The Effects of Basal and Prismatic Precipitates on Deformation Twinning in AZ91 Magnesium Alloy

The advancement of Mg-based applications is motivated by inherently the high specific-strength and low densities of Mg and its alloys. The AZ91 alloy is one such exemplary cast Mg alloy that is being considered due to its relatively high strength, excellent corrosion resistance and castability. However, like most Mg alloys, it is not yet widely used due to poor formability and a complex, anisotropic plastic response. These behaviors have been linked to their propensity to deform by twinning, in addition to slip. Furthermore, the grains in the AZ91 alloy contain β-phase precipitates, which are similar in size as the twin lamellae. In this study, we use an elasto-viscoplastic fast-Fourier-transform (EVP-FFT) crystal plasticity micromechanics model to examine the interactions between \(\left\{ {10\overline{1}2} \right\}\)-type extension twins and two types of precipitates—basal and prismatic precipitates. The calculations focus on conditions that determine whether the twin is blocked by the precipitate or can cross the precipitate by nucleating a new twin on the other side of it. The effects of twin thickness, relative to the size of the precipitate, and precipitate types are investigated. The analysis shows that both precipitates are effective at blocking the propagation of twins and limit their ability to thicken. The basal precipitates are, however, substantially easier to cross by the twin than prismatic precipitates. Furthermore, the thicker the twin is when it impinges on the precipitate, the higher the chance it can cross.