- 學位論文
7050 T6鋁合金經熱循環之機械性質研究
The Study of Mechanical Properties after Thermal Cycling in 7050 T6 Aluminum Alloy
摘要
本研究主要探究T6熱處理後之7050鋁合金經60℃、85℃及室溫(25℃)熱循環過程其機械性質的表現以及微結構觀察。主要之實驗內容與方法分別為：(a)在機械性質測試方面，測試方法選擇硬度實驗(洛氏硬度，HRB)導電度(IACS%)及拉伸試驗(tensile test)；(b)顯微結構分析方面，以光學顯微鏡(OM)觀察AA 7050 T6在熱循環過程中微結構的變化。 本論文研究結果顯示AA7050 T6鋁合金經25℃及60℃熱循環過程後，硬度值隨熱循環有不規則起伏變動的現象，但皆不顯著。而AA 7050 T6樣品經85℃熱循環之硬度實驗，結果顯示硬度值也有起伏變動的情形產生，於25~55次循環過程有整體的上升趨勢，於60次循環後，硬度值並未隨著熱循環數發生顯著的改變，亦無整體的上升或下降趨勢，但變動的幅度較60℃及25℃熱循環實驗結果大。導電度(IACS%)據此實驗結果觀察到，導電度與硬度呈反比現象。 拉伸結果顯示各條件之伸長率相近，因此各斷面型態相似，皆為脆性斷裂，伸長率愈低之斷口，二次裂縫愈加明顯。金相微觀組織觀察，晶粒尺寸愈小，降伏強度及硬度值愈高。
並列摘要
This study investigated the mechanical properties and microstructures of 7050-T6 aluminum alloys (AA7050-T6) after heat cycling at 60°C, 85°C, and room temperature (25°C). The experimental methods were as follows: (a) For the mechanical properties, the Rockwell B scale was used to identify the hardness, the International Annealed Copper Standard was used to obtain the electrical conductivity, and a tensile test was conducted to measure the elongation; and (b) An optical microscope was used to observe changes in microstructures of the AA7050-T6 during thermal cycling. The results revealed that the hardness fluctuated irregularly yet no significantly after thermal cycling at 25°C and 60°C. The hardness also fluctuated after heat cycling at 85°C. During the 25th–55th cycles at 85°C, the overall hardness increased gradually. However, the hardness did not vary substantially after the 60th heat cycle, although the magnitude of change exceeded that observed during heat cycling at 65°C and 25°C.The experimental results also demonstrated that the conductivity was inversely proportional to the hardness. The tensile test results revealed similar elongation rates among the samples subjected to thermal cycling at the three temperatures. All fractures were therefore similar in type and were brittle fractures. Shorter fractures exhibited increasingly more substantial secondary cracks. Metallographic observation of the AA7050-T6 microstructure revealed that the smaller the crystal grains were, the greater the yield strength and hardness were.