Study On Dynamic Compression Deformation Behavior Of As-extruded Mg-6Zn-1Cu-xY-0.6Zr Alloys

Magnesium alloy has the advantages of high specific strength,damping and shock absorption.In practical engineering applications,the mechanical properties and microstructure changes of magnesium alloys under dynamic and quasi-static loading conditions are obvious differences.In this study,the as-extrusion Mg-6Zn-1Cu-xY-0.6Zr（x=0,1,2,3）alloys was obtained by using extrusion-shear process which integrated direct extrusion with equal channel angular pressing.Through the change of Y content,adjusted the amount and type of second phase and refined grain in Mg-6Zn-1Cu-xY-0.6Zr（x=0,1,2,3）alloys,the mechanical properties and anisotropy of investigated alloys were improved.Furthermore,the test of dynamic compression along extrusion direction（ED）and extrusion radius direction（RD）at strain rates of 1100 s^-1～2200 s^-1 was studied by Split Hopkinson Pressure Bar（SHPB）.The microstructure evolution and fracture behavior of as-extrusion Mg-6Zn-1Cu-xY-0.6Zr（x=0,1,2,3）alloys were investigated by Optical Microscopy（OM）,Scanning Electron Microscopy（SEM）,X-ray Diffraction Analysis（XRD）,Electron Back-Scattered Diffraction（EBSD）and Transmission Electron Microscopy（TEM）.In addition,the evolution of fracture behavior,deformation mechanism and anisotropy after dynamic compression were analyzed.The results show that as-extruded Mg-6Zn-1Cu-xY-0.6Zr（x=1,2,3）alloys are mainly consisted ofα-Mg matrix,MgZnCu phase,Mg₃YZn₆（I phase）and（W phase）.Meanwhile,the amount of second phase increases,the average grain sizes decrease from 7.2μm to 1.3μm and the density of（0002）textures decrease from 9.95 to 6.80 with increasing Y content.When the four alloys are dynamically compressed along ED and RD,the yield strength and fracture strength are improved with the increase of Y content.Meanwhile,the fracture mechanisms of alloys transfers from brittle fracture and local melting to ductile fracture due to the increment of energy density and insulation temperature by the addition of Y content.The results show that the main deformation modes of the four alloys under dynamic compression along ED are extension twinning and base and non-base slip.Due to the extension twinning initiated and propagated,the texture transform from<0-110>to<0002>,that is,（0002）the texture changes from parallel to ED to perpendicular to ED.While,the base and non-base slip and few extension twinning are dominant under dynamic compression along RD,and the c-axes of the crystals is mainly parallel to RD,that is,the texture of（0002）is perpendicular to RD.