Strain-Rate Sensitivity Enhanced by Grain-Boundary Sliding in Creep Condition for AZ31 Magnesium Alloy at Room Temperature

Abstract:

This study investigated strain-rate sensitivity (SRS) in an as-extruded AZ31 magnesium (Mg) alloy with grain size of about 10 mm. Although the alloy shows negligible SRS at strain rates of >10^-5 s^-1 at room temperature, the exponent increased by one order from 0.008 to 0.06 with decrease of the strain rate down to 10^-8 s^-1. The activation volume (V) was evaluated as approximately 100b³ at high strain rates and as about 15b³ at low strain rates (where b is the Burgers vector). In addition, deformation twin was observed only at high strain rates. Because the twin nucleates at the grain boundary, stress concentration is necessary to be accommodated by dislocation absorption into the grain boundary at low strain rates. Extrinsic grain boundary dislocations move and engender grain boundary sliding (GBS) with low thermal assistance. Therefore, GBS enhances and engenders SRS in AZ31 Mg alloy at room temperature.

• Periodical: Materials Science Forum (Volumes 838-839)
• Pages: 106-109
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.838-839.106
• Online since: January 2016
• Authors: Tetsuya Matsunaga*, Hidetoshi Somekawa, Hiromichi Hongo, Masaaki Tabuchi
• Keywords: AZ31 Mg Alloy, Grain Boundary, Low Thermally Activated Process, Strain-Rate Sensitivity

References

[1] M.A. Kumar, A.K. Kanjarla, S.R. Niezgoda, R.A. Lebensohn, C.N. Tome, Numerical study of the stress state of a deformation twin in magnesium, Acta Mater. 84 (2015) 349-358.

DOI: 10.1016/j.actamat.2014.10.048

[2] R. Korla, A.H. Chokshi, Strain-rate sensitivity and microstructural evolution in a Mg–Al–Zn alloy, Scr. Mater. 63 (2010) 913-916.

DOI: 10.1016/j.scriptamat.2010.06.047

[3] H. Conrad, L. Hays, G. Schoeck, H. Wiedersich, On the rate-controlling mechanism for plastic flow of Mg crystals at low temperatures, Acta Metall. 9 (1961) 367-378.

DOI: 10.1016/0001-6160(61)90230-9

[4] A.G. Evans, R.D. Rawlings, The thermally activated deformation of crystalline materials, phys. stat. sol. 34 (1969) 9-31.

DOI: 10.1002/pssb.19690340102

[5] H. Somekawa, K. Hirai, H. Watanabe, Y. Takigawa, K. Higashi, Dislocation creep behavior in Mg–Al–Zn alloys, Mater. Sci. Eng. A. 407 (2005) 53-61.

DOI: 10.1016/j.msea.2005.06.059

[6] H. Conrad, S. Frederick, The effect of temperature and strain rate on the flow stress of iron, Acta Metall. 10 (1962) 1013-1020.

DOI: 10.1016/0001-6160(62)90070-6

[7] R.J. Arsenault, The double-kink model for low-temperature deformation of B.C.C. metals and solid solutions, Acta Metall. 15 (1967) 501-511.

DOI: 10.1016/0001-6160(67)90083-1

[8] A. Segger, On the theory of the low-temperature internal friction peak observed in metals, Phil. Mag. 1 (1956) 651-662.

[9] T. Neeraj, D. -H. Hou, G.S. Daehn, M.J. Mills, Phenomenological and microstructural analysis of room temperature creep in titanium alloys, Acta Mater. 48 (2000) 1225-1238.

DOI: 10.1016/s1359-6454(99)00426-7

[10] T. Matsunaga, T. Kameyama, K. Takahashi, E. Sato, Intragranular deformation mechanisms during ambient-temperature creep in hexagonal close-packed metals, Trans. JIM. 50 (2009) 2865-2872.

DOI: 10.2320/matertrans.m2009224

[11] T. Matsunaga, H. Somekawa, H. Hongo, M. Tabuchi, Submitted.

[12] P.D. Wu, X.Q. Guo, H. Qiao, D.J. Lloyd, A constitutive model of twin nucleation, propagation and growth in magnesium crystal, Mater. Sci. Eng. A. 625 (2015) 140-145.

DOI: 10.1016/j.msea.2014.11.096

[13] R.Z. Valiev, O.A. Kaibyshev, Mechanism of Superplastic Deformation in a Mgnesium Alloy II. The Role of Grain Boundaries, phys. stat. sol. (a). 44 (1977) 477-484.

DOI: 10.1002/pssa.2210440209

[14] J. Koike, R. Ohyama, T. Kobayashi, M. Suzuki, K. Maruyama, Grain-boundary sliding in AZ31 magnesium alloys at room temperature to 523 K, Mater. Trans. 44 (2003) 445-451.

DOI: 10.2320/matertrans.44.445

[15] T. Matsunaga, E. Sato, Estimation of Grain Boundary Sliding During Ambient-Temperature Creep in Hexagonal Close-Packed Metals Using Atomic Force Microscope, in: V. Nalladega (Eds. ), Scanning Probe Microscopy-Physical Property Characterization at Nanoscale, InTech, Croatia, 2012, pp.203-214.

DOI: 10.5772/35640