Abstract
Friction stir welding (FSW) has promising application potential in Mg alloys. However, the texture distribution in stir zone (SZ) is usually complicated for Mg alloys, which deterioriates the joint performance. In this study, the texture distribution in SZ was tailored by applying two kinds of post-weld compression deformation along normal direction (ND) or welding direction (WD) of the FSWed AZ31 Mg alloy plates. The twinning behavior and texture change in the various regions of SZ were then evaluated by electron back scatter diffraction (EBSD) characterization. The effect of texture change on the joint performance was discussed in terms of Schmid factors (SFs) for basal slip and extension twinning. The results showed that profuse extension twins were formed through the whole SZ for the sample subjected to compression along ND, whereas they were observed mainly in SZ-side for the sample compressed along WD. Most of the twins were present in the forms of twin bands or chains. The directions of the twin bands or chains were related to the habit plane traces of selected twin variants. The ND post-weld compression had better strengthening effects on the joints compared to the WD compression, and the underline mechanism was discussed.
Highlights
Friction stir welding (FSW) has promising application potential in Mg alloys
The results show that variants V1 and V2 have the best activation preference in NDCP4 sample, while variants V3 and V4 do in WDCP4 sample
The microstructure and texture changes during post-welding compressin were comparatively studied between two different strain paths, i.e., compression along normal direction (ND) and welding direction (WD)
Summary
Friction stir welding (FSW) has promising application potential in Mg alloys. the texture distribution in stir zone (SZ) is usually complicated for Mg alloys, which deterioriates the joint performance. Recent studies indicated that the FSW texture in Mg alloys could be re-distributed by applying post-weld plastic deformation[20,35,36]. Such a strengthening strategy has been widely investigated on Mg alloys in the form of rolling sheets or extrusion rods[37,38]. The effects of twinning deformation on texture variation and strength enhancement have been reported in FSW joints of AZ31 Mg alloys[35,36] The twinning deformation they applied includes post-welding rolling and tensile deformation. The general features of twin lamellae in the two compression processes and their strengthening mechanisms on Mg FSW joints were obtained
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