NUMISHEET2005 —Detroit, MI August 15-19, Cyclic and Monotonic Plasticity of Mg Sheet R. H. Wagoner, X. Lou, M. Li, S. R. Agnew*, Dept. Materials Science and Engineering The Ohio State University *University of Virginia

Advances in Understanding Springback 2 R. H. WagonerCyclic and Monotonic Plasticity of Mg Sheet Acknowledgements

Advances in Understanding Springback 3 R. H. WagonerCyclic and Monotonic Plasticity of Mg Sheet Introduction

Advances in Understanding Springback 4 R. H. WagonerCyclic and Monotonic Plasticity of Mg Sheet Mg Sheet for Forming Applications Advantages Low density - High strength- High stiffness Challenges Room-temp. formability - Asymmetric flow behavior Opportunity Forming operation using asymmetric flow?

Advances in Understanding Springback 5 R. H. WagonerCyclic and Monotonic Plasticity of Mg Sheet Slip Deformation in Mg : No strain parallel to basal poles : Difficult to activate Basal {0001} Prismatic Pyramidal

Advances in Understanding Springback 6 R. H. WagonerCyclic and Monotonic Plasticity of Mg Sheet Tensile Twinning in Mg Matrix original c 3°42' k1k1 η1η1 k2k2 k* 2 7°24' η2η2 η*2η*2Twin 2S reoriented c TD RD ST Tension Compression Patridge, Metall. Reviews,1967

Advances in Understanding Springback 7 R. H. WagonerCyclic and Monotonic Plasticity of Mg Sheet Experiments

Advances in Understanding Springback 8 R. H. WagonerCyclic and Monotonic Plasticity of Mg Sheet Tension / Compression Test Boger et al., Int. J. Plasticity, 2005 G=36.8mm B=50.8mm W=15.2mm L>3mm Side Force

Advances in Understanding Springback 9 R. H. WagonerCyclic and Monotonic Plasticity of Mg Sheet Simple Shear Test b=3mm F L=60mm W=15mm Gracio et al. Adv. Mat. Forum, 2002

Advances in Understanding Springback 10 R. H. WagonerCyclic and Monotonic Plasticity of Mg Sheet Acoustic Emission Burst AE (  s) Continuous AE (  s) Outputs:  Cumulative Count  Time Count Rate  Strain Count Rate Threshold One AE Burst Event

Advances in Understanding Springback 11 R. H. WagonerCyclic and Monotonic Plasticity of Mg Sheet Results

Advances in Understanding Springback 12 R. H. WagonerCyclic and Monotonic Plasticity of Mg Sheet Monotonic Tension, Fracture Mg AZ31B Al 6013

Advances in Understanding Springback 13 R. H. WagonerCyclic and Monotonic Plasticity of Mg Sheet Monotonic Tension vs. Compression

Advances in Understanding Springback 14 R. H. WagonerCyclic and Monotonic Plasticity of Mg Sheet Evolution of R-Values

Advances in Understanding Springback 15 R. H. WagonerCyclic and Monotonic Plasticity of Mg Sheet Single-Cycle Tests: C-T-C vs. T-C-T

Advances in Understanding Springback 16 R. H. WagonerCyclic and Monotonic Plasticity of Mg Sheet Single-Cycle Tests: C-T-C vs. T-C-T

Advances in Understanding Springback 17 R. H. WagonerCyclic and Monotonic Plasticity of Mg Sheet Multiple Cycle Tests a) Small strain, 0.04; b) Large strain, 0.07

Advances in Understanding Springback 18 R. H. WagonerCyclic and Monotonic Plasticity of Mg Sheet Saturation with Cycling a) Small strain, 0.04; b) Large strain, 0.07

Advances in Understanding Springback 19 R. H. WagonerCyclic and Monotonic Plasticity of Mg Sheet Microstructure Evolution

Advances in Understanding Springback 20 R. H. WagonerCyclic and Monotonic Plasticity of Mg Sheet Evolution of Twinning vs. Slip 6.4% max. twin strain (single xl) 5.9% max. twin strain (basal texture)

Advances in Understanding Springback 21 R. H. WagonerCyclic and Monotonic Plasticity of Mg Sheet Texture Evolution RD TD RD TD (a) Initial (b) 0.10 RD tensile strain

Advances in Understanding Springback 22 R. H. WagonerCyclic and Monotonic Plasticity of Mg Sheet Texture Evolution RD TD RD TD (c) 0.07 RD compressive strain (d) 0.1 reverse tensile strain

Advances in Understanding Springback 23 R. H. WagonerCyclic and Monotonic Plasticity of Mg Sheet Accoustic Emission, T-C

Advances in Understanding Springback 24 R. H. WagonerCyclic and Monotonic Plasticity of Mg Sheet Accoustic Emission, C-T

Advances in Understanding Springback 25 R. H. WagonerCyclic and Monotonic Plasticity of Mg Sheet Acoustic Emission, T-C-T

Advances in Understanding Springback 26 R. H. WagonerCyclic and Monotonic Plasticity of Mg Sheet Acoustic Emission, C-T-C

Advances in Understanding Springback 27 R. H. WagonerCyclic and Monotonic Plasticity of Mg Sheet Discussion

Advances in Understanding Springback 28 R. H. WagonerCyclic and Monotonic Plasticity of Mg Sheet Deformation Mechanism Summary TD ST RD   TD RD ST -- -- TD RD ST   Tension:  Slip dominated Compression: Reverse Tension:  Twinning + Slip (inflected)  Detwinning + Slip (inflected)

Advances in Understanding Springback 29 R. H. WagonerCyclic and Monotonic Plasticity of Mg Sheet Roles of Twins on Hardness CRSS: σ twinning - σ untwinning = σ t/u Obstacles to slip: Δσ obstacle Reorientation of texture, Δσ texture = σ w/twins - σ w/o twins  Can these roles be estimated quantitatively?

Advances in Understanding Springback 30 R. H. WagonerCyclic and Monotonic Plasticity of Mg Sheet Saturated Cycle Segments: C, T

Advances in Understanding Springback 31 R. H. WagonerCyclic and Monotonic Plasticity of Mg Sheet Adjusted Stress-Strain Comparison

Advances in Understanding Springback 32 R. H. WagonerCyclic and Monotonic Plasticity of Mg Sheet Twinning Effect on Hardness States: 0.01 T – 58% twinned, deformation by untwinning and slip 0.01 C – 17% twinned, deformation by twinning and slip 0.05 T – 17% twinned, deformation by untwinning and slip 0.05 C – 58% twinned, deformation by twinning and slip  Obstacle effect of twinning is 1/3-1/4 that of texture or CRSS Equations: Solution: *Lebensohn & Tome: Acta Metall, 1993

Advances in Understanding Springback 33 R. H. WagonerCyclic and Monotonic Plasticity of Mg Sheet Twinning Effect on Hardness - corrected States: 0.01 T – 58% twinned, deformation by untwinning and slip 0.01 C – 17% twinned, deformation by twinning and slip 0.05 T – 17% twinned, deformation by untwinning and slip 0.05 C – 58% twinned, deformation by twinning and slip  Obstacle effect of twinning is 1/3-1/4 that of texture or CRSS Equations: Solution: *Lebensohn & Tome: Acta Metall, 1993

Advances in Understanding Springback 34 R. H. WagonerCyclic and Monotonic Plasticity of Mg Sheet Conclusions Burst AE is correlated with twin nucleation, not growth Strain from twinning in compression: initially 90%, dropping to 50% at a strain of AE shows a second range of intense twin nucleation at strains of ~-0.06, near the exhaustion of twinning. Brittle fracture occurs in tension and simple shear. The relative effects of twinning on flow stress have been estimated: the obstacle effect is 1/4-1/3 that of the texture effect or CRSS.

Advances in Understanding Springback 35 R. H. WagonerCyclic and Monotonic Plasticity of Mg Sheet Conclusions - corrected Burst AE is correlated with twin nucleation, not growth Strain from twinning in compression: initially 90%, dropping to 50% at a strain of AE shows a second range of intense twin nucleation at strains of ~-0.06, near the exhaustion of twinning. Brittle fracture occurs in tension and simple shear. The relative effects of twinning on flow stress have been estimated: the activation stress for twinning vs. untwinning is double that of the obstacle effect or the texture effect.