| Title |
Effect of Dissolution of η′ Precipitates on Mechanical Properties of A7075-T6 Alloy |
| Authors |
김영위(Young-we Kim); 조용희(Yong-hee Jo); 이윤수(Yun-soo Lee); 김형욱(Hyoung-wook Kim); 이제인(Je-in Lee) |
| DOI |
https://doi.org/10.3365/KJMM.2022.60.1.83 |
| ISSN |
1738-8228(ISSN), 2288-8241(eISSN) |
| Keywords |
Al-Zn-Mg-Cu; 7075; dissolution; precipitation; mechanical properties |
| Abstract |
The effects of dissolution of the η′ phase by solution treatment on the mechanical properties of A7075-T6 alloy were investigated. Immediately after solution treatment of the T6 sheet at 450 ℃ or higher, elongation significantly increased and dissolution of the η′ phase occurred. η′ is the main hardening phase. After natural-aging, GPI, which is coherent with the aluminum matrix, was formed and strength increased. When bake hardening after natural-aging was performed, the yield strength slightly increased due to partial dissolution of the GPI and re-precipitation of the η′ phase. In contrast, after solution treatment at 400 ℃, there was less elongation increase due to the precipitation of the coarse η phase at grain boundaries and low dissolution of the η′ phase. In addition, when bake hardening after natural-aging was performed, the yield strength decreased due to insufficient GPI, which is the nucleation site of the η′ phase. To promote re-precipitation of the η′ phase, the solution treatment temperature was set to a level that would increase solubility. As a result, the yield strength was significantly increased through re-precipitation of a large number of fine and uniform η′ phase. In addition, to increase the effect of dissolution, a pre-aging treatment was introduced and the bake hardenability can be improved after dissolution.(Received August 6, 2021; Accepted October 1, 2021) |