Microstructure And Mechanical Properties Of Hot-Extruded Mg-4%Zn-0.5%Zr-xCe Alloys

Magnesium alloy have such characteristics as low density, high specific stiffness as akind of light metal structural materials, and have found a wide application in aeronauticsand astronauts industries, military industry and traffic field. To extend their applicationfield, magnesium alloys prepared with hot extrusion technology have received more andmore attention. The Mg-Zn-Zr series alloys are a typical kind of wrought magnesiumalloys. In this investigation, as-extruded Mg-Zn-Zr-Ce alloys were taken as experimentalmaterials and the tensile and low-cycle fatigue tests were performed in order to determinethe influence of rare earth element Ce and aging treatment on the mechanical properties ofhot-extruded Mg-4%Zn-0.5%Zr-xCe magnesium alloys and to offer the reliable theoreticalreference for developing new magnesium alloys with high strength and ductility.The microstructural observations reveal that the addition of Ce with appropriatecontent can refine the grains of the extruded Mg-4%Zn-0.5%Zr-xCe alloys. The results oftensile experiments show that the addition of Ce with appropriate content can significantlyenhance the ultimate tensile strength, yield strength and elongation of the extruded Mg-4%Zn-0.5%Zr-xCe alloys. Especially, the mechanical properties of the alloys getobviously enhanced after aging treatment. The results of low-cyclic fatigue tests show thatduring fatigue deformation, the extruded Mg-4%Zn-0.5%Zr-xCe alloys exhibit the cyclicstrain hardening, softening and stable cyclic stress response. In addition, the addition ofrare earth element Ce with appropriate content can prolong the low-cycle fatigue lives ofthe hot-extruded Mg-4%Zn-0.5%Zr-xCe alloys. For the hot-extruded Mg-4%Zn-0.5%Zr-xCe alloys with different Ce contents, the relationship between the elastic strain amplitudeand reversal cycles to failure is linear, and can be well described by the Basquin equation.Meanwhile, the relationship between the plastic strain amplitude and reversal cycles tofailure also exhibits a linear behavior and obeys the Coffin-Manson equation. The observations on the fracture surfaces reveal that under tensile loading condition, theextruded Mg-4%Zn-0.5%Zr-xCe alloys mainly exhibit the mixed brittle and ductile rupture.Under the low-cycle fatigue loading condition with total strain control mode, the fatiguecracks initiate in a transgranular mode at the free surface of fatigue specimens andpropagate transgranularly for the hot-extruded Mg-4%Zn-0.5%Zr-xCe alloys.