Room Temperature Ductility and Microstructure of Magnesium AZ31B Sheet

Formability of wrought magnesium alloys at room temperature or slightly elevated temperatures is modest, reaching about 20% elongation in a tension test and exhibiting poor resistance to strain localization and failure. The hexagonal close packed structure of Mg has few active slip systems at lower forming temperatures, limiting ductility and reducing applications in auto body structures. Much greater levels of ductility can be reached at higher temperatures (typically >300 °C), but this is expensive and inconvenient for a high-volume production environment. Tension testing and biaxial forming of annealed AZ31B magnesium alloy sheets were done at room temperature to various levels of strain. High-resolution electron back scatter diffraction (EBSD) was used to measure twin fraction and dislocation density, in order to find relationships between strain and potential failure locations within the microstructure. Twin fractions were found to have a weak positive correlation to uniaxial and biaxial tensile strain, while dislocation density was found to correlate more strongly with uniaxial tensile strain.