Materials Reports  2019, Vol. 33 Issue (Z2): 394-397 |
| METALS AND METAL MATRIX COMPOSITES |
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| Effect of Non-isothermal Retrogression and Re-ageing Treatments on theMicrostructure and Mechanical Properties of 7050 Alloy |
| WU Yiping1, HE Zhenyi1, ZHOU Zhigang1, XIONG Hanqing1, JIA Yuzhen2, LI Chengbo3, LI Guofeng1
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1 Department of Mechanical and Electrical Engineering, Changsha University, Changsha 410022;
2 Bichamp Cutting Technology (Hunan) Co., Ltd., Changsha 410200;
3 School of Materials Science and Engineering, Central South University, Changsha 410200 |
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Abstract The effects of “non-isothermal retrogression and re-ageing” treatments on the microstructure and mechanical properties of a 7050 alloy were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), hardness test and tensile test. During the non-isothermal retrogression process with a heating rate of 5 ℃/min, five terminal temperatures of 160 ℃, 190 ℃, 220 ℃, 260 ℃ and 300 ℃ were selected. The results show that after the non-isothermal retrogression and re-ageing treatment of 120 ℃/24 h+RT5 ℃/min190 ℃+120 ℃/24 h, the alloy presents the best mechanical properties with the ultimate tensile strength of 588 MPa, yield tensile strength of 558 MPa and ductility of 23%, respectively; the hardness is 199HV. In the pre-aged alloy, the equilbrium η phases along the grain boundaries are discontinuously located with an average size of 49—70 nm, and the η′ phases in the grains have an average size of 5—6 nm. During the retrogression with the continuous temperature increasing to 190 ℃, the pre-precipitated phases are partly dissolved and the sizes are smaller: the grain boundary η phases have an average size of 5—10 nm, and the phases within the grains have an average size of 3—6 nm. The retrogression alloy has multiple and parallel grain boundaries with unobvious PFZ. The re-aged alloy has the biggest phases in an average size of 91—108 nm along grain boundaries and diffuse phases inside grains in an average size of 4—10 nm, and its PFZ becomes clear with a width of 41 nm.
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Published: 25 November 2019
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| Fund:This work was financially supported by the Changsha Science and Technology Project (K1705055) and the Key Youth Project for Scientific Research from Education department of Hunan province (17A019). |
About author:: Yiping Wu is a lecturer in Changsha University. She received her B.E., M.E. and Ph.D. degree in materials science and engineering from the Central South University (CSU) in Sep. 2004—Dec. 2015. She has published more than 10 journal papers as the first author, applied 1 national invention patent. Her research inte-rests focus on the light metals with national research priority, and the fundamental theory & application about the advanced processing and microstructure & property control.
Guofeng Li is a professor in Changsha University. He obtained his B.E. degree from Central South University (CSU) in 1983, and then served in Central South University, Changsha ZHONG-YI electrical device company and Changsha University. His team’s research interests are aluminum plastic deformation and its strengthening and toughening mechanisms. He has anticipated 2 national key programs, hosted 4 province programs and 3 city programs. He has published more than 30 journal papers, and applied many national invention patents and 3 of them were authorized. He has also developed more than 20 new products. He was autho-rized 1 province award for scientific and technological advancement and 3 teaching achievement awards. |
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