Investigation On The Microstructure And Mechanical Properties Of TM30 Alloy Processed By ECAP

Magnesium(Mg)and its alloys are potential materials in industry application.Their applications in processing are restricted by poor plasticity,severe plastic deformation is taken to improve their mechanical properties and processability.In this paper,equal channel angular pressing(ECAP)was processed on the as-extruded Mg-3Sn-0.5Mn(TM30)bars.Samples were ECAPed at 320℃to 4 passes(4P)through B_C route,and samples were ECAPed at 250℃to 8P through B_C route after annealing.Optical Microscope(OM),Scanning Electron Microscope(SEM),Electron Backscatter Diffraction(EBSD),Transmission Electron Microscope(TEM)and X-ray Diffraction(XRD)were used to analyze microstructure,precipitate phase and texture of TM30 alloy after ECAP at different temperature.Microhardness test and tensile test were applied to investigate mechanical properties of TM30 alloy after ECAP at different temperature.The influence of microstructure evolution on mechanical properties was investigated.Besides,plastic deformation mechanism of TM30 alloy after ECAP was studied.The microstructure evolution characteristic of TM30 alloy after ECAP 4P at 250℃was:average grain size of TM30 alloy was refined from 11.11μm before ECAP to 1.90μm after 4P,homogeneous equiaxed grains were obtained after 4P;average precipitate phase size increased from 1.00μm before ECAP to 1.13μm after 4P,morphology of precipitate phase changed from block shape to elliptical shape;textural orientation rotated to approximately 56°from transversal direction(TD)toward extrusion direction(ED)with strengthened extreme density.The mechanical properties of TM30 alloy after ECAP at 250℃were:after ECAP 1P,yield strength of TM30 alloy was 97.2MPa(compared to 219.3MPa before ECAP),ultimate tensile strength of TM30 alloy was 227.7MPa(compared to 257.8MPa before ECAP),fraction elongation of TM30 alloy reached to 28.3%;microhardness of TM30 alloy was 54.81Hv after ECAP 2P which increased 17.2%compared with that before ECAP;after ECAP 4P,yield strength of TM30 alloy increased to 125.6MPa,ultimate tensile strength of TM30 alloy reduced to 205.1MPa,fracture elongation of TM30 alloy increased 47.2%to 37.1%compared with situation before ECAP;microhardness of TM30 alloy was 46.49Hv after ECAP 8P.The microstructure evolution characteristic of TM30 alloy after ECAP 4P at 320℃was:average grain size of TM30 alloy was refined from 12.86μm before ECAP to 1.65μm after 4P,homogeneous equiaxed grains were obtained after 4P;average precipitate phase size increased with increasing pass number(from 0.79μm before ECAP to 1.01μm after ECAP 4P),morphology of precipitate phase changed from block shape to elliptical shape and precipitate phase segregated along grain boundaries;textural orientation rotated to approximately 8°from TD toward normal direction(ND)with strengthened extreme density,texture were consisted of deformed texture and recrystallized texture.The mechanical properties of TM30 alloy after ECAP at 320℃were:after ECAP 1P,microhardness of TM30 alloy was 56.19Hv which increased 26.0%compared with that before ECAP,yield strength of TM30 alloy was 109.5MPa,ultimate tensile strength of TM30 alloy was 256.3MPa,fraction elongation of TM30 alloy reached to 25.1%;after ECAP 4P,yield strength of TM30 alloy increased to 153.8MPa,ultimate tensile strength of TM30 alloy reduced to 195.6MPa,fracture elongation of TM30alloy increased 164%to 58.6%compared with situation before ECAP.Yield strength of TM30 alloy decreased after ECAP 1P,then increased with increasing pass number,ultimate tensile strength of TM30 alloy decreased with increasing pass number,but fracture elongation of TM30 alloy increased significantly with increasing pass number.Mechanical properties’changes were decided by combined effect of grain refinement strength,dislocation density,texture weaken and activation of non-basal slip.After ECAP 1P,due to textural orientation rotation caused by shear stress during ECAP processing,the k in Hall-Petch relationship was reduced,yield strength decreased dramatically.Differences of microstructure evolution and mechanical properties’change of TM30 alloy after ECAP at different temperatures were caused by dynamic recrystallization(DRX),grain refinement mechanism of TM30 alloy during ECAP processing at 250℃was dominated by deformation induction,also DRX play a role on the grain refinement of TM30 alloy at 320℃ECAP.Plastic deformation of TM30 alloy during ECAP processing was dominated by(0001)basal slip,at the beginning of plastic deformation,tensile twinning was activated to coordinate structure deformation,at subsequent passes,non-basal slip was activated,plastic deformability of TM30 alloy was improved.