The Effect of Pulse Current to the Micro Structure and Mechanical Properties on AZ80A Magnesium Alloy Welds 林家慶、廖芳俊

The Effect of Pulse Current to the Micro Structure and Mechanical Properties on AZ80A Magnesium Alloy Welds

林家慶、廖芳俊

E-mail: [email protected]

ABSTRACT

According to the high development of technology, consumer demands for product are changed from function-oriented to fine quality and light-weight behavior. Also the "Green concept" is highly emphasized in the worldwide. The vehicle industries are selecting light weight materials to fabricate the vehicle to reduce the exhaust gases emission and increase the fuel efficiency. As we know,

magnesium alloy exist many excellent characteristics; ex: low specific density, high specific strength and rigidity, good thermal conductivity, high damping capacity, and high electromagnetic interference, etc. Nevertheless, the HCP crystal structure causes the inferior results of formability and ductility. Therefore, not only improve the quality and properties of material but promote the manufacture processing techniques are important. One of the important techniques is the welding technology. In here, we select the most popular welding machine in manufacture industry, gas tungsten arc welding (GTAW), doing this welding research. Hopes that the influence on weld structure and mechanical properties by changing the frequency of alternating current (AC) and pulsing current could be understood, then obtain the welding characteristics and the best welding parameters of AZ80A magnesium alloy. Based on the experiment results shown that, the influence of AC frequency do not show clear affect to the weld property. However, by changing the frequency of pulsing current did obviously reveal the influence to the weld. With increasing the pulsing frequency, the grain refinement effect is very clearly, which will increase the mechanical properties (such as tensile strength, elongation, and toughness) gradually. Especially, at 9 Hz weld can obtain the finest grain size. Hopefully, the result of this study not only can accumulate the knowledge of magnesium welding, but also helps the traditional metal working industries to promote their welding skills and expand the applications of magnesium alloy.

Keywords : AZ80A Magnesium Alloy, Pulsing Current, Grain Refinement, Mechanical Properties Table of Contents

封面內頁 簽名頁 授權書……… iii 中文摘要………

……… v 英文摘要……… vii 致 謝……… ix 目錄………

……… x 圖目錄……… xiii 表目錄………

……… xvi 第一章 序論………

… 1 1.1 前言……… 1 1.2 目前鎂合金之應用………

……… 3 1.3 本文目標……… 7 第二章 文獻回顧………

……… 9 2.1 鎂合金的簡介……… 9 2.2 鎂 合金之命名方法……… 11 2.3 鎂合金材料之特性………

……… 13 2.3.1 比重低……… 13 2.3.2 比強度/比剛性佳 ………

……… 13 2.3.3 可回收性佳……… 13 2.3.4 吸震性佳…………

……… 14 2.3.5 熱傳散熱性佳……… 14 2.3.6 電 磁波遮蔽性佳……… 14 2.4 鎂合金之銲接性研究………

……… 17 2.4.1 鎂合金的銲接特性……… 17 2.4.2 可銲性的意義………

……… 18 2.4.3 鎂合金的可銲性……… 19 2.5 鎂合金的銲接方式……

……… 22 2.5.1 電弧銲接……… 22 2.5.2 雷 射束銲接……… 26 2.5.3 電子束銲接………

…… 27 2.6 熔融銲接的凝固特徵與型態……… 30 2.7 電弧銲之脈衝電流對銲道微結構的影響

……… 32 第三章 實驗方法……… 34 3.1 實驗材料……

……… 34 3.2 實驗規劃………

36 3.3 實驗步驟……… 38 3.4 銲接方式………

……… 40 3.5 顯微組織的觀察……… 42 3.6 拉伸試驗………

……… 43 3.7 微硬度試驗……… 44 3.8 晶

粒尺寸的量測計算……… 45 3.9 掃描式電子顯微鏡(SEM) ………

……… 46 第四章 實驗結果分析與討論……… 47 4.1 改變交流電頻率之AZ80A 鎂 合金銲道性質……… 47 4.1.1 改變交流電頻率對銲道晶粒尺寸之影響……… 47 4.1.2 改變交 流電頻率對銲道機械性質之影響……… 47 4.1.2.1 交流電頻率對銲道微硬度值之影響……… 51 4.1.2.2 交流電頻率對最大拉伸強度之影響……… 52 4.1.2.3 交流電頻率對伸長率之影響………

……… 52 4.1.2.4 交流電頻率對韌性值之影響……… 52 4.1.3 交流電頻率晶粒尺寸與降伏強度的關係…

……… 54 4.2 改變脈衝電流頻率之銲道性質……… 55 4.2.1 改變脈衝頻率對銲道晶 粒尺寸之影響……… 55 4.2.2 改變脈衝頻率對銲道機械性質之影響……… 55 4.2.2.1 脈衝頻 率對銲道微硬度值之影響……… 55 4.2.2.2 脈衝頻率對最大拉伸強度之影響……… 58 4.2.2.3 脈衝頻率對伸長率之影響……… 59 4.2.2.4 脈衝頻率對韌性值之影響………

……… 59 4.2.3 脈衝頻率晶粒尺寸與降伏強度的關係……… 62 4.3 銲道拉伸試片破斷面的分析………

……… 63 4.3.1 母材之拉伸破斷面分析……… 63 4.3.2 不同脈衝頻率銲道 之拉伸破斷面分析……… 64 第五章 結論……… 71 參 考文獻 ……… 73

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