Mg alloys, the lightest structural metal, generally suffer from low strength and poor deformability, and therefore severely restrict their widespread applications in automotive, aircraft, and aerospace industries. [1] The underlying reason for such mechanical behaviors is the anisotropic response inherent in the hexagonal close-packed (hcp) lattice of Mg. [2-3] Therefore, the key of advancing their applications is reducing the anisotropic behavior of different deformation modes, through regulating the relative activities of (easy) basal slips, (hard) non-basal slips, and twinning.

Herein, we demonstrate the new microstructure, the self-assembled hexagonal 1-nm Gd nano-fibers pattern within binary Mg-Gd alloys. [4] As shown in Fig.1, such hexagonal patterns are typically a few hundred nanometers in width and a few microns in length. These patterns are associated with dislocation templates. Such patterns include Gd-segregated dislocations with approximately 1 nm in diameter, which have a c-rod shape, and these in turn become effective inhibitors for basal slips since they have to cut these nano-fibers. On the other hand, non-basal slips suffer much less effect because the glide of non-basal dislocations has much less chances of cutting these Gd-segregations. Thus, these patterns can strengthen Mg alloys mainly through pinning basal dislocations; more importantly, tune the relative activities of basal and non-basal slips, and thus improve the deformability of Mg alloys. It is also worth mentioning that such patterning structure can be synthesized through a generally economical hot extrusion approach.

In summary, 1-nm Gd nano-fibers, with c-rod shape, are self-assembled into hexagonal patterns in Mg matrix, which can tune the relative activities of deformation modes and thus improve mechanical properties of Mg alloys. Our results open up a new path of engineering advanced Mg alloys though manipulating their microstructure.

References:

[1] I. J. Polmear, Light Alloys, 4^th ed., Elsevier/Butterworth-Heinemann, Oxford, U.K., 2006.

[2] J. Koike, Acta. Mater. 51(2003), p. 2055-2065.

[3] J.-F. Nie, Metall. Mater. Trans. A 43(2012), p. 3891-3939.

[4] Y.X. Li, et al, (submitted).

Acknowledgments

We acknowledge the financial support from 1000Plan Professorship for Young Talents Program and the National Science Foundation of China (No. 51401124). We are grateful for the TEM specimens prepared by M. Shao and L. Jin. 

Figures:

Figure 1. Gd nano-fiber patterns in Mg. (A) The TEM-BF image. White arrows indicate the Gd nano-fiber patterns. (B) The STEM-HAADF image. Gd shows as bright contrast due to the large atomic number differences between Gd and Mg. These Gd-segregations are patterned in a hexagonal shape with identical interspacing.

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