Microstructure Evolution and Dynamic Precipitation Behavior of Mg–10Gd–4Y–1Sm–0.5Zr Alloy During Backward Hot Extrusion

The microstructure evolution and dynamic precipitation behavior of Mg–10Gd–4Y–1Sm–0.5Zr alloy during backward hot extrusion are studied. The results show that the equiaxed grains become polygonal grains and fine DRX grains are generated which form a “necklace structure” along the initial deformed grain boundaries. With further increase of deformation, DRX grains volume fraction significantly increases and finally almost fully DRX extruded microstructure is obtained in the completely hot-extruded sample. The extrusion deformation results in increase of dislocation density and formation of dislocation cells. The subgrain boundaries continue to absorb dislocations and finally change from the low angle grain boundaries to the high angle grain boundaries. Hot extrusion deformation results in formation of dynamic precipitated phase, β phase particle, i.e., Mg₅(Gd,Y) phase, with diameter of 45–145 nm, which is incoherent relationship with the matrix. In process of increasing deformation, the shape of β phase changes from spindle shape to disc shape and the distribution of β phase transforms from strip distribution along grain boundary to discrete distribution.