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Acta Metall Sin  2020, Vol. 56 Issue (9): 1255-1264    DOI: 10.11900/0412.1961.2020.00004
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Effect of Non-Isothermal Ageing on Microstructure and Properties of 7B50 Aluminum Alloy
LI Jichen1, FENG Di1,2(), XIA Weisheng2, LIN Gaoyong3, ZHANG Xinming3, REN Minwen1
1 School of Materials Science and Engineering, Jiangsu University of Science and Technology, Zhenjiang 212003, China
2 School of Materials Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, China
3 School of Materials Science and Engineering, Central South University, Changsha 410083, China
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Abstract  

Due to the temperature rising or cooling stage in thick plate, non-isothermal ageing has been the research hotspot of heat treatment for Al-Zn-Mg-Cu alloy thick plate. It is possible to replace the isothermal ageing by non-isothermal one because of the high efficiency and practicability. As one of the Al-Zn-Mg-Cu alloy, 7B50 aluminum alloy and its thick plate have supposed to manufacture the wing in "Yun-20" big plane. In this work, hardness test, electrical conductivity test, room temperature tensile test, DSC analysis, exfoliation corrosion test and TEM observation were used to study the influence of non-isothermal ageing on microstructure and corrosion resistance of 7B50 aluminum alloy hot rolling thick plate. Results revealed that, after 480 ℃, 1 h solution and quenched in room temperature water, followed by ageing from room temperature to 215 ℃ at 1 ℃/min heating rate, and furnace cooling to room temperature immediately, the inner precipitates of 7B50 aluminum alloy are fine and dispersed while the ones on grain boundary are coarsened and discontinuous. The tensile strength and exfoliation corrosion grade reached to 605 MPa and EB level, respectively. Comprehensive performance of 7B50 aluminum alloy are excellent overall those of isothermal peak ageing (T6) or isothermal double stages over ageing (T76), but similar to that of retrogression and re-ageing (RRA) treatment. The non-isothermal ageing realized the short process preparation and the measure removing isothermal stage is more suitable for thick plates.

Key words:  7B50 aluminum alloy      non-isothermal ageing      strength      exfoliation corrosion property     
Received:  02 January 2020     
ZTFLH:  TG146.2  
Fund: National Natural Science Foundation of China(51801082);Natural Science Foundation of Jiangsu Province(BK20160560);Undergraduate Innovation and Entrepreneurship Training Program of Jiangsu Province(201910289095Y)
Corresponding Authors:  FENG Di     E-mail:  difeng1984@just.edu.cn

Cite this article: 

LI Jichen, FENG Di, XIA Weisheng, LIN Gaoyong, ZHANG Xinming, REN Minwen. Effect of Non-Isothermal Ageing on Microstructure and Properties of 7B50 Aluminum Alloy. Acta Metall Sin, 2020, 56(9): 1255-1264.

URL: 

https://www.ams.org.cn/EN/10.11900/0412.1961.2020.00004     OR     https://www.ams.org.cn/EN/Y2020/V56/I9/1255

Fig.1  Non-isothermal ageing (NIT) routing
Fig.2  The hardness and electrical conductivity evolution curves during non-isothermal ageing of 7B50 aluminum alloy
Fig.3  Room temperature tensile properties of 7B50 aluminum alloy under different ageing states (Rm—tensile strength, Rp0.2—yield strength, A—elongation)
Fig.4  Bright field TEM images and corresponding SAED patterns along [001]Al (insets) of precipitates in matrix of 7B50 aluminum alloy under ageing states of H160 (a), H215 (b), C25 (c), RRA (d), T6 (e) and T76 (f) (GP—Guinier-Preston zone)
Fig.5  Bright field TEM images of precipitates on the grain boundary of 7B50 aluminum alloy under ageing states of H160 (a), H215 (b), C25 (c), RRA (d), T6 (e) and T76 (f) (PFZ—precipitation free zone )
Fig.6  The exfoliation corrosion morphologies of various ageing states after different etching time
Fig.7  Scheil integral-heating time curve of 7B50 aluminum alloy during non-isothermal heating ageing (S—Scheil integral value of different ageing schedules, Sc—Scheil integral value of a reference ageing schedule)
Fig.8  DSC curves of 7B50 aluminum alloy under different ageing states
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