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Metallurgical and Materials Transactions A

, Volume 45, Issue 8, pp 3292–3307 | Cite as

Effect of Stress Triaxiality on the Flow and Fracture of Mg Alloy AZ31

  • Babak Kondori
  • A. Amine BenzergaEmail author
Article

Abstract

The microscopic damage mechanisms operating in a hot-rolled magnesium alloy AZ31B are investigated under both uniaxial and controlled triaxial loadings. Their connection to macroscopic fracture strains and fracture mode (normal vs shear) is elucidated using postmortem fractography, interrupted tests, and microscopic analysis. The fracture locus (strain-to-failure vs stress triaxiality) exhibits a maximum at moderate triaxiality, and the strain-to-failure is found to be greater in notched specimens than in initially smooth ones. A transition from twinning-induced fracture under uniaxial loading to microvoid coalescence fracture under triaxial loading is evidenced. It is argued that this transition accounts in part for the observed greater ductility in notched bars. The evolution of plastic anisotropy with stress triaxiality is also investigated. It is inferred that anisotropic plasticity at a macroscopic scale suffices to account for the observed transition in the fracture mode from flat (triaxial loading) to shear-like (uniaxial loading). Damage is found to initiate at second-phase particles and deformation twins. Fracture surfaces of broken specimens exhibit granular morphology, coarse splits, twin-sized crack traces, as well as shallow and deep dimples, in proportions that depend on the overall stress triaxiality and fracture mode. An important finding is that AZ31B has a greater tolerance to ductile damage accumulation than has been believed thus far, based on the fracture behavior in uniaxial specimens. Another finding, common to both tension and compression, is the increase in volumetric strain, the microscopic origins of which remain to be elucidated.

Keywords

Crack Initiation Shear Failure Stress Triaxiality Uniaxial Loading Anisotropy Ratio 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Notes

Acknowledgments

This research was supported by the NPRP Grant No 4-1411-2-555 from the Qatar National Research Fund (a member of Qatar Foundation). The statements made herein are solely the responsibility of the authors.

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Copyright information

© The Minerals, Metals & Materials Society and ASM International 2014

Authors and Affiliations

  1. 1.Department of Materials Science and EngineeringTexas A&M UniversityCollege StationUSA
  2. 2.Department of Aerospace EngineeringTexas A&M UniversityCollege StationUSA

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