Effects of pre-treatments on precipitate microstructures and creep-rupture behavior of an Al-Zn-Mg-Cu alloy
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-Wei Wang and Dao-Guang He Light Alloy Research Institute of Central South University, Changsha 410083, China
Ying Zhou School of Mechanical and Electrical Engineering, Central South University, Changsha 410083, China
Ming-Song Chen School of Mechanical and Electrical Engineering, Central South University, Changsha 410083, China; and State Key Laboratory of High Performance Complex Manufacturing, Changsha 410083, China
Ming-Hui Huang School of Mechanical and Electrical Engineering, Central South University, Changsha 410083, China; Light Alloy Research Institute of Central South University, Changsha 410083, China; and State Key Laboratory of High Performance Complex Manufacturing, Changsha 410083, China
Jin-Long Zhang School of Mechanical and Electrical Engineering, Central South University, Changsha 410083, China; and State Key Laboratory of High Performance Complex Manufacturing, Changsha 410083, China (Received 28 November 2015; accepted 21 March 2016)
The effects of pre-treatments on the precipitate microstructures of an Al–Zn–Mg–Cu alloy are investigated. Meanwhile, the creep-rupture behavior of the under-aged and peak-aged alloys are comparatively analyzed. Additionally, the effects of pre-treatment on the fracture mechanisms are discussed. It is found that the precipitate microstructures are sensitive to pre-treatments. The intragranular precipitates of the peak-aged alloy are larger than those of the under-aged. The precipitate free zone of the peak-aged alloy is wider than that of the under-aged. Some large intergranular precipitates appear on the grain boundaries of the under-aged alloy, and induce the nucleation of microvoids. Eventually, the creep fracture of the under-aged alloy is accelerated. Therefore, the differences in microstructures lead to the shorter creep-rupture life of the under-aged alloy, compared to the peak-aged alloy.
I. INTRODUCTION
Contributing Editor: Jürgen Eckert a) Address all correspondence to this author. e-mail: [email protected], [email protected] DOI: 10.1557/jmr.2016.144
microstructures. Some studies12–16 show that intragranular precipitates can be dispersed and refined when the Al–Zn–Mg–Cu alloys were heat treated in T6 temper. Moreover, previous investigations17–20 found that the discontinuously-distributed intergranular precipitates and refined intragranular precipitates can be obtained by the retrogression and re-ageing treatments. Furthermore, the effects of stress-aging treatment on precipitates were investigated by Lin et al.,21,22 and they found that the amount of aging precipitates and the width of precipitate free zone (PFZ) increase with the increase of creep aging temperature and external stress. Generally, the service life of structural components working at high temperature conditions is determined by the creep resistance of aluminum alloys.23–27 In recent years, some researchers devoted to studying the creep behaviors of Al–Zn–Mg–Cu alloys. Mahathaninwong et al.28 discussed the effects of pre-treatment on the creep-rupture behaviors of semi-solid casted
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