Effect of textural variation and twinning activity on fracture behavior of friction stir welded AZ31 Mg alloy in bending tests

Strong local texture is usually formed in friction stir welded (FSW) Mg alloys and varies in different positions of the weld zone. Textural variation has an impact on fracture behavior and caused a poor mechanical property during the transverse tensile tests. However, due to the different stress and strain state between the inner and outer surfaces, the effect of textural variation on fracture behavior in bending tests is still unknown. The present study aims to investigate the relationship between textural variation, twinning activity and fracture behaviors in bending tests by Schmid factor analysis. It is found that sudden change of texture at the transition zone (TZ)/stir zone (SZ) interface and different twinning activity between the TZ and SZ-side have an impact on fracture behavior of bending samples, especially for crack propagation at the TZ/SZ interface for Surface bending test. The effect of textural variation on fracture behavior in bending is highly dependent on the local stress state and it can be well explained by the calculated Schmid factor in terms of the assumed stress state for bending. The present work is helpful for tailoring the local texture to change fracture behavior and improve the joint strength of FSW Mg welds.