臺灣博碩士論文加值系統

本研究是以連續式CO2雷射對AZ61與AZ80鎂合金擠製板材進行銲接，探討熱處理前後對銲接的差異性。並研究銲接參數對機械性質、微觀組織、化學成份、銲接缺陷等的影響，進而改善擠製板材之可銲性。
母材及銲道以掃描式電子顯微鏡(Scanning electron microscope , SEM)觀察及能量分散光譜儀(Energy dispersive X-ray spectroscopy , EDS)分析，發現熱處理後會有更多的鋁與鋅在晶界上偏析。鋁含量高的合金母材在相同入熱量下有較寬的銲道。熔融線附近有較多的鋁偏析，銲道內樹枝狀結構鋁含量也較高。
由實驗結果顯示入熱量越大銲道截面積越大，且熔融線有滲入母材的現象。低入熱量銲接可提升抗拉強度，因為銲道結晶組織緻密及較小的熱影響區，且不易產生不穩定的電漿氣而造成銲道氣孔缺陷。但走速過快會造成較大的過冷區，使熔融線的凝固速率快於部分熔融區，在部份熔融區產生液化裂縫，反而降低抗拉強度。將液化裂縫周圍組織做EDS分析發現鋁偏析的現象。

Investigation of CO2 laser welding has been done to AZ61 and AZ80 magnesium alloy extrusion sheet. Material without heat treatment has been compared with material which heat treated prior to welding. The aim of this research was to study the effect of different heat input of CO2 laser welding on mechanical properties, microstructure, chemical composition and welding defects of the magnesium alloy extrusion sheet in order to improve the weldability.
Base metal and weld metal were observed with the scanning electron microscope. Energy dispersive X-ray spectroscopy analysis reveals that the heat treatment materials have more Al and Zn element segregation in grain boundary. When the alloy with higher aluminum content has wider weld zone in the same heat input relatively. Near the fusion line becomes more Al element segregation and in the weld region the dendritic compounds relatively contain high Al.
Experimental results showed that the width of weld cross section was increased with the increment of heat input, and the fusion line has permeated into base metal. The low heat input would increase tensile strength, because the fusion zone has finer crystal microstructure and the heat affected zone width was reduced. It is difficult to produced unstable plasma which leads to weld porosity. But high welding speed brought the big supercooling area ,fusion line solidify in advance prior to partially melted zone (PMZ), cause liquation cracking in the PMZ which lead to loss of tensile strength. Segregation phenomenon of some Al element in liquation cracking has been taken to analyze by EDS.

目 錄
摘要 I
ABSTRACT II
誌 謝 III
目 錄 IV
表 目 錄 VII
圖 目 錄 VIII
第一章 前言 1
1.1 研究動機 1
1.2 研究目的 2
第二章 文獻回顧 3
2.1 加工用之雷射 3
2.1.1 二氧化碳雷射 5
2.1.2 雷射銲接機制與特性 7
2.1.3 雷射銲接製程變數 9
2.2 鎂合金簡介 13
2.2.1 鎂合金的特性 13
2.2.2 鎂合金命名法 14
2.2.3合金元素添加對鎂合金之影響 14
2.3 鎂合金擠製板材之特性 18
2.4 鎂合金之熱處理性質 19
2.5 鎂合金之銲接性質 21
2.5.1 鎂合金之銲接結晶組織 23
2.6 鎂合金之銲接缺陷 25
2.6.1 銲道氣孔(Weld Porosity) 25
2.6.2 銲道裂縫(Weld Cracking) 28
2.6.2.1 凝固熱裂(Solidification Cracking) 28
2.6.2.2 液化熱裂(Liquation Cracking) 30
第三章 實驗方法 33
3.1 實驗流程 33
3.2 實驗設備 34
3.3 實驗材料 36
3.4 實驗參數設計 37
3.5 拉伸試驗 38
3.6 金相觀察顯微組織觀察 40
3.7 EDS成分分析 40
3.8 破斷面分析 40
第四章 結果與討論 41
4.1 拉伸試驗 41
4.2 銲接試片金相分析 49
4.3 銲接缺陷分析 62
4.3.1 銲接氣孔缺陷 62
4.3.2 液化裂縫缺陷 67
4.4 SEM觀察及EDS分析 72
4.5 拉伸破斷面分析 80
第五章 結論 87
第六章 參考文獻 89

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