Effect Of Processing Technology On Mechanical Properties And Corrosion Behavior Of Medical Mg-Zn-Y-Nd-Zr Alloy

Magnesium alloys have attracted extensive attention in the field of orthopaedic implants due to its biodegradability and good biocompatibility.However,as an orthopaedic implant material,it needs to serve in complex physiological environment.The insufficient mechanical properties,poor toughness and ductility,and fast degradation rate of Mg alloys would lead to premature failure and secondary fracture of bone.Thus,severely limits the application of the alloy as orthopaedic implant material.Therefore,it is of great theoretical and practical significance to study the mechanical properties and corrosion resistance of Mg alloys after different mechanical processing and aging treatment.In this paper,the microstructure,mechanical behavior and corrosion behavior of Mg-2Zn-0.6Y-0.5Nd-0.3Zr and Mg-4Zn-0.8Y-0.5Nd-0.3Zr alloy after one and two passes of extrusion,as well as the one-pass extruded Mg-4Zn-0.8Y-0.5Nd-0.3Zr alloy after aging treatment were studied systematicly,and the mechanical fracture mechanism and corrosion mechanism were explained.The microstructures of the as-cast,one-pass extruded and two-pass extruded Mg-2Zn-0.6Y-0.5Nd-0.3Zr and Mg-4Zn-0.8Y-0.5Nd-0.3Zr alloys were observed.The results show that the microstructures of the Mg alloys with three different states were all composed of aMg matrix and W phase.The equiaxed grain sizes of the two as-cast alloys were about 35?m.After one-pass extrusion,incomplete dynamic recrystallization occurred in the alloy.The average size of the equiaxed dynamic recrystallization(DRXed)grains of one-pass extruded Mg-2Zn-0.6Y-0.5Nd-0.3Zr and Mg-4Zn-0.8Y-0.5Nd-0.3Zr alloy were 4.93?m and 2.48?m,respectively.Dynamic recrystallization occurs again during the two-pass extrusion process.The average size of the equiaxed DRXed grains of Mg-2Zn-0.6Y-0.5Nd-0.3Zr and Mg-4Zn-0.8Y-0.5Nd-0.3Zr alloys after two-pass extrusion were 1.56?m and 1.25?m,respectively.The above results show that hot extrusion process can effectively refine the microstructures of Mg alloy,and the increase of Zn content can further refine the microstructures of the alloy.Tensile and compressive tests were carried out at room temperature on the as-cast,onepass extruded and two-pass extruded Mg-2Zn-0.6Y-0.5Nd-0.3Zr and Mg-4Zn-0.8Y-0.5Nd-0.3Zr alloys,respectively,and the tensile and compressive direction were parallel to the extrusion direction.The experimental results show that the tensile and compressive strength of the two alloys after one-pass extrusion were obviously higher than those of the as-cast alloys.The tensile and compressive strength of the two-pass extruded alloys were higher than those of the one-pass extruded alloys.After the same treatment process,the mechanical properties of the Mg-4Zn-0.8Y-0.5Nd-0.3Zr alloy were better than those of the Mg-2Zn-0.6Y-0.5Nd-0.3Zr alloy.The electrochemical experiments were carried out on the as-cast,one-pass extruded and two-pass extruded Mg-2Zn-0.6Y-0.5Nd-0.3Zr and Mg-4Zn-0.8Y-0.5Nd-0.3Zr alloys.The experimental results show that the corrosion current densities of the two Mg alloys both decreased after one-pass extrusion and two-pass extrusion.The immersion experiments were carried out in Hank's solution on Mg-2Zn-0.6Y-0.5Nd-0.3Zr and Mg-4Zn-0.8Y-0.5Nd-0.3Zr alloys with three states.The results showed that the corrosion rates of the one-pass extruded alloys were significantly lower than that of the as-cast alloys,and the corrosion rates of the two-pass extruded alloys were further reduced.The one-pass extruded Mg-4Zn-0.8Y-0.5Nd-0.3Zr alloy was aged at 200??225? and 250? for different time.The microstructures of the alloy after different aging treatment were observed,and their mechanical properties and corrosion resistance were characterized.The results show that the size of the equiaxed grains of the one-pass extruded Mg-4Zn-0.8Y-0.5Nd-0.3Zr alloy decreases firstly and then increases with aging time at different aging temperatures.The corrosion rate of the alloy after aging for different time in 200? and 250? was lower than that in one-pass extrusion condition.