AA7075鋁合金與Ti-6Al-4V合金摩擦攪拌銲接微觀組織與機械性質研究

Research on Microstructure and Mechanical Properties of Friction Stir Welding of AA7075 Aluminum Alloy and Ti-6Al-4V Alloy

鄭元愷(Cheng Yuan-Kai)

指導教授 ： 程金保

國立臺灣師範大學/科技與工程學院/機電工程學系/碩士(2021年)

https://doi.org/10.6345/NTNU202101705

摘要

本研究選用Ti-6Al-4V合金與AA7075合金，以FSW進行AA7075/ AA7075、AA7075/ Ti-6Al-4V 同質與異質的接合。找出合適的銲接參數後，對同質銲件施以T6銲後熱處理，比較T6銲後熱處理對機械性質之影響，並對各組銲接條件進行機械性質、微觀組織與電化學抗腐蝕性探討。
在AA7075/ AA7075同質FSW研究結果顯示，以圓錐攪拌銷可以成功接合的條件需以較高熱量輸入，接合後攪拌區因動態再結晶而產生晶粒細化，而熱影響區則有晶粒粗大化現象，導致銲道附近之硬度下降。同質銲件施以T6銲後熱處理後銲道整體硬度均提升到原有母材硬度，銲件最大抗拉強度達到489.8 MPa，為鋁合金母材強度之82%，但延伸率則至7.3%。而AA7075/ Ti-6Al-4V異質FSW研究結果顯示，若以較高熱量輸入之銲接參數進行接合，將因兩合金之熱膨脹程度不一在銲道產生裂縫。根據EPMA觀察結果顯示，在兩種合金界面出現金屬間化合物(IMC)，IMC的厚度與形成的形式隨轉速而改變，無論轉速高低皆在界面處量測到鈦元素擴散至鋁合金，擴散範圍與轉速高低成正比。銲接參數為540 rpm – 60 mm/min時有最高抗拉強度248.44 MPa，為鋁合金母材強度之41%。電化學腐蝕試驗結果顯示，AA7075因FSW後銲道產生晶粒細化效果，導致單位面積下有更多連續晶界存在，引起更多晶界的腐蝕行為，因此抗腐蝕性較母材差。Ti-6Al-4V則因FSW攪拌棒肩部接觸之銲道表面晶粒尺寸較母材區域小，有更多鈍化膜成核點的形成，因此其抗腐蝕性優於其母材。

關鍵字

鋁合金 ； 鈦合金 ； 摩擦攪拌銲接 ； 異質接合

並列摘要

In this research, friction stir welding (FSW) are conducted using Ti-6Al-4V alloy and AA7075 alloy, joints AA7075 to AA7075 and dissimilar joints AA7075 to Ti-6Al-4V. Apply T6 post-weld heat treatment to similar weldments, and compare the effect of T6 post-weld heat treatment on mechanical properties. Discuss that the mechanical properties and microstructure are affected by welding parameterrs.
The results of the same joints show that welding conditions with higher heat input are required. After joining, the stirring zone produces grain refinement due to dynamic recrystallization, while the heat-affected zone has grain coarsening, which causes the hardness near the weld bead to decrease. The maximum tensile strength of the weld bead after PWHT reaches 489.8 MPa, which is 82% of the strength of the aluminum alloy base metal, but the best elongation is only 7.3%.
The results of the dissimilar joints show that if welding parameters with higher heat input are used for joining, cracks will occur in the weld bead due to the difference in the degree of thermal expansion of the two alloys. According to the EPMA results, the intermetallic compound (IMC) appears at the interface of the two alloys and the titanium element diffuses into the aluminum alloy. The thickness and form of the IMC and the diffusion range of the titanium element change with the rotation speed. When the welding parameters are 540 rpm-60 mm/min, the highest tensile strength is 248.44 MPa, which is 41% of the strength of the aluminum alloy base material.
Electrochemical corrosion test results show that FSW weld bead of AA7075 has a grain refinement effect, resulting in more continuous grain boundaries, causing more grain boundary corrosion behavior. FSW weld bead of Ti-6Al-4V has more passivation film nucleation points on the grain boundary due to grain refinement. So it has better corrosion resistance.

並列關鍵字

aluminum alloy ； titanium alloy ； friction stir welding ； dissimilar joint

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