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

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-12.8 Y-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.