純鈦與Ti-6Al-4V合金同質摩擦攪拌銲接之機械性質與抗腐蝕特性研究

Abstract

本研究使用摩擦攪拌銲接(FSW)技術對Gr. 2 CP-Ti及Ti-6Al-4V進行同質對接，使用碳化鎢圓球形凸銷攪拌棒作為銲接工具，銲接過程攪拌棒傾斜角分別使用3°及1°，且下壓深度分別為1.9 mm及1.8 mm，探討不同主軸轉速、進給速度對於銲接件機械性質及抗腐蝕能力的影響，利用金相組織觀察、抗拉試驗、微硬度試驗等作為機械性質分析。在抗腐蝕分析中使用3.5 wt %氯化鈉水溶液模擬海水中使用狀態進行各參數銲道及熱影響區抗腐蝕性質比較，另外將摩擦攪拌銲接實驗數據與惰氣鎢極電弧銲(GTAW)進行銲後性質比較。實驗結果在使用圓球形凸銷攪拌棒時，可以增加材料的塑性流動方向，且在成功的銲接參數下，拉伸斷裂位置都出現在母材，在CP-Ti摩擦攪拌銲接的主軸轉速600 rpm、進給速度80 mm/min有最佳銲接性質，抗拉強度為395 MPa，為母材的 94.8 %，而Ti-6Al-4V最佳銲接性質在主軸轉速900 rpm、進給速度40 mm/min時，抗拉強度為1059 MPa，為母材的99.3 %。從純鈦的銲接攪拌區可觀察到明顯的晶粒細化現象，且微硬度直達180 HV，Ti-6Al-4V合金的攪拌區則為針狀的費德曼組織，且攪拌區也有明顯的硬度提升，相較於GTAW，FSW在純鈦接合中有較佳的延伸率，而在Ti-6Al-4V接合中FSW有較優異的機械性質表現。在CP-Ti、Ti-6Al-4V銲後抗腐蝕性研究中，兩種接合法之銲道受組織改變影響，抗腐蝕性均低於母材， FSW的攪拌區及熱影響區相較於GTAW銲道，FSW在抗腐蝕能力中有明顯提升，其中Ti-6Al-4V經FSW在主軸轉速1000 rpm、進給速度40 mm/min 的銲道表面及攪拌區底部未相變態之晶粒細化組織，使抗腐蝕性大幅提升，且優於母材。

This study employed friction stir welding (FSW) technique to perform similar joining of Gr. 2 commercially pure titanium and Ti-6Al-4V alloy. Tungsten carbide spherical tool pin was used as the welding tool. The tilt angles of the tool pin during the welding process were set at three degrees and one degree, with plunging depths of 1.9 mm and 1.8 mm, respectively. The effects of different spindle speeds and feed rates on the mechanical properties and corrosion resistance of the welds were investigated. Analysis of mechanical properties included metallographic observation, tensile testing, and microhardness testing. Corrosion resistance analysis involves comparing the weld and heat-affected zone under various parameters using a 3.5 wt% sodium chloride solution to simulate seawater corrosion. Additionally, the FSW experimental data was compared with the post-weld properties of gas tungsten arc welding (GTAW).The experimental results showed that using a spherical tool pin could enhance the material's plastic flow direction. Under successful welding parameters, the tensile fractures occurred in the base material. For pure titanium friction stir welding, the best welding properties were achieved at a spindle speed of 600 rpm and a feed rate of 80 mm/min, with a tensile strength of 395 MPa, which was 94.8% of the base material. As for Ti-6Al-4V, the optimum welding properties were achieved at a spindle speed of 900 rpm and a feed rate of 40 mm/min, with a tensile strength of 1059 MPa, whichwas 99.3% of the base material. Significant grain refinement was observed in the friction stir zone of pure titanium, with a microhardness reaching 180 HV. The stir zone of Ti-6Al-4V exhibited needle-like Widmanstatten microstructure, along with a noticeable increase in hardness. Compared to GTAW, FSW demonstrated superior tensile elongation in pure titanium joints, while FSW shows better mechanical properties in Ti-6Al-4V joints. In terms of corrosion resistance, the stir zone and heat-affected zone of FSW exhibited better performance than GTAW welds, indicating improved corrosion resistance in FSW. In the study of post-weld corrosion resistance for CP-Ti and Ti-6Al-4V, the welds formed by two different joining methods were found to have been affected by microstructural changes, resulting in diminished corrosion resistance compared to the base materials. Notably, the friction stir welding (FSW) technique exhibited a pronounced enhancement in corrosion resistance when compared to gas tungsten arc welding (GTAW). Specifically, Ti-6Al-4V that underwent FSW at a spindle speed of 1000 rpm and a feed rate of 40 mm/min showed a substantial increase in corrosion resistance. This improvement was attributed to a refined grain structure on the surface of the weld and at the base of the stir zone, without undergoing phase transformation. The resulting corrosion resistance of these FSW-treated welds surpassed that of the base material. These findings underscored the potential of FSW to significantly enhance corrosion resistance, particularly under specific welding conditions, offering promising implications for improving the longevity of welded joints.