Effect Of Rare Earth Content And Extrusion Process On The Microstructure And The Corresponding Mechanical Properties Of Mg-Gd-Er-Zn Alloys

Magnesium alloy,as the lightest metal structural material at present,has the advantages of low density,high specific strength and specific rigidity,and excellent damping performance.And it shows a very broad application prospects in aerospace,defense and military industry,and transportation fields that have higher demand for lightweight.However,due to its low absolute strength and poor ductility at room temperature,the industrial application of magnesium alloys is greatly limited.Therefore,the development of wrought magnesium alloy with excellent mechanical properties and understanding its the plastic deformation behavior at room temperature have important academic significance and practical value for the development of novel high-toughness wrought magnesium alloy and large-scale application of wrought magnesium alloys.In this paper,based on Mg-1.5Zn alloy,Mg-Gd-Er-Zn alloys were prepared by adding equal mass of rare earth（Gd,Er）.The effects of the content of rare earth（Gd,Er）and the extrusion process on the microstructure and properties of the Mg-Gd-Er-Zn alloys were investigated.Finally,a wrought magnesium alloy with excellent mechanical properties was prepared and its plastic deformation behavior at room temperature were discussed.The as-cast Mg-Gd-Er-Zn alloy mainly consists ofα-Mg and W phases（Mg₃Zn₃（Gd,Er）₂）.When the content of rare earth（Gd,Er）exceeded 4wt.%,the LPSO phase was formed in the as-cast alloy.After 450°C heat treatment,the skeletal W phase in the as-cast Mg-4Gd-4Er-1.5Zn（GEZ41）and Mg-6Gd-6Er-1.5Zn（GEZ61）alloys was transformed into the LPSO phase;when the temperature was increased to 500°C,the skeletal W phase was directly spheroidized.With the increase of rare-earth（Gd,Er）content,as-extruded Mg-Gd-Er-Zn alloys obtained a uniform and fine dynamic recrystallization structure,the basal texture was significantly weakened,and the c-axis of most grains were gradually aligned with the extrusion direction,forming a"rare earth texture"of<0001>∥ED;The mechanical properties and yield asymmetry of as-extruded Mg-Gd-Er-Zn alloys were improved due to the solid solution strengthening,fine grain strengthening and texture weaken.The morphology of second phase has an important influence on the microstructure and properties of as-extruded GEZ41 alloy.The bulk LPSO phase can promote dynamic recrystallization and leads to a weak basal texture,which is conducive to good ductility.And the lamellar LPSO phase would seriously inhibit the dynamic recrystallization.It results in decreasing the degree of recrystallization and the formation of a strong basal texture,which contributes to enhancement of the strength.The introduction of finely dispersed second-phase particles can bring about uniform and fine recrystallized structure and weaken the basal texture,which leads to excellent comprehensive mechanical properties.On the basis of above,a more uniform and fine recrystallized structure was obtained by increasing the extrusion ratio.The as-extruded GEZ41 alloy exhibits excellent mechanical properties:tensile/compressive strengths are 335 MPa and513 MPa,tensile/compressive yield strengths are 295 MPa and 309 MPa,and tensile/compressive elongations are 27.6%and 16.0%,respectively.Grain size and texture have an important influence on the strain hardening behavior of as-extruded Mg-Gd-Er-Zn alloys during tension and compression.With the weakening of basal texture,the twinning is inhibited and the basal slip acts as the dominant deformation mechanism,which slowed down the rate of strain hardening rate.As the grain size decreases,the activation of non-basal slip would decrease the strain hardening rate.The main deformation mechanisms of the as-extruded GEZ41 alloy are the prismatic slip and the basal slip during tension.With the increase of the tensile strain,the prismatic slip was further activated.While under compression,the main deformation mechanisms the as-extruded GEZ41 alloy are prismatic slip,basal slip and extension twinning.And with the increase of compressive strain,the combined effect of slip and extension twinning make more the c-axis of grains parallel to the compressive direction,which leads to the formation of a relatively strong<0001>texture.