Microstructure Evolution of Extruded Mg-6Gd Alloy Under 175 °C and 150 MPa

doi:10.1007/s40195-018-0817-2

Abstract

Abstract:

The tensile creep behavior of extruded Mg-6Gd alloy, having the tensile yield strength of~110 MPa at 175 °C, has been investigated under 175 °C and 150 MPa. In this study, the extruded Mg-6Gd sample exhibits the total tensile strain of~10.5% after the creep time of 1100 h, and the fast plastic strain of~4.6% at the beginning of the creep test. The microstructure result suggests that the dislocation deformation is the main deformation mode during creep, and the grains with orientation close to〈0001〉|| ED disappear after creep. The creep process containing a low creep strain has no effective promotion for the precipitation compared with the aging process without strain. The origination of creep crack is related to the formation of precipitate-free zone during creep. The work offers an important implication to research the microstructure evolution under an applied stress in a weak aging response Mg alloy.

Key words: Mg-Gd alloy, Texture, Creep, Precipitates, Crack

Rong-Guang Li, Farhan Asghar, Jing-Huai Zhang, Guang-Yan Fu, Qun Liu, Bei-Tao Guo, Yong-Mei Yu, Shu-Guo Guo, Yong Su, Xue-Jiao Chen, Lin Zong. Microstructure Evolution of Extruded Mg-6Gd Alloy Under 175 °C and 150 MPa[J]. Acta Metallurgica Sinica (English Letters), 2019, 32(2): 245-252.

Figures/Tables 12

Fig. 1 Microstructure of the E sample: a OM image along the cross section; b TEM image

Fig. 2 Tensile stress-strain curve of the extruded Mg-6Gd (E sample) alloy at room temperature and 175 °C with a strain rate of 10-3/s

Fig. 3 Creep curve of E sample under 175 °C and 150 MPa

Fig. 4 Misorientation angle distribution graphs derived from EBSD of a E sample, b E+C sample

Fig. 5 EBSD-IPFs of the recrystallized grains referring to the ED for a E sample, b E+C sample; IPF maps of c E sample, d E+C sample, and the reference direction is parallel to TD. The vertical direction is parallel to ED

Fig. 6 IPF maps derived from EBSD of a E sample, b E+C sample containing the recrystallized grains and deformed grains, and the reference direction is parallel to ED. The vertical direction is parallel to ED

Fig. 7 Kikuchi band contrast map derived from EBSD for the E+C sample, and the vertical direction is parallel to ED

Fig. 8 HAADF-STEM images of microstructure of a sample in peak-aged condition, b E+C sample. The electron beam is parallel to the [0001]Mg

Fig. 9 HAADF-STEM images of the E+C sample: a microstructure in the interior of grain containing the fine β′ precipitates, b corresponding FFT of the precipitate contained in red square zone in (a). The electron beam is parallel to the [0001]Mg

Fig. 10 HAADF-STEM images of the E+C sample showing β1 phase: a brighter β1 precipitate connecting with the fine β′ precipitates; b high-magnified image of β1 precipitate, c corresponding FFT of the precipitate contained in site of red square in (b). The electron beam is parallel to the [0001]Mg

Fig. 11 HAADF-STEM image of the E+C sample showing the region of grain boundaries: a low-magnified, b high-magnified images; c microstructure image near the grain boundary, d corresponding EDS mapping of Gd element

Fig. 12 SEM images of the E+C sample near the fracture: a crack morphology mainly in the zone of the elongated grain, b crack morphology mainly in the zone of recrystallized grains, c a high magnification of the crack morphology along the grain boundaries of recrystallized grains

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