Study On Microstructures,Mechanical Properties,and Corrosion Resistances Of Mg-4Y-xZn Alloy

WZ（Mg-Y-Zn）alloy is a kind of alloy system which has attracted much attention in the field of magnesium alloys.The research work on WZ alloy has great theoretical and practical significance.Based on Mg-4Y alloy,the effect of Zn content on Mg-Y-Zn alloy was studied in this paper.The effects of different processes such as solid solution time,solid solution temperature and aging method on the microstructure and properties of Mg-4Y-xZn alloy were studied.The results of the cast alloy study show that when the content of Zn is 1wt.%,the three element phase of the alloy is X phase(Mg₁₂ZnY),and the X phase is the strip shape along the grain boundary.When the Zn content rises to 2wt.%,the phase of the alloy is still X phase,but the X phase distributes along the grain boundary with a needle like structure.When Zn content rises to 3wt.%,the new ternary phase appears in the alloy——W phase（Mg₃Zn₃Y₂）.The triangulation of grain boundary is short rod like.With the increase of Zn content and the increase of 4wt.%content,the X phase disappeared and the W phase structure at the junction of grain boundaries was more developed.With the increase of Zn content,the hardness of the alloy increases continuously.The tensile strength and elongation of the alloy at room temperature and high temperature increased first with the increase of Zn content from 1%to 3%,and then decreased when the content of Zn reached 4%.When the content of zinc increases from1%to 2%,the reason for cleavage fracture of the alloy is cleavage fracture to quasi cleavage fracture,and then when the Zn content reaches 4%,the fracture mechanism becomes a cleavage fracture again.With the increase of Zn content,the corrosion rate of the alloy increases first and then decreases,and the corrosion rate is the largest when zinc is 3%.When the soaking time was extended to 16h,the corrosion resistance of the alloy increased gradually.The best corrosion resistance of WZ43 was found when the immersion was 16h.After treatment with T4,the three element phase of the alloy changed significantly.With the change of solid solution temperature and time,when the solution temperature and solution time reach the best,the W phase gradually disappears,but for WZ41,WZ42 and WZ43 alloys,there are still some long period ordered phases（LPSO）which are not completely soluble,and distribute along grain boundaries.At the same time,the 18R type LPSO phase in the alloy gradually changed into 14H structure by solution treatment.After solution treatment,the strength of WZ41,WZ42,WZ43,and WZ44 increased,the hardness of alloys decreased,the plasticity of four kinds of alloys increased significantly,and WZ42 alloy exhibited the best strength.After solid solution treatment,the corrosion rate of the alloy decreased with the increase of Zn content,and the corrosion resistance of the alloy increased with the increase of Zn content after soaking for 8h.The microstructure of the aged Mg-Y-Zn alloy is composed ofα-Mg+MgZn+Mg₂₄Y₅,and some undissolved LPSO phase in the solid solution process.After aging treatment,the peak hardness of the alloy is higher than that of the cast state and the solid solution state,and the optimal aging treatment process is 200°C×12h.At the same time,the strength has been greatly improved compared with the cast and solid solution states.The plastic phase of the alloy is slightly lower than that of the solid solution.After T6 treatment,the corrosion rate of alloy first decreased with the increase of Zn content.When the Zn content reached 4%,the corrosion rate increased and WZ43 showed the smallest corrosion rate.The results of EIS fitting after 8h immersion showed that the corrosion resistance of the alloy decreased with the increase of Zn content.