Yield point elongation due to twinning in a magnesium alloy

By Matthew Barnett, M. Nave, A. Ghaderi. 2012

304 citations recorded by the source corpus.

Abstract Fine-grained magnesium alloy AZ31 displays a yield elongation when deformed such that yielding occurs by twinning. That is, following yielding there is a plateau in the stress–strain curve. The present paper presents a microstructural analysis of the twins in deformed samples. A major aim is to explain the yield elongation and in particular why it decreases and eventually disappears with increasing grain size. It is shown that during the Luders yield elongation twins initiate twinning events in neighbouring grains and in this manner twinning spreads its way progressively over the sample. This occurs at a twinning frequency of approximately one twin per grain. A criterion for the presence of a Luders strain is developed based on twin transfer across boundaries. It is shown that higher Luders strains and stresses are expected for finer grain sizes. The key to understanding the effect is that it arises from the condition for Luders band propagation whereby the twins on the Luders band front must stimulate, on average, one twin each within the fresh material ahead of the front, at a constant value of applied stress. An important part of the derivation followed here is that at the higher stresses seen in fine-grained samples, the twin aspect ratio is larger and consequently the strain at the grain level corresponding to a single twinning event is higher in finer-grained samples.

Subfields: Biomaterials, Materials Chemistry, Mechanical Engineering

View Paper: https://www.semanticscholar.org/paper/affad0a5f4e27c5b1a5deca55c2c1d4e160ec40f

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Citations in the corpus

Modeling twinning and detwinning behavior of Mg alloy ZK60A during monotonic and cyclic loading (2015, background): “, 2010b; Barnett et al., 2012). While the phenomenological models often capture this sharp yielding behavior, most crystal plasticity models fail to capture sharp initial yielding phenomenon. Additionally, even when initial yielding by twinning is experimentally observed to be abrupt, the reverse-yi”
Grain boundaries and interfaces in slip transfer (2014, unknown): “Such e ﬀ ects are much more commonly observed in magnesium alloys [65–67].”