Effects Of Hot Compression On The Mechanical Properties And Creep Resistance Of Magnesium Alloy Extruded Rods

Magnesium(Mg)alloys have the advantages of low density and high specific strength,which are believed as light structural materials with broad application prospects.The extrusion process can significantly improve the mechanical properties of Mg alloys,which has attracted extra attention.In this paper,the objects were Mg-9.3Gd-2.6Y-0.5Zr,Mg-5.5Gd-4.4Y-1.1Zn-0.5Zr and Mg-1.0Zn-0.9Mn extruded rods,and the effects of hot compression on their mechanical properties and creep resistance were investigated.Microstrcture evlotioins,texture changes and dislocation movements during hot compression and creep were observed.The fracture and creep mechanisms of different samples were summarized.For Mg-5.5Gd-4.4Y-1.1Zn-0.5Zr extruded rods,hot compression could improve fracture toughness and tansform the crack propagation mode from transgranular to intergranular during the three-point bending tests.During creep,β’ phases would precipitate and the precipitation free zones(PFZs)appeared at the grain boundaries.The creep mechanism of the A-NHC sample without hot compression was <a> dislocation rings around β’ phases,the creep bahavior of the A-EDHC sample with hot compression along ED were dominated by grain boundary slip and pyramidal <c+a> slip,the creep mechanism of the A-TDHC sample with hot compression along TD were grain boundary slip,pyramidal <c+a>slip and stacking faults(SFs).The order of creep resistance of the three samples was: A-NHC > A-TDHC > A-EDHC.The worst the creep resistance of the A-EDHC can be attributed to the irregular PFZs and grain boundary slip.For Mg-5.5Gd-4.4Y-1.1Zn-0.5Zr extruded rods,RE-rich particles and Zn-Zr compounds precipitated and the transformation from 18 R to14H LPSO phases happened during heat treatment.What’s more,more18 R LPSO phases would be transformed into 14 H LPSO phases,and these high-density lamellar 14 H LPSO phases would be kinked to adapt to plastic deformation during hot compression.The kinked bands(KBs)and the lamellar LPSO phases perpendicular to the loading direction or at a large angle could hinder the crack propagation and improve the fracture toughness.The creep mechanism of the B-NHC sample without hot compression was base slip,while the creep bahaviors of the B-EDHC with hot compression along ED and B-TDHC sample with hot compression along TD were dominated by pyramidal <c+a> slip and grain boundary slip.The order of creep resistance of the three samples was: B-NHC > B-TDHC > B-EDHC.Grain boundary slip and the defects formed at the grain boundaries and the tip of the KBs during hot compression would deteriorate the creep resistance of the latter two samples.The room temperature strength and plasticity of Mg-1.0Zn-0.9Mn extruded rods were improved simultaneously by hot compression along TD,the effect of which became better with the increase of deformation.The creep mechanism of the C-NHC sample without hot compression was diffusion mechanism and grain boundary slip,while the creep bahaviors of the C-TD05 with hot compression along TD(ε = 0.5)and CTD10 with hot compression along TD(ε = 1.0)samples were controlled by viscous gliding and grain boundary slip.The order of creep resistance of the three samples was: C-NHC > C-TD05 > C-TD10.The strong grain boundary slip would seriously damage their creep resistance.