The Study of Mechanical Properties after Thermal Cycling in 7050 T6 Aluminum Alloy

• Main Authors: Jui-Hsien Lee, 李瑞賢
• Other Authors: Kuen-Ming Shu
• Format: Others
• Language: zh-TW
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/ym975w

碩士 === 國立虎尾科技大學 === 機械與電腦輔助工程系碩士班在職專班 === 104 === 　　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.