Effect Of Cd On Microstructure And Property Of Mg-Zn-Y-Mn Alloys Cotaining LPSO Phase

Magnesium alloys,as candidate metals for structural materials,were widely used in aerospace,automotive and electron industry and attracted much attention due to their high specific and light-weightiness,while its structural applications is restricted by the the shortcoomings of its mechanical properties,such as low absolute strength,hardness and plasticity.The Mg-Zn-Y magnesium alloy containing a long period stacking ordered structure?LPSO?have been received attention because of good heat resistance,high tensile strength and plasticity.In generally,the higher Y/Zn ratio is a necessary condition for the formation of the LPSO phase,but it would increase the cost.Therefore,it is one of the key problems to be solved to find a low-cost element to obtain a high-performance magnesium alloy.The effects of Cd additions on the microstructure and mechanical properties of Mg₉₄Zn_2.5Y_2.5Mn₁ alloy were investigated and the related mechanisms were discussed in this paper.Firstly,Mg-Zn-Y-Mn-?Cd?alloys were prepared by conventional casting and the role of the element Cd was investigated in this system.The influence of electromagnetic stirring process,solution temperature,solution time and cooling method on the microstructure and properties of Cd-containing magnesium alloy were analyzed.High-performance magnesium alloy was prepared by extrusion to investigate the effect of temperature on the microstructure,dynamic recrystallization and properties of extrusion deformation.In this paper,the solidification process and the growth pattern of the second phase growth mode in this system are described for the first time,and the dynamic recrystallization mechanism and strengthening mechanism are discussed.This article provides ideas for the preparation of high strength magnesium alloys.The research results are as follows:?1?The phase composition of the as-cast Mg-Zn-Y-Mn-Cd alloy mainly consists of?-Mg,W phase?Mg₃Zn₃Y₂?and LPSO phase(Mg₁₂Zn₁Y₁).Proper Cd addition can effectively refine the microstructure and promotes the formation of 18R-LPSO phase and effectively suppresses the formation of W phase.During the solidification process,the growth pattern of the second phase of the alloy gradually changes from the coupled growth pattern to the divorced growth pattern.The optical mechanical properties are obtained with addition of Cd.?2?During the solution treatment,part of the 18R-LPSO phase dissolves,the W phase spheroidizes and the thin stripes 14H-LPSO phase precipitates from the magnesium matrix.The solution treatment can improve the strength and plasticity of the alloy and prepare the structure for the later extrusion deformation.?3?Electromagnetic stirring makes the distribution of alloy elements more uniform,which can refine grains and promote the formation of 18R-LPSO phase.Besides,the solution treatment time Electromagnetic stirring can shorten and achieve the solution treatment effect in advance.?4?Dynamic recrystallization behavior was obvious in Mg-Zn-Y-Mn-?Cd?alloy during hot extrusion process.The dynamic recrystallization?DRX?behavior during hot extrusion deformation processes leads to grain refinement,which is more effective for magnesium alloys in improving the mechanical properties.