鋁合金6061-T6鎢極惰性氣體保護銲與真空硬銲接頭之疲勞壽命評估研究;Fatigue Assessment of 6061-T6 Aluminium Alloy Joints Processed by Tungsten Inert Gas Welding and Vacuum Brazing

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題名:	鋁合金6061-T6鎢極惰性氣體保護銲與真空硬銲接頭之疲勞壽命評估研究;Fatigue Assessment of 6061-T6 Aluminium Alloy Joints Processed by Tungsten Inert Gas Welding and Vacuum Brazing
作者:	林暉;Lin,Huei
貢獻者:	機械工程學系
關鍵詞:	真空硬銲;鎢極惰性氣體保護銲;鋁合金;疲勞壽命;平均應力;尺寸效應;Vacuum brazing;tungsten inert gas welding;aluminum alloy;fatigue;mean stress effect;size effect
日期:	2016-06-21
上傳時間:	2016-10-13 14:49:15 (UTC+8)
出版者:	國立中央大學
摘要:	本研究以熱處理型6061-T6鋁合金為實驗材料，選擇對接與T型接頭，進行鎢極惰性氣體保護銲與真空硬銲，對於鋁合金銲接結構件在等負荷振幅及變動負荷振幅下之疲勞性質及疲勞壽命分析模式進行深入研究。為探討原始銲接結構之疲勞分析方法，將檢視各設計規範之適用性，並建立鋁合金銲接結構在不同受力情況下之最佳疲勞壽命分析模式。研究結果顯示鎢極惰性氣體保護銲最低硬度值位於熱影響區，而真空硬銲並無明顯熱影響區，因真空硬銲是使用熱輻射方式且加熱均勻。在對接接頭拉伸性質方面，當試片厚度增加，鎢極惰性氣體保護銲試片拉伸強度減少，但是，真空硬銲試片拉伸強度增加。因真空硬銲屬於擴散銲接，當硬銲接觸面積愈大，可有效提升拉伸強度。在疲勞性質方面，不論是對接接頭或是T型接頭，鎢極惰性氣體保護銲試片疲勞強度皆高於IIW、BS 8118及Eurocode 9等規範設計曲線。在真空硬銲試片，T型接頭之疲勞強度高於IIW FAT 28、BS 8118 class 29及Eurocode 9 category 31等規範設計曲線，但關於對接接頭，其疲勞性質不適用於IIW FAT 45規範。在平均應力修正方面，當平均應力為拉伸時，鋁合金6061-T6厚度4 mm之疲勞壽命預測，不論是鎢極惰性氣體保護銲或真空硬銲，皆適用Goodman平均應力修正。但對於T型接頭在支架歷程(平均應力為輕微壓縮)之疲勞壽命預測，鎢極惰性氣體保護銲適用於S-N方法，真空硬銲適用於Goodman平均應力修正。在厚度修正方面，不論是對接接頭或是T型接頭，鎢極惰性氣體保護銲適用於IIW規範厚度修正公式，但對於真空硬銲之對接接頭，本研究提出一個新的厚度修正公式(利用抗拉強度比值進行厚度修正)，其厚度修正結果優於IIW規範。對於T型接頭，在高壽命區間，則須做厚度修正。 ;Tungsten inert gas welding and vacuum brazing butt joints and T-joints of Al–Mg–Si alloy 6061 in the artificially aged condition T6 were studied. Microhardness, tensile, constant amplitude and variable amplitude fatigue loading tests were performed. The experimental S-N curves were compared with the fatigue design curves recommended by the International Institute of Welding, British Standard, and Eurocode 9. Two mean stress correction methods, Goodman and Gerber, were evaluated. For the tungsten inert gas welding joints, the area with the lowest microhardness was the HAZ. For the vacuum brazing specimen, no clear HAZ was observed. Because the weldment was heated to a uniform temperature in a vacuum, so local overheating did not occur. In terms of the tensile properties of butt joints, the tensile strength of the vacuum brazing specimen increased with specimen thickness, whereas that of the tungsten inert gas welding welding specimen decreased. Tungsten inert gas welding butt joints and T-joints of AA 6061-T6 achieved higher fatigue strength as compared to the fatigue design curves of IIW, BS 8118, and Eurocode 9. In the lower life region (N = 104 ~ 105), it was found that the fatigue strength of vacuum brazing butt joints was lower than that of IIW FAT 45, but still higher than those of the BS 8118 class 42 and Eurocode 9 category 56-7. When tungsten inert gas welding or vacuum brazing joints of aluminum 6061-T6 was subjected to a variable amplitude loading with tensile mean stress, Goodman method was suitable to modify the mean stress effect. For T-joints, the fatigue life of the tungsten inert gas welding specimens given the bracket history can be predicted using the S-N method. The fatigue life of the vacuum brazing specimens under the bracket history can be predicted using the Goodman mean stress correction method. In terms of the size effect on the fatigue life, the thickness correction method recommended by the IIW was applicable to the tungsten inert gas welding joints of aluminum 6061-T6. This article proposed an innovational thickness correction method based on the ratio of the ultimate tensile strengths of specimens with different thickness. For butt joints of vacuum brazing, the tensile strength–based thickness correction method was better than the thickness correction methods recommended by the International Institute of Welding. For T-joints, vacuum brazing is required to carry out thickness correction in the higher life region.
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