7075鋁合金同質與純鈦異質摩擦攪拌銲接之接合特性與熱處理效應研究

Abstract

本研究分別選用AA7075-T6、AA7075-O、Gr.2 Ti，三種材料，對AA7075-O進行熱處理、FSW(800 rpm搭配50 mm/min)、銲後熱處理；對AA7075-T6 進行單雙面FSW(600 rpm搭配60 mm/min) 、銲後熱處理；對AA7075-T6與Gr.2 Ti 進行FSW(600 rpm搭配40 mm/min)，對其上三種不同組合所達成的銲接條件進行機械性質與微觀組織的分析與探討。在AA7075-T6材的研究顯示，雙面銲接由於多一道銲接過程，更多的熱量提供使其在機械性質表現上較單面銲接降低，但在銲後熱處理後，其拉伸性質則較單面銲接增加，二者在銲道皆面臨AGG異常晶粒生長的狀況，經熱處理後產生脆性斷裂的問題。在AA7075-O材的研究結果顯示，熱處理時時效溫度越高會導致材料特性抵達峰值時間越少，但其峰值表現也會越低。AA7075-O在銲接後，於其銲道有晶粒細化的表現，因此該區域硬度獲得提升，但在愈遠離銲道則愈發降低，直至母材強度。經銲後熱處理後，若要成功獲得優良的機械性質，必須避免銲道裂縫與AGG的產生，經銲後熱處理之試片與母材熱處理後之機械性質趨勢一致，皆能達成約母材熱處理的80%強度，並且在與T6材FSW的銲接性質比較中，更為提升。而其中AA7075-O在進行銲後與固溶淬火後的拉伸試驗中，可以發現有DSA的產生，能為其增加強度。在AA7075-T6與Gr.2 Ti 異質銲接的研究結果顯示，在600 rpm搭配40 mm/min可以達到無缺陷接合，從EPMA的觀察中可以發現，僅0.1 mm的偏置距離已讓鈦和鋁合金在攪拌區形成化合物及鈦碎屑的攪拌，而IMC層由於其硬脆的特性，導致拉伸試驗皆斷裂於該處。This research explored three different materials: AA7075-T6, AA7075-O, and Gr.2 Ti, using various welding and post-welding heat treatment processes. For AA7075-O, the processes included heat treatment, Friction Stir Welding (FSW), and post-weld heat treatment. For AA7075-T6, single and double-sided FSW and post-weld heat treatment were performed. Lastly, FSW was conducted between AA7075-T6 and Gr.2 Ti, and the mechanical properties and microstructure of these three combinations were analyzed and discussed.In the investigation of AA7075-T6, double-sided welding showed slightly inferior mechanical properties compared to single-sided welding due to the additional welding process and higher heat input. However, post-weld heat treatment improved its tensile properties, showing slightly higher performance than single-sided welding. Both welds faced the issue of abnormal grain growth (AGG) in the weld zone, which, if not avoided, could lead to brittle fracture after heat treatment.For AA7075-O, the research showed that higher aging temperatures during heat treatment caused the material's characteristics to peak earlier but at lower levels, and vice versa. The welded zone exhibited grain refinement, resulting in increased hardness in that area, while the hardness decreased as one moved further away from the weld zone, eventually reaching the base material's strength. After post-weld heat treatment, obtaining excellent mechanical properties required avoiding weld cracking and AGG. The mechanical properties of the samples treated with post-weld heat treatment aligned with the trend of the base material after heat treatment, achieving approximately 80% of the base material's strength. Moreover, the properties compared to FSW welding with AA7075-T6 improved. Regarding the dissimilar welding of AA7075-T6 and Gr.2 Ti, EPMA observations revealed that even a small offset distance of 0.1 mm resulted in the formation of compounds and titanium debris in the stirring zone between titanium and aluminum alloys. The presence of an IMC (Intermetallic Compound) layer led to fracture in tensile tests due to its brittle nature.