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Acta Metall Sin  2020, Vol. 56 Issue (7): 1007-1014    DOI: 10.11900/0412.1961.2019.00402
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Effect of Pre-Deformation on Microstructure and Mechanical Properties of Ultra-High Strength Al-Zn-Mg-Cu Alloy After Ageing Treatment
HAN Baoshuai1, WEI Lijun1,2, XU Yanjin1(), MA Xiaoguang1, LIU Yafei1, HOU Hongliang1
1. AVIC Manufacturing Technology Institute, Beijing 100024, China
2. School of Materials Science and Engineering, Beihang University, Beijing 100083, China
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Abstract  

Ultra-high strength Al-Zn-Mg-Cu alloy is a promising lightweight structural material, and there is still room to improve its mechanical property. As a typical precipitation strengthening material, controlling the size and distribution of precipitate is an effective way to enhance the mechanical properties of the ultra-high strength Al-Zn-Mg-Cu alloy. The influence of pre-deformation on the microstructures and properties of the ultra-high strength Al-Zn-Mg-Cu alloy after ageing treatment was studied by TEM, XRD, SEM, DSC and tensile tests. The microstructures and the tensile mechanical properties of Al-Zn-Mg-Cu alloy without pre-deformation and with 3% and 4% pre-deformation were compared. It is found that the pre-deformation can promote the ageing precipitation rate and enhance the precipitate density in the Al-Zn-Mg-Cu alloy, and the pre-deformation ratio of 3% can promote the dispersion of the precipitate phase in the grain interiors, but the pre-deformation ratio of 4% may result in coarsening of precipitate. The size of precipitate along the grain boundaries and the width of precipitation free zones decreased in the pre-deformation treated ultra-high strength Al-Zn-Mg-Cu alloys. The tensile strength and yield strength of the pre-deformation treated ultra-high strength Al-Zn-Mg-Cu alloys increased, and the elongation also increased slightly, in which the tensile strength and elongation of 3% pre-deformation alloy combined with 80 ℃ for 12 h and 120 ℃ for 8 h ageing were (813±4) MPa and 10.10%±0.77%, respectively. The results show that the dislocations produced by pre-deformation may provide more heterogeneous nucleation sites for the precipitate formation, and improve the precipitate's distribution.

Key words:  ultra-high strength Al alloy      pre-deformation      precipitate      precipitation free zone      mechanical property     
Received:  25 November 2019     
ZTFLH:  TG379  
Fund: Defense Industrial Technology Development Program(JCKY2017205B032);National Natural Science Foundation of China(51971206)
Corresponding Authors:  XU Yanjin     E-mail:  xuyj020@avic.com

Cite this article: 

HAN Baoshuai, WEI Lijun, XU Yanjin, MA Xiaoguang, LIU Yafei, HOU Hongliang. Effect of Pre-Deformation on Microstructure and Mechanical Properties of Ultra-High Strength Al-Zn-Mg-Cu Alloy After Ageing Treatment. Acta Metall Sin, 2020, 56(7): 1007-1014.

URL: 

https://www.ams.org.cn/EN/10.11900/0412.1961.2019.00402     OR     https://www.ams.org.cn/EN/Y2020/V56/I7/1007

Sample No.Heat treatment processAbbreviation
1No deformation alloy+80 ℃, 12 h+120 ℃, 8 h12+8
23% deformation alloy+80 ℃, 12 h+120 ℃, 8 h3%+12+8
34% deformation alloy+80 ℃, 12 h+120 ℃, 8 h4%+12+8
4No deformation alloy+80 ℃, 12 h+120 ℃, 10 h12+10
Table 1  Ageing process parameters
Fig.1  XRD spectra (a) and local amplifications (b, c) of the solid solution Al-Zn-Mg-Cu alloy with different deformations
Fig.2  TEM images and SAED patterns (insets) (a, c, e, g), and HRTEM and high magnified images (insets) (b, d, f, h) of the ultra-high strength Al-Zn-Mg-Cu alloys with ageing process parameters of 12+8 (a, b), 3%+12+8 (c, d), 4%+12+8 (e, f) and 12+10 (g, h)
Fig.3  Intergranular precipitates morphologies of ultra-high strength Al-Zn-Mg-Cu alloy under different ageing process parameters (PFZ—precipitation free zone)
(a) 12+8 (b) 3%+12+8 (c) 4%+12+8 (d) 12+10
Ageing process parameterUltimate strength / MPaYield strength / MPaElongation / %
12+8796±5772±79.77±0.51
3%+12+8813±4786±410.10±0.77
4%+12+8807±3781±510.63±0.74
12+10803±2770±89.57±0.66
Table 2  Mechanical properties of ultra-high strength Al-Zn-Mg-Cu alloys under different ageing process parameters
Fig.4  Fracture morphologies of ultra-high strength Al-Zn-Mg-Cu alloy under different ageing process parameters
(a) 12+8 (b) 3%+12+8 (c) 4%+12+8 (d) 12+10
Fig.5  DSC curves of ultra-high strength Al-Zn-Mg-Cu alloys under different ageing process parameters
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