………………………………… Ⅶ
表目錄…………………………………………………… Ⅸ第一章緒論…………………………………………………1
1-1 前言……………………………………………………1
1-2 研究動機與目的………………………………………2
第二章理論基礎及文獻回顧………………………………3
2-1 雷射加工的發展………………………………………3
2-2 CO2雷射簡介…………………………………………9
2-3 表面預處理…………………………………………12
2-4 雷射合金化…………………………………………15
2-5 磨耗理論與磨耗機構………………………………23
2-6 雷射合金層的應力狀態、裂縫與變形……………27
第三章實驗方法與步驟…………………………………29
3-1 實驗流程……………………………………………29
3-2 實驗材料……………………………………………30
3-3 實驗設備……………………………………………30
3-4 熱處理………………………………………………31
3-5 雷射合金化…………………………………………31
3-6 性質測試與分析……………………………………33
第四章研究結果與討論…………………………………35
4-1 鎳基合金層顯微組織觀察…………………………35
4-2 鈷基合金層顯微組織觀察…………………………43
4-3 硬度分析……………………………………………50
4-4 熱處理對合金層性質之影響………………………52
4-5 磨耗特性分析………………………………………63
4-6 熱處理對合金層耐磨耗性之影響…………………78
第五章結論………………………………………………80
第六章未來研究發方向與建議…………………………81
第七章參考文獻…………………………………………82

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