The Effect Of Different Types Of {10-12} Twin Interactions On Microstructure And Mechanical Properties In Magnesium Alloys

As the lightest structural metal material at present,magnesium alloy has a broad application prospect in electronic communication,aerospace,automobile manufacturing and other industries.However,the application of magnesium alloys is limited due to their low strength,poor plasticity and poor forming properties.Magnesium alloys have a dense hexagonal structure,at room temperature,non-basal dislocations are difficult to open due to the large critical shear stress,while {10-12} twinning is easy to open due to the smaller critical shear stress,so deformation twinning plays an important role in the plastic deformation of magnesium alloys.The {10-12} twin has six equivalent variants,and under complex stress loading conditions,different twinning processes may occur simultaneously or sequentially in different regions of the grain,where the different twin variants inevitably meet,interact with each other and influence subsequent twinning,and have important implications for the evolution of the structure and material properties.The interaction of twins is divided into co-zone and non-co-zone twin interactions,with a small misorientation(～7.4°)between the two twins for co-zone twin interactions and a large misorientation(～60°)between the two twins for non-co-zone twin interactions,resulting in different effects on the microstructure of the two types of twin interactions,leading to differences in mechanical properties and mechanical properties.Therefore,clarifying the effect of different types of {10-12} twin interactions on the subsequent microstructure can provide a theoretical basis for regulating twinning and thus improving material properties,which is of great scientific significance and valuable for practical application.In this paper,the as-rolled AZ31 magnesium alloy sheet was used as the study material.It was pre-compressed by 2% along the RD direction,and then recompressed along the RD and TD directions respectively to produce different types of {10-12}twinning variants in the material.The changes in twinning in different compression directions were then observed by metallographic microscopy and quasi-in-situ EBSD combined with molecular.And molecular dynamics was used to study evolution of the microstructure and changes of stress field after the interaction of twins.Finally,the effect of different types of twin interaction on the mechanical properties was explored through mechanical property tests.The main conclusions are as follows.(1)When the pre-compression direction is the same as the re-loading direction,the interaction type is dominated by the interaction of co-zone twin variants,and the growth of the twin area within the grain mainly relies on twin growth.Twins mergers occurs between co-zone twins,rarely nucleating new twin variants.When the pre-compression direction and the re-loading direction are different,the interaction type is mainly non-cozone twin interaction,and the original twin basically stops growing,and the growth of twin area mainly relies on the nucleation and growth of new twins.(2)After co-zone twin interaction,the twin-twin interface(TTB)is formed,which prevents further twin propagation and leads to lateral growth of the twin.When non-cozone twin variants interact,twin de-twinning occurs and the multiple TTB interfaces forms.When non-co-zone twin variants interact,they can lead to twin de-twinning and promote twin nucleation at the matrix and the twin boundary.(3)Non-co-zone twin variants interaction will have a more pronounced workhardening effect than co-zone twin variants interaction and will be more conducive to subsequent twin formation if there are new twin nucleation sites in the stress concentration region of the interaction.(4)After co-zone twin variants interacting,the increase in internal stress in the region near the interaction is not significant,whereas after non-co-zone twin interaction,the increase in internal stress in the matrix region near the interaction will be significant,and the closer to the interaction region the more significant the increase in internal stress.(5)The interaction of non-co-zone twins increases the strength and plasticity of the material,and increases the strain hardening rate in the later stages of compression.