Microstructural Evolutions of AA7055 Aluminum Alloy Under Dynamic and Quasi-static Compressions

doi:10.1007/s40195-014-0041-7

Abstract

Abstract:

The microstructural evolution of AA7055 aluminum alloy under dynamic impact loading with the strain rate of 1.3 × 10⁴ s^-1 controlled by a split Hopkinson pressure bar was investigated, and compared with that under quasi-static mechanical loading in compression with strain rate of 1.0 × 10^-3 s^-1. The quasi-static-compressed sample exhibited equiaxed dislocation cells, which were different from the elongated and incomplete dislocation cells for the alloy undergoing dynamic compression. The high strain-rate compression also induced the formation of localized shear bands in which the recrystallizations characterized as fine equiaxed grains were observed. The microstructural evolutions under both quasi-static and dynamic compressions are rationalized in terms of the dislocation cell model combined with the dislocation kinetics, in addition to the adiabatic temperature rise in shear bands at high strain rate.

Key words: Aluminum alloy, Microstructural evolution, Dynamic impact loading, Dislocation cell, Recrystallization

Yuanyuan Xiong, Ning Li, Huawen Jiang, Zhigang Li, Zhu Xu, Lin Liu. Microstructural Evolutions of AA7055 Aluminum Alloy Under Dynamic and Quasi-static Compressions[J]. Acta Metallurgica Sinica (English Letters), 2014, 27(2): 272-278.

Figures/Tables 5

Fig. 1 SEM micrographs of the AA7055 aluminum alloy before a, after b annealing at 520 °C for 90 min (RD rolling direction)

Fig. 2 True stress versus strain curves for the AA7055 aluminum alloy under quasi-static (strain rate 1.0 × 10-3 s-1) and dynamic (strain rate 1.3 × 104 s-1) compressions

Fig. 3 Transmission electron micrographs of AA7055 aluminum alloy after quasi-static (a strain rate of 1.0 × 10-3 s-1, equiaxed dislocation cells) and dynamic (b strain rate of 1.3 × 104 s-1, elongated and incomplete dislocation cells) compressions

Fig. 4 Transmission electron micrographs of AA7055 aluminum alloy after dynamic compression: a–c localized shear band, d magnified micrograph of c, showing recrystallization characterized as nanoscale equiaxed grains

Fig. 5 Schematics of the formation of dislocation cell structure: a origin and moving of dislocation “1S,” b a jog is trapped at E, cross-slip happened and screw dislocation moving along the direction v, c dislocation continuously moving, and d dislocation cell is formed when slips are terminated at the obstacles (in the regions of AD and DC) and secondary slip occurs

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