The plastic deformation behaviour and microstructure characteristic of 7075 Al alloy loaded with low and high strain rate under different manufacturing processes.

• Main Authors: Wu, Chin-Jyi, 吳清吉
• Other Authors: Woei-Shyan Lee
• Format: Others
• Language: zh-TW
• Published: 1998
• Online Access: http://ndltd.ncl.edu.tw/handle/59819970592779187226

碩士 === 國立成功大學 === 機械工程學系 === 86 === The purpose of this study is to investigate the plastic deformation behaviour of 7075 Al alloy subjected to different manufacturing processes. The"dynamic" ranges (1300s^-1 ~4100s^-1 ) and at temperature ranging from 25℃ to 300℃ by using constant-strain-rate isothermal tester and Split-Hopkinson bar tester. After mechanical test, the microscopic techniques were used to examinethe variation of microstructure in terms of testing conditions. With the macroscopic and microscopic results, a constitutive equation is used to describethe plastic deformation behaviour of the material under high strain rate and high temperature conditions. The experimental results indicated that temperature and strain rate effect strongly the mechanical characteristics of 7075 Al alloy, and that different manufacturing processes also play an important role to mechanical response of this material. Microstructural observations find that the strength of tested material varies markedly with the density of precipitates and that the features and arrangement of precipitates depend strongly on strain rate, temperature and different manufacturing processes. The failure analysis shows that the fracture is dominated by a shear failure mode and that the shear bands are theprecursor to crack formation and fracture. The characteristics of shear bands vary completely with testing conditions and matrix hardness. Finally, by comparing the results of mechanical testing with those of Kobayashi & Dodd equation, the constitutive equation predicts an acceptable flow stress value with reasonable extent of error.