| Mg-Zn-Y alloy with long period stacking ordered（LPSO）structure has become a research hotspot in engineering applications and biomedical materials due to its special microstructure and ideal mechanical properties.However,Mg-Zn-Y contains thick dendritic and reticular eutectic W-phase,which limits the improvement of mechanical and corrosion properties.Therefore modification of the microstructure of Mg-Zn-Y alloy has become a research direction.In this paper,micro-alloying element V was added to Mg-Zn-Y alloy system for the first time to study its strengthen mechanism in magnesium alloy with long period stacking ordered structure.The effects of micro-alloying element V on the formation of the microstructure of the alloy in different states（as-cast state,solid solution treatment and extrusion）were investigated by various testing methods,and the effects of each phase of the alloy on the mechanical properties and corrosion properties of the alloy were revealed.The main conclusions are as follows:（1）The as-cast Mg-Zn-Y-（V）alloys mainly consist ofα-Mg matrix,18R LPSO structure(Mg12YZn)and fish-bone W-phase（Mg3Y3Zn2）.By V micro-alloying,the microstructure of Mg-Zn-Y alloy was effectively modified,including grain refinement,decrease of dendritic crystals,increase of 18R LPSO structure,decrease and refinement of W-phase.And the second phase changed from coupled growth to divorced growth.After solid solution treatment,18R LPSO and W-phase gradually dissolved,and W-phase turn to spherify.Lamellar14H LPSO precipitated from the matrix.Through extrusion,the alloy underwent dynamic recrystallization,the grain was further refined,the W-phase was crushed into smaller particles and distributed more evenly.Part of the 18R LPSO and 14H LPSO structure were elongated along the extrusion direction into a fibrous shape.（2）After V micro-alloying,the as-cast improvement of mechanical properties of Mg-Zn-Y-V alloy resulted from microstructure refinement and the compact connection between the second phases.After solid solution treatment,spheroidization of W-phase reduced its adverse effect on mechanical properties.And the precipitation of 14H LPSO structure as well as the solid solution strengthening of element V promoted the improvement of mechanical properties of the alloy.By extrusion,the remarkable microstructure refinement and LPSO kinks can greatly improve the mechanical properties of the alloy.The ultimate tensile strength and elongation of the alloy after V microalloying,solid solution treatment and extrusion were 307 MPa and 20%,respectively,which were 103%and 111%higher than that of the as-cast Mg-Zn-Y alloy.（3）After V micro-alloying,the second phase in the as-cast alloy changes from coupled growth to divorced growth,the second phase is more compact arranged,which will hinder the contact of simulated body fluid with internal metal.In addition,the presence of V and the grain refinement after micro-alloying make the corrosion product film more stable,which is conducive to improving the corrosion resistance of the alloy.The precipitation of 14H LPSO structure after the solution treatment makes the product film denser and protective.In addition,the W-phase spheroidization makes the invasion channel of the simulated body fluid closed,so the corrosion resistance of the alloy is improved.By increasing the speed of extrusion,the dynamic recrystallization volume fraction increases,the microstructure uniformity increases,the cathode effect of W-phase weakens after it is crushed into tiny particles,the corrosion pattern of the alloy tends to be uniform corrosion,and the corrosion resistance is greatly improved.After V micro-alloying,solid solution treatment and extrusion,the weight loss rate of the alloy was 1.93 mmy-1,which was 85%lower than that of the as-cast Mg-Zn-Y alloy. |
