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.
Highlights
Lightweight has become an important direction for the development of automobiles [1]
The results indicated that the PA treatment was beneficial for the improvement of bake hardening (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
In regards to aluminum for lightweight automotive development, previous studies were mainly focused on the research of 6000 series aluminum for panels, such as the subduction of detrimental natural aging (NA) effect and the enhancement of bake hardening (BH) response [7,8]
Summary
Lightweight has become an important direction for the development of automobiles [1]. In regards to aluminum for lightweight automotive development, previous studies were mainly focused on the research of 6000 series aluminum for panels, such as the subduction of detrimental natural aging (NA) effect and the enhancement of bake hardening (BH) response [7,8]. They are not competitive with respect to current high strength steels for structural components. The optimization of heat treatment to eliminate the NA effect and improve BH response is dramatically demanded, and its influence on corrosion resistance is needed in order to study more extensive applications of 7000 series aluminum in automotive body structures. The corrosion behavior was fully characterized by potentiodynamic polarization curves, electrochemical impedance spectroscopy (EIS), Nyquist plots and 3D measuring laser microscope (3D–MLM) images
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