Research On Microstructure And Mechanical Properties Of Low-alloyed Mg-Sn-Ca-Mn Alloys

In the background of times,magnesium alloy,as the lightest metal structural material,has been widely concerned and applied in many fields,especially in the areas of transportation,aerospace,and national defense,and has gradually become one of the most important alternative materials in lightweight structural design.However,due to the magnesium alloys'shortcomings,such as low absolute strength and poor plastic deformation ability at room temperature,the magnesium alloys'practical application is still greatly restricted.Compared with traditional cast magnesium alloys,wrought magnesium alloys are superior in strength,dimensional accuracy,and ductility.Nonetheless,there are still relatively few types of wrought magnesium alloys.Especially the development and research of magnesium alloys with low cost,excellent performance,and good forming properties are lagging,which limits the promotion and application of magnesium alloys.In response to the above problems,this academic dissertation adds low-cost alloying elements Mn,Al,and Zn to the low alloyed Mg-Sn-Ca-based alloys and designs the alloy's composition.The low alloyed Mg-Sn-Ca-Mn-Al/Zn wrought alloys were prepared by the conventional casting method and traditional deformation extrusion process.We systematically studied the influence of different Mn,Al,Zn alloying elements on the microstructure and mechanical properties of alloys.The main research results are as follows:(1)The effect of different Mn content on the microstructure of as-cast Mg-Sn-Ca-based alloys was studied.The result has shown that increasing the addition of Mn could inhibit the nucleation of the CaMgSn hard phase,promote the formation of Mg₂Ca,improve the extrusion performance of the alloy,and improve the microstructure and comprehensive mechanical properties of the alloy.The room temperature yield strength of the extruded Mg-1Sn-1Ca-0.5Mn(wt.%)alloy is 229 MPa,the tensile strength is 250 MPa,and the elongation is 18.6%.(2)The influence of the Al element on the microstructure and mechanical properties of Mg-Sn-Ca-Mn-based alloys was systematically studied.The research results have shown that the addition of Al promotes the nucleation of the CaMgSn phase and causes the C14-Mg₂Ca phase to transform to the C36-(Mg,Al)₂Ca phase.Through the PSN mechanism,the synergistic effect of the nano Al₈Mn₅phase,the nano Al₂Ca phase,and the broken sub-micron CaMgSn phases promotes the dynamic recrystallization of the alloy and refines the grains.The analysis shows that the ultra-fine grains,abundant second phases and strong texture make the as-extruded alloy exhibit excellent mechanical properties.Among the alloys,the as-extruded Mg-1Sn-1Ca-0.5Mn-1.5Al(wt.%)alloy has the most excellent mechanical properties,and its room temperature yield strength,tensile strength and elongation reached296 MPa,303 MPa and 9.6%,respectively.(3)The mechanism of the effect of Zn addition on the microstructure and mechanical properties of Mg-Sn-Ca-Mn-based alloys is revealed.Studies have shown that trace amounts of Zn promote the formation of the CaMgSn phase.With the further increase of Zn addition,it will assist the formation of the Mg₂Ca phase.After hot extrusion processing,the structure of the as-extruded alloy is composed of the CaMgSn phase,nano-Mg₂Ca phase,and nano-?-Mn phase.Due to the significant promotion effect of submicron CaMgSn relative to dynamic recrystallization,the as-extruded Mg-1Sn-1Ca-0.5Mn-1.0Zn(wt.%)alloy exhibits the best mechanical properties,its yield strength,tensile strength,and The elongation is 213 MPa,260MPa,and 22.55%,respectively.