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Open AccessArticle

Influence of Preaging Treatment on Bake-Hardening Response and Electrochemical Corrosion Behavior of High Strength Al-Zn-Mg-Cu-Zr Alloy

1,2,*, 2,3 and 1,2
1
College of Engineering, Yantai Nanshan University, Yantai 265700, China
2
National Engineering Research Center for Plastic Working of Aluminum Alloys, Shandong Nanshan aluminum Co Ltd., Yantai 265700, China
3
Testing Center, Hang Xin Material Technology Co. Ltd., Yantai 265700, China
*
Author to whom correspondence should be addressed.
Metals 2019, 9(8), 895; https://doi.org/10.3390/met9080895
Received: 24 July 2019 / Revised: 12 August 2019 / Accepted: 13 August 2019 / Published: 15 August 2019
(This article belongs to the Special Issue Phase Transformations in Aluminium Alloys)
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Abstract

The influence of preaging (PA) treatments on the bake hardening (BH) response of a AlZnMgCuZr aluminum alloy which served as automotive body structures were studied in this paper. A novel two-step PA treatment was particularly designed and further employed. The mechanical properties of the alloy were tested in detail. The microstructure was characterized by optical microscope (OM), transmission electron microscopy (TEM) and 3D measuring laser microscope (3D–MLM). Meanwhile, the corrosion behavior was investigated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. The results indicated that the PA treatment was beneficial for the improvement of BH response after baking at 180 °C immediately after the solution treatment and the micro-hardness reached the peak value (194 HV) after 10 h holding, which had a percentage improvement of 110.87% compared to the hardness under the solution condition. The PA treatments decreased natural aging (NA) adverse effects, while it had the lowest NA effect and optimal BH response under 120 °C/20 min. Such a novel two-step PA treatment was revealed further to decrease the NA effect and increase the BH response compared to the optimal PA treatment, in particular, the BH value could reach 168 MPa and was 21.7% higher than that of optimal PA + NA treatment. The optimal corrosion resistance has been shown up by the combined characterizations of potentiodynamic polarization curves, EIS Nyquist plots, and 3D–MLM images. View Full-Text
Keywords: Al–Zn–Mg–Cu–Zr aluminum alloy; bake hardening response; two-step preaging treatment; electrochemical corrosion behavior Al–Zn–Mg–Cu–Zr aluminum alloy; bake hardening response; two-step preaging treatment; electrochemical corrosion behavior
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Li, H.; Liu, X.-T.; Wang, J.-Y. Influence of Preaging Treatment on Bake-Hardening Response and Electrochemical Corrosion Behavior of High Strength Al-Zn-Mg-Cu-Zr Alloy. Metals 2019, 9, 895.

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