Multiscale & in-situ forming analysis of AZ31 magnesium alloy under different strain paths

2018
Alkan, Kıvanç
Formability of AZ31 Magnesium alloy is limited and strain path dependent below 180 ᵒC. In this thesis, formability behavior and fracture mechanisms of AZ31 Magnesium alloy are investigated by in-plane biaxial testing. In-situ and multiscale strain analysis reveal the microstructural features and deformation mechanisms responsible form the unusual forming behavior of the AZ31 alloy and offer possible solutions to control the forming defects and instabilities. The strain measurements show that the equivalent fracture strains of both uniaxial and equibiaxial stress states are nearly the same, however heterogeneous deformation is observed at both loading conditions. At microscale, localization ratio (Ԑlocalized/Ԑmean) is 3 in uniaxial tension and 20 in equibiaxial stretching. The localizations at the microscale reveal themselves at the macroscale and limit the formability, especially under equibiaxial stretching, by early plastic instabilities. Twinning and grain boundary slip are the main deformation mechanisms responsible for the localizations at both conditions. A detailed analysis of the microstructure by EBSD indicates that the slip activity decreases from uniaxial tension to equibiaxial stretching, while the formation of {101 ̅2}〈101 ̅1〉 tension twins dominates the deformation. In uniaxial tension, intergranular fracture occurs due to the slip assisted grain boundary sliding but in equibiaxial stretching, a mixture of a transgranular and intergranular fracture leads to the ultimate failure of the samples. Therefore, twinning activity and grain boundary slip should be suppressed to increase the formability. A uniform distribution of slip within the grains should yield the optimum formability for AZ31 Magnesium alloy.

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Citation Formats
K. Alkan, “Multiscale & in-situ forming analysis of AZ31 magnesium alloy under different strain paths,” M.S. - Master of Science, Middle East Technical University, 2018.