Local hardening and asymmetric twin growth by twin-twin interactions in a Mg alloy

In this study, the role of twin-twin interactions on the distributions of local defects (e.g., dislocations) and stress fields in a magnesium alloy is investigated. A co-zone ( 10 1 over bar 2 ) -( 1 over bar 012 ) tensile twin junction in a deformed Mg-3wt.%Y alloy is analyzed using transmission electron microscopy (TEM). The results show that the morphology of the impinging ( 1 over bar 012 ) twin is asymmetric, and the non-interacting boundary of the recipient ( 10 1 over bar 2 ) twin is irregular. Detailed analysis of TEM images reveals that type-II pyramidal [ 1 over bar 2 1 over bar 3 ]( 1 2 over bar 12 ) dislocations concentrate in the vicinity of the twin-twin junction site. The same ( c + a dislocations are also observed inside the interacting twin domains along with a few (a dislocations. The ( c + a dislocations emanating from the impinging ( 1 over bar 012 ) twin boundary have edge character and are extended with faults parallel to the basal plane. In contrast, the ( c + a dislocations connected to the recipient ( 10 1 over bar 2 ) twin are predominantly screw orientation and compact. Elasto-viscoplastic fast Fourier transform based crystal plasticity calculations are performed to rationalize the observed twin morphology and local dislocation distribution. The model calculations suggest that the local stress fields generated at the junction site where the two twins meet are responsible for the experimentally observed concentration of ( c + a dislocations. The calculated stress fields are asymmetric with respect to the junction site, explaining the observed asymmetric morphology of the impinging twin. Overall, these findings show strong effects of twin-twin interactions on the distribution of dislocations as well as the evolution of the twinned microstructure and as such, can help advance understanding of twinning in Mg alloys and their effect on mechanical behavior.(c) 2022 Chongqing University. Publishing services provided by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ) Peer review under responsibility of Chongqing University

Automated summary

This study investigates the effects of twin-twin interactions on the distribution of defects and stress fields in a magnesium alloy. The analysis focuses on a specific twin junction in a deformed Mg-3wt.%Y alloy. The results show that the morphology of the twins is asymmetric and the dislocations concentrate near the twin-twin junction site. Crystal plasticity calculations suggest that the local stress fields generated at the junction site are responsible for the observed concentration of dislocations. These findings provide insights into the twinning behavior and mechanical properties of Mg alloys.