Effects of pre-strain and ageing on the LPSO structure in Mg₉₇Zn₁Y₂ alloy

The effects of pre-strain and ageing on the LPSO structure in Mg₉₇Zn₁Y₂ alloy were investigated by electron microscopy. It is found that 14H type LPSO structure evenly precipitates from the supersaturated matrix during ageing of solutionized sample. This LPSO structure is observed even at the early stage of ageing, and no precursor phase such as 18R is observed before 14H forms. The 14H structure is kept after a long time ageing. Similar results have been found for ageing of pre-strained sample. Moreover, it shows that the pre-strain could reduce the LPSO plate spacing, since the LPSO plate with one or two structure units increased due to deformation. In both un-deformed and deformed cases, LPSO plate grows by ledge mechanism. The cooperative motion of the structure units in the growth ledge may be due to the elastic interactions between the structure units.