Achieving ultra-high strength using densely ultra-fine LPSO phase

doi:10.1016/j.jmst.2022.04.036

Abstract

Abstract:

Long period stacking ordered (LPSO) structures are an effective strengthening phase in Mg alloys. However, the coarse LPSO phases in as-cast alloys are very difficult to refine, and they dramatically reduce the strengthening effect. In the present study, friction stir processing (FSP) was employed to refine the structure of an Mg-12.8Y-4.7 Zn (wt%) alloy with a very high content of coarse LPSO phases. An optimized FSP regime refined the coarse LPSO phases into densely ultrafine blocks with an average width of ∼200 nm and an average length of ∼1 μm. An ultrahigh yield strength of ∼800 MPa was achieved under compression of the FSP region. Theoretical calculations indicated that the strengthening by the densely ultrafine LPSO phases was up to approximately 630 MPa.

Key words: Mg alloys, Strengthening, LPSO, Grain refinement

Changzheng Li, Huan Liu, Yunchang Xin, Bo Guan, Guangjie Huang, Peidong Wu, Qing Liu. Achieving ultra-high strength using densely ultra-fine LPSO phase[J]. J. Mater. Sci. Technol., 2022, 129: 135-138.

Figures/Tables 5

Fig. 1. (a) Cross sectional ECC images of 1300-5 FSP samples and high magnification views of (b) initial zone, (c) transition zone, and (d) pin-driven zone.

Fig. 2. (a) ECC image for the pin-driven zone in sample 1300-5 and (b) width and (c) aspect ratio (length/width) of LPSO particles.

Fig. 3. (a) Bright-field TEM images of precipitates at the pin-driven zone in sample1300-5 sample; high-magnification views and corresponding selective area diffraction patterns of (b) 18R and (c) 14H; Fourier-filtered high-resolution images for (d) 18R and (e) 14H. The schematic diagrams show the structures of 18R and 14H.

Fig. 4. (a) True strain-stress curves under compression of micropillars in pin-driven zone and initial zone; SEM images for the micro pillars in (b) pin-driven zone and (c) in initial zone without LPSO.

Table 1. Values of the parameters used for the calculation of the Orowan mechanism.

Parameter	d_p (μm)	l_p (μm)	t_p (μm)	f (%)
Value	0.34	0.77	0.24	54

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