The Effect Of Hot Deformation On Microstructure And Mechanical Properties Of Mg-Zn-Gd-Ca Alloy

In present investigation,Mg-4Zn-0.5Ca-xGd?x=0,0.5,1 and 2 wt.%?alloys were fabricated with different addition of Gd content,and followed by hot deformation.The effects of hot deformation process on microstructure and mechanical properties of Mg-Zn-Gd-Ca alloy were investigated systematically.The results of investigation inlustated that the secondary phase of as-casted Mg-4Zn-0.5Ca alloy was the lamellar MgZn₂ and distributed along the grain boundaries and inside.With the addition of 0.5 wt.%Gd,the secondary phase become granular,and the I phase and W phase was formed.With the content of Gd was changed from 1 wt.%to 2 wt.%,the morphology of secondary phase changed from granular and strip for semi continuous network,and the components were I phase and W phase.After homogenization,the secondary phase of Mg-4Zn-0.5Ca alloy was dissolved into the matrix,and the secondary phase of Mg-4Zn-0.5Ca-xGd?x=0.5,1,2?alloys was partly dissolved into the matrix,and residual secondary phase belongs to W phase.When the amount of Gd was 2 wt.%,the optimal comprehensive mechanical properties of Mg-4Zn-0.5Ca alloy were obtained.The grain size of as-extruded Mg-4Zn-2Gd-0.5Ca alloys was refined obviously and mechanical properties were significantly improved after different extrusion processes,and there were dynamic precipitates I phases.With the increase of extrusion temperature,extrusion rate and extrusion ratio,the average size and volume fraction of DRX grains and I phases increased gradually,yield strength?YS?and tensile strength?UTS?decreased gradually,elongation?EL?increased gradually.The optimal comprehensive mechanical properties was obtained at extrusion temperature of 280^oC,extrusion rate of 0.01 mm/s and extrusion ratio of 25:1,and UTS,YS and EL were 369.79 MPa,400.27 MPa and 7.83%,respectively.In addition,the grain size of Mg-4Zn-0.5Ca alloy with different Gd content were refined and mechanical properties were significantly improved after extrusion.With the increase of Gd content,the grain size and volume fraction of DRX gradually decreased,the average size and volume fraction of dynamic precipitate phase increased first and then decreased,the texture become strong,YS and UTS increased gradually,and the EL decreased gradually.The grain size of Mg-4Zn-2Gd-0.5Ca alloy was significantly refined after multidirectional forging?MDF?,and the mechanical properties were obviously improved.After three forging,the grain size of DRX was slightly grown,the volume fraction of DRX was significantly increased,the strength was not changed,the elongation increased significantly.When the forging number continued to increase to six times,the grain size and volume fraction of DRX had little change in comparison with the three forging alloy,and the strength and elongation also had little change.After extrusion,the grain size of MDF alloys was further refined,and YS,UTS and EL were significantly improved.The grain size can be obviously refined and ultrafine grains was realized after extrusion,while the volume fraction of DRX was low,which leads to the high strength and low elongation.The refinement effect of MDF on grain size was weaker than that of extrusion,but it can significantly increase the volume fraction of DRX,resulting in a significant increase in elongation,but the strength was lower.After multistep deformation?MDF+ED?,the grain size of DRX was refined and the DRX volume fraction was improved,and excellent strength and plasticity of Mg-4Zn-2Gd-0.5Ca alloy were obtained.The 3FD-ED alloy exhibited the excellent comprehensive mechanical properties,and its YS,UTE and EL were 308.84 MPa,333.51 Mpa and 32.69%,respectively.