Tissue Modulation And Toughness Mechanism Of LPSO Structurally Reinforced Mg-Y-Zn-based Magnesium Alloys

The tensile strength of high-strength wrought magnesium alloy can reach 400MPa and the plasticity is 6-10%.However,further improvement of the strength and plasticity of magnesium alloys is still the key to broaden their applications.In particular,Mg-Y-Zn alloy with long period stacking order(LPSO)structure has attracted much attention due to its excellent properties,but it is difficult to balance the strength and plasticity of Mg-Y-Zn alloy,which has become a key scientific problem restricting its wide application.Plastic deformation and alloying are two main ways to effectively improve the strong plasticity of magnesium alloys.Firstly,the morphology and volume fraction of 18R LPSO structure were regulated by adjusting Y and Zn contents.With the increase of Y and Zn contents,the structure of 18R LPSO changes from granular to layered to continuous block,and the volume fraction increases from 12.2%to 54.5%to 65.4%,which leads to the gradual increase of strength and decrease of plasticity of Mg-Y-Zn alloy.Secondly,14H LPSO and DRX grains are dynamically precipitated in the Mg-Y-Zn alloy after hot extrusion,and 18R LPSO grains are banded along the extrusion direction.At the same time,with the increase of Y and Zn content,the 14H LPSO structure content increases gradually,while the grain size and volume fraction of dynamic crystal grain decrease gradually,which makes Mg₉₄Y₄Zn₂alloy show high strength and toughness,and its yield strength,tensile strength and elongation are 305MPa,405MPa and 14%,respectively.Two and three times of as-cast alloy.Furthermore,The Mg₉₄Y₄Zn₂alloy was further Li alloyed,and the Mg₈₉Y₄Zn₂Li₅alloy was hot extruded at different extrusion speeds(Ve=0.4,0.8,1.0,1.2mm/s)and extrusion angles(?=30°,60°,90°)after solution treatment(500?/35h).The results show that the Mg₈₉Y₄Zn₂Li₅magnesium alloy exhibits good strength and toughness under?=30°and Ve=0.4 mm/s,and its compressive yield strength,compressive strength and elongation reach 422 MPa,517 MPa and 16.9%,respectively.The high strength and toughness of the wrought magnesium alloy is mainly due to:fiber strengthening provided by the massive18R LPSO structure arranged along the extrusion direction;The lamellar 14H LPSO structure precipitated in the deformed magnesium matrix and recrystallized grains provided precipitation enhancement.The fine grain strengthening was provided by fine recrystallized grains and the structure of LPSO was strengthened by deformation kinking.In this paper,through Li alloying and hot extrusion deformation of Mg-Y-Zn-based magnesium alloy,the plastic deformation behavior of LPSO structure and its related dynamic recrystallization(DRX)evolution law were studied,the strengthening and toughening mechanism of Mg-Y-Zn-based magnesium alloy was explored,and a new high strength and toughness Mg₈₉Y₄Zn₂Li₅magnesium alloy was prepared.The results can provide theoretical guidance for the preparation and application of high strength and toughness rare earth magnesium alloys.