Influence of grain size and grain boundary misorientation on the fatigue crack initiation mechanisms of textured AZ31 Mg alloy

The deformation and crack initiation mechanisms were analyzed in a textured AZ31B-O Mg alloy subjected to fully-reversed, strain-controlled cyclic deformation along the rolling direction after 50 cycles (approximately 33% of the fatigue life). Distinct deformation bands corresponding to pyramidal slip or tensile twins were found in 538 grains out of 2100 grains. Slip trace analysis showed that 72.3% were pyramidal slip bands and 18.4% were twin boundaries. Both pyramidal slip and twinning was only found in 9.1% of the grains with deformation bands. Cracking was widespread after 50 cycles. Grain boundary cracks were found in approximate to 15% of the small grains (< 20 mu m) and they were mainly associated with high angle grain boundaries (>40 degrees). Cracking was also found to occur by transgranular cracks parallel to the pyramidal slip bands or twin boundaries in large grains (>45 mu m). The majority (>60%) of these large grains presented transgranular cracks after 50 cycles. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Automated summary

The analysis of a textured AZ31B-O Mg alloy subjected to fully-reversed, strain-controlled cyclic deformation revealed that pyramidal slip and twinning coexisted in only 9.1% of the grains after 50 cycles, while cracking was widespread, with grain boundary cracks found in approximately 15% of small grains and transgranular cracks in large grains after 50 cycles.