<i>In-Situ</i> Evaluation of Detwinning Behavior in Extruded AZ31 Mg Alloy by AE

Abstract

Tension twinning readily occurs under compressive loading along extrusion direction because extruded AZ31 Mg plate has the texture with the basal planes parallel to the extrusion direction. Detwinning occurs in the twinned areas during tensile loading in the opposite direction. In this study, acoustic emission (AE) during the tensile test was investigated for the evaluation of detwinning behavior. Different AE features depending on the strain level were observed and detwinning behavior was divided into three stages. In the first stage, many AE signals with higher peak frequency were generated, then very few AE signals were observed in the second stage, and finally again some AE signals with lower peak frequency were observed in the third stage. In addition, EBSD analysis was conducted to identify phenomena in each stage. The results suggested that twin boundary starts to move in the first stage, then twin area shrinks in the second stage, and twin area disappears in the third stage. Deference of AE characteristics in each stage seems to be caused by these phenomena. It can be concluded that AE is an effective method for evaluation of detwinning behavior.

Detwining in Mg alloy with a high density of twin boundaries

“…Partial detwinning is observed clearly at this strain level. In contrast to the detwinning induced by reverse loading, which left residual lenticular twins without twinning traces, as observed by Caceres et al [6] and Yasutomi and Enoki [21], the detwinning behaves very inhomogeneously under the present conditions and seems to initiate not from the tips but in the interiors of preexisting twins. Therefore, the residual twins observed in the present research are much more irregular; distinct twin boundary traces are observed after detwinning, as indicated by the white lines in the IPF map (figure 9(a)) and the contrast in the IQ map (figure 9(b)).…”

“…During the subsequent compression along the ED, there are two possible twinning variants for detwinning: reorientation of the c -axis forward by another 87° following (2) * (3), which is the same twinning variant that occurs during radial compression, and reorientation in the reverse direction to the original position following (2) * (1). Detwinning through the (2) * (1) route will give rise to a complete disappearance of the twin boundary or no twinning trace, like that during reverse loading [21, 25]. In contrast, detwinning through the (2) * (3) route actually proceeds through {10-12}-{10-12} re-twinning which will be accompanied by a transition of the twin boundaries (87°) into LABs with misorientation angles of about 6° (figure 8).…”

Deformation mechanisms underlying tension–compression asymmetry in magnesium alloy ZK60 revealed by acoustic emission monitoring

“…Observations of AE associated with de-twinning in a strongly textured commercial purity Mg were reported recently by Enoki and co-authors [43,44]. In this context, the specific features of AE response in the CTC loading path to the first reversal from compression to tension are of interest.…”

Effect of tensile strain rates on flow stress for extruded AZ31 and AZ61 magnesium alloys

“…Twinning provides a high dislocation slip by producing more barriers between grains [22]. Moreover, Koike et al [23], Barnett [24,25] and Yasutomi and Enoki [26] argued that twinning formation results in extruded materials from the extrusion process. Figure 8 shows the effect of strain rate on elongations of extruded AZ31 and AZ61 magnesium alloys.…”