Discontinuous and inhomogeneous strain distributions under monotonic and cyclic loading in textured wrought magnesium alloys

Abstract

The present work investigates the deformation behaviour of strongly textured AZ31B wrought magnesium sheets under monotonic as well as cyclic mechanical loading. Of special focus is the distribution of strain, which is investigated employing optical strain field measurements on the specimen surfaces. Microstructural investigations of the material after loading provide detailed information on the underlying deformation characteristics. The investigations show that bands of twinned grains (BTGs) form up once twinning occurs. These BTGs consist of solely {101‾2} tension twins and are clearly delimited to the adjacent absolutely twin-free regions. Most importantly, strain fields are strongly inhomogeneous and discontinuous due to these BTGs with considerably higher compressive strain inside BTGs, both after monotonic and cyclic loading. During the first few load cycles, BTGs are observed to grow and the formation of new BTGs can occur. Additionally, a significant hardening is found during the first load cycles, most likely caused by residual twins and unretwinnable twins. However, material behaviour stabilizes after a few load cycles and remains approximately constant for most of a specimen's lifetime. The presented specific deformation characteristics are important for understanding and describing the material. Modelling the investigated material behaviour is not yet completely feasible with phenomenological constitutive models, which is why important modelling aspects are discussed.