Slip mode dependency of dislocation shearing and looping of precipitates in Mg alloy WE43

The effect of precipitates on the strength of Mg alloy, WE43, has been investigated. Transmission electron microscopy (TEM) provides unequivocal evidence that the ordered prismatic plate-shaped β′ precipitates are sheared by basal slip of dislocations. However, non-basal and pyramidal dislocations are unable to shear the precipitates, and instead bow around them during plastic deformation. In the latter case the Orowan looping model accurately predicts precipitate hardening. For the case of the shearable particles, it is proposed that order strengthening is the dominant mechanism by which the β′ phase provides strengthening to the basal slip system, and a new model quantifying this effect is developed. Using this model in conjunction with TEM observations and elastoplastic self-consistent polycrystal modeling, the anti-phase boundary energy (APB) of the precipitates is estimated to be 210 mJ/m2. The present work has significant implications for Mg alloy design strategies, and emphasizes the importance of considering both precipitate shearing and Orowan looping of precipitates. Finally, it suggests the value of making first-principles predictions of APB energies (γ-surfaces) of the candidate strengthening phases.