Research for Long-Period Structure in Mg Alloy using High Pressure

As represented by long-period stacking ordered structure (LPSO), long-period phase based on hcp-Mg lattice are received attention as new kind strengthening phase of Mg alloy. We have researched formation process of LPSO and new types of long period phase based on hcp-Mg lattice using high pressure experiment technique. For the formation process of LPSO, we found hcp-Mg lattice transformed to LPSO after the lattice expansion of hcp due to invasion of Y. This result was interpreted together with the result of the first-principles calculation, and then a model of the formation process of LPSO was proposed. On the other hand, we worked on development for long-period superlattices based on hcp-Mg lattice other than LPSO. As the results, two types of longperiod superlattices (LPSLs) based on the hcp-Mg lattice were found in Mg97Yb2Zn1 after subjected at 5 GPa: one LPSL is the Mg14Yb3Zn1 phase, whose unit cell dimensions are described as 3× 3×3 with respect to those of the original a-Mg lattice; the other LPSL is the Mg17Yb4Zn3 phase, whose unit cell dimensions are described as 3× 3×2 with respect to those of the original hcp-Mg lattice. These findings using high pressure technique can use in the development of Mg alloy at ambient pressure. [magnesium alloy, long-period superlattice, long-period stacking ordered structure, high pressure treatment, transmission electron microscope]