The Effect of Pulse Current Frequency to Weldment Structure and Mechanical Properties on 6Al-4V Titanium Alloy
陳家暘、廖芳俊
E-mail: [email protected]
ABSTRACT
According to the highly development of technology, consumers’ demands for products are not function-oriented anymore, but should take the appearance, quality, light and handy, and the endurance into account. Light metal, therefore, becomes the main stream of material in new age. Although, the specific density of titanium (about 4.50 g/cm3) is heavier than the other two
well-known light metals (magnesium and aluminum). However, its outstanding high melting point, high specific strength and rigidity, excellent corrosion resistance, high fatigue strength, high fracture toughness, and biocompatibility, which makes it predominant though. Owing to the increase of demand and promotion of technology, problems of refinement and manufacture skills of Ti in early periods are overcome gradually. It’s believed that the development and application of Ti and Ti alloy are infinite in future. To make a material universal application, extra-work skill plays an important role, joint skill in which especially. For there is few research works on joint of Ti alloy in domestic. In this experiment, we select the most widespread-applied 6Al-4V Titanium alloy by means of gas tungsten arc welding (GTAW/TIG) machine doing the research. Hopes that the influence on weld structure and mechanical properties by changing the frequency of pulse could be understood, then obtain the welding characteristics and the best welding parameter. Based on the results of experiment, it proved that no matter use of the alternating current or the direct current, the frequency of pulse do shown the refined effect on the weldment structure, and the alternating current also showed the stronger effects. This refined result will directly affect the mechanical properties and fracture mode of weldment. Thus, selecting the appropriate current type and pulse frequency will apparently promote the nature of weldment. Hopefully, the results of this investigation will be helpful to the industrials and expand the applications of titanium alloy.
Keywords : Light Metals ; Gas Tungsten Arc Welding ; 6Al-4V Titanium Alloy ; Frequency of Pulse ; Fracture Mode Table of Contents
封面內頁 簽名頁 授權書 iii 中文摘要 v 英文摘要 vii 誌謝 ix 目錄 x 圖目錄 xiv 表目錄 xix 第一章 序論...1 1.1緣起...1 1.2本文目標...4 第二章 文獻回顧...7 2.1簡
介...7 2.2鈦及鈦合金...8 2.3鈦之穩定元素...9 2.3.1 α穩定元 素...9 2.3.2 β穩定元素...10 2.3.3 中性穩定元素...11 2.4鈦合金之分 類...11 2.4.1 α型鈦合金...11 2.4.2 β型鈦合金...12 2.4.3 α＋β型鈦合 金...12 2.4.4近α (near α)型鈦合金...12 2.4.5近β (near β)型鈦合金...12 2.5鈦合金材 料之特性... 13 2.5.1比重低...13 2.5.2比強度/比剛性佳...13 2.5.3優異的耐 蝕性...13 2.5.4傑出的高溫特性...14 2.5.5高疲勞強度...16 2.5.6高破壞韌 性...16 2.5.7彈性模數低...16 2.5.8人體親和性...17 2.5.9鈦合金其它特 性...17 2.6金相顯微組織...18 2.6.1等軸結構...18 2.6.2層狀結
構...18 2.7麻田散體...20 2.7.1板條狀麻田散體...20 2.7.2針狀麻田散 體...20 2.8鈦合金的熔接性...21 2.9接合鈦合金的方法...22 2.10鈦合金銲道 之晶粒細化...24 2.11電弧銲之脈衝電流頻率對銲道微結構的影響...29 2.12銲道之微結構組
織...32 2.13鈦合金銲接前後對硬度的影響...35 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...41 3.4銲接方法介 紹...45 3.5顯微組織的觀察與分析...46 3.6拉伸試驗...47 3.7維氏硬度試 驗...48 3.8計算晶粒尺寸...50 3.9掃瞄式電子顯微鏡(SEM)及X光能量散佈分析儀(EDS).51 第四章 實驗結果之分析與討論...52 4.1 Ti-6Al-4V鈦合金軋延板母材之金相結構組織...52 4.2 Ti-6Al-4V鈦合金板 銲道之巨觀金相結構...53 4.3 Ti-6Al-4V鈦合金板銲道之微觀金相結構...57 4.4 電流輸出模式對鈦合金銲道巨觀結構 尺寸之影響...59 4.5 脈衝電流頻率對銲道機械性質的影響...66 4.5.1脈衝電流之輸出頻率與硬度值的關係...66 4.5.2 脈衝電流頻率對降伏強度之影響...69 4.5.3 脈衝電流頻率對最大拉伸強度之影響...69 4.5.4 脈衝電流頻率對伸長 率之影響...70 4.5.5 脈衝電流頻率對韌性值之影響...70 4.6銲道拉伸試片破斷面的分析...75 4.6.1 母材之拉伸破斷面分析...75 4.6.2 不同脈衝頻率之銲道拉伸試片破斷面分析...76 第五章 結
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