The roles of stress state and pre-straining on Swift effect for an extruded AZ31 Mg alloy

The Swift effect of Mg alloy is sensitive to initial texture.However,dislocation slip is the main deformation mechanism during torsion of Mg alloy.The underlying relation of Swift effect and dislocation slip is still not clarified.The effect of stress state and pre-straining on Swift effect was studied experimentally during free-end torsion for an extruded AZ31 alloy.The free-end torsion was performed with axial tension and compression stress which is lower than yield stress.It is found that the transition of axial deformation from contraction to elongation occurs when the axial stress changes from negative to positive.The pre-dislocations introduced by pre-tension promote axial shortening during torsion.While the pre-twins introduced by pre-compression are inhibition of axial shortening.The change of axial deformation is attributed to competition between twinning and prismatic slip.The axial shortening of extruded Mg alloy is generated by tensile twinning leading to c-axis strain.In contrast,the axial elongation can be generated by the activation of prismatic slip.The magnitude of axial strain generated by twinning is larger than that by prismatic slip.Moreover,the occurrence of detwinning results in axial elongation at low shear strain.

Anisotropy of wrought magnesium alloys: A focused overview

In this paper, the relationship between anisotropic mechanical properties and the corresponding microstructure evolution of wrought magnesium alloys is critically reviewed. Experimental observations of the strong anisotropy(including the strength differential effect) induced by texture and twinning are discussed under different loading conditions(i.e., monotonic, cyclic and multiaxial loading). An accurate constitutive model is essential to describe the mechanical responses and to predict the forming performance considering engineering applications. Therefore, macroscale constitutive modeling of the anisotropy of magnesium alloys with directional distortional hardening are comprehensively reviewed with different approaches. To clarify the origin of the anisotropic behavior, physics-based mesoscale modeling of the anisotropy is also compared in detail.

Effect of axial preloading on mechanical behavior during the free-end torsion of an extruded AZ31 magnesium alloy

Large plastic deformation commonly occurs during the practical forming process in industries.Compared with uniaxial tension/compression,torsion is a more effective approach to investigate mechanical behavior under large deformation.The response of the large strain torsion of magnesium alloy is sensitive to the initial texture and twinning.Therefore,an extruded AZ31 alloy was pre-stressed in tension and compression to introduce dislocations and twins in the current work.Subsequently,torsion tests were conducted to clarify the effects of twinning and dislocation on subsequent deformation responses.The corresponding microstructure and deformation mechanisms were explored on the basis of viscoplastic self-consistent(VPSC)modeling.The experimental observations on stress-strain responses and pole figures were captured by simulation work.It was found that twins make less contribution to plastic deformation,which results in small change in texture direction under pure torsion and torsion after pretension.The activity of the slip/twin system and the mechanical properties are affected by different initial textures and active conditions of the system.Moreover,the stress state during combined tension-torsion loading benefits the reduction of texture intensity.