The Effect Of Grain Orientation And Pre-existing Twins On The Compressive Deformation Behavior Of Rolled Magnesium Alloys

As the lightest metallic structure material,Mg alloy and its alloys,called “t e green engineering materials in st entury”,are attracting growing concern for the application in the electronics,automotive,aerospace and other fields.Due to the hexagonal closed packed(HCP)crystal structure,Mg alloys have limited independent slip systems at room temperature.Moreover,traditional rolled or extruded Mg alloys usually have a strong(0001)basal texture,which induces a strong anisotropy during the deformation.To a great extent,all these defects restrict the wide applications of Mg alloys.Studying the influence of deformation conditions on the deformation mechanism and microstructure evolution of Mg alloys is of great theoretical significance and practical value to optimize the plastic deformation process and develop advanced Mg alloys with high performances.In present work,we choose hot-rolled AZ31 Mg alloy sheet as experimental material.The plastic deformation behavior and anisotropy of Mg alloy during uniaxial compression were studied.In addition,hot-rolled Mg alloy sheet was pre-compressed along TD direction at room temperature to introduce extension twinning in order to investigate the influence of the pre-existing twins on the compressive mechanical properties and the plastic deformation behavior of Mg alloys.The microstructure evolution of Mg alloys during deformation was analyzed by metallographic microscopy(OM),electron backscatter diffraction(EBSD),and scanning electron microscopy(SEM).t low tem erature ° and ig strain rate,the compression flow curves,strain hardening rate curves and strength of the rolled Mg alloy strongly depended on grain orientation and external loading direction,showing a high degree of anisotropy.Since the non-basal slips dominated the early period of deformation,the as-received sample compressed along ND exhibited higher strain hardening rate at 200?.But for as-received samples compressed along RD,45o and pre-compressed samples compressed along ND or RD,their strain hardening rate curves were complex and could be divided into three distinct stages because they were favorable for the activation of {10-12} twinning at low temperature.2)With the increasing temperature ?),the strain rate sensitivity index(m)increased and the anisotropy of the rolled Mg alloy gradually decreased.The activation of the non-basal slips and the dynamic recrystallization(DRX)softening caused by the dislocation movement made the compression flow curves and the work hardening rate of the as-received samples and the pre-compressed samples gradually tend to be similar to each other,which could effectively avoid local stress concentration and resulted in a uniform deformation during hot working.3)Compared to those of as-received samples,the yield stresses of pre-compressed samples compressed along RD at room temperature,100?,150? and 200? were increased by 54,58,52 and 51 MPa,respectively.But the yield stresses of pre-compressed samples compressed along ND at room temperature,100?,150? and 200? were decreased by 99,75,36 and 6 MPa,respectively.However,compared with the as-received samples of RD,the yield stresses still increased and its yield strength remained about the same at 0~200?.4)At 200?,continuous dynamic recrystallization(CDRX)was the main DRX mechanism in the as-received sample compressed along ND.In addition to CDRX,{10–12} twinning related DRX(TDRX)also played an important role in the as-received samples compressed along RD and the pre-compressed samples compressed along ND or RD.Discontinuous dynamic recrystallization(DDRX)was also initiated in the as-received sample during compressing,but it was a rather small proportion.However,with the temperature further increasing,the role of DDRX in deformation was increasingly important.The DRX mechanism was eventually changed to DDRX in the as-received and pre-compressed samples,as the temperature rose to 300?.