AZ31 Magnesium Alloy Sheet Accumulative Roll Bonding-Bending Deformation Technology And Its Microstructure And Properties

The world's demand for lighter weight has grown since the 21 st century.No matter what transportation is used in daily life,such as automobiles,or household appliances such as computers and mobile phones,light and high-performance metal materials are required.Magnesium alloys as lightweight metal materials have more and more extensive application prospects in light weight.However,the rolled conventionally magnesium alloy sheet has poor plasticity and low strength,which limits its application range.In response to this problem,this article uses industrially-produced AZ31 magnesium alloy sheet as the starting material,combines cumulative rolling process and bending deformation process,successfully prepared ARB(Accumulative Roll Bonding abbreviation ARB)plates,AE plate(ARB plate bended Plates,referred to as AE plates)and PE plates(initial plates undergo bending,denoted as PE plates),are expected to develop a forming process capable of producing toughened magnesium alloy plates,clarifying The influencing rules of process parameters(temperature,cumulative strain,annealing Process)on the microstructure and properties of the magnesium alloy sheet,the Accumulative Roll Bonding-bending magnesium alloy sheet,and the bending-deformed magnesium alloy sheet,reveal the related mechanism,and the main conclusions are as follows:(1).The cumulative rolling temperature has a great influence on the surface quality of the rolled plates.The surface cracking of the rolled plates at 350°C was severe,and the surface cracks at 450°C were almost completely eliminated.There was no crack on the surface of the rolled plate at 550°C,High rolling temperature can eliminate the surface cracks of the rolled plates.There were a lot of shear deformation shear during the process of cumulative rolling at 450°C and 550°C,which result in obvious shear bands microstructure in the ARB2 magnesium alloy sheet.The V-shaped shear zone has a large number of small dynamic recrystallized grains near the interface of the plate.Its size was about 600nm-2?m,and its dynamic recrystallization is likely to be closely related to the interface welding.High-temperature accumulative roll bonding is more conducive to the effective welding of the interfacial rolling interface,which promotes the disappearance of the ARB sheet interface in the optical metallurgical microstructure;the work hardening and the interface welding of the ARB sheet affect the tensile strength of accumulative roll bonding AZ31 magnesium alloy sheet.The greater the work hardening is,the greater thestrength of the sheet is,and the worse the welding condition of the interface between the one and the other the strength of the sheet is,The combined effect of the two is the reason that the tensile strength of the 450ARB2 sheet and the 550ARB2 sheet are almost the same.For 550 °C accumulative roll bonding 1,2,3,4 and 5 cycles sheets,there are a large number of V shear bands in the microstructure.With a large number of dynamic recrystallization,the dynamic recrystallization grain size is between 500 nm and 1?m.With the increase of the cycle number,the sheet elongation does not decrease significantly,and its value is stable at around 10%-12%.The plate fracture shows a certain ductile fracture characteristics,its tensile strength first increased from 260 MPa to 300 MPa,and finally stabilized at about 300 MPa.The main reasons for this are the work-hardening,significant grain refinement,and increase in the number of recycle passes resulting from accumulative roll-to-rolling,which leads to more twins and a significant increase in the number of twin boundaries leading to a further increase in strength.(2)The tensile strength of the sheet gradually decreases with the number of cycles.The reason is that with the increase of the cycle number,the number of interfaces of the rolled plate is more,if the interface welding strength is not good,it is not conducive to the improvement of the tensile strength of the plate;with the increase of the number of cycles,the rolled plate bent and deformed non-basal orientation grains increased significantly,resulting in a decrease in the yield strength of the plate from 215 MPa to 198 MPa,an increase in elongation from 12.1% to 22.8%,The reason why the proportion of non-basal oriented grains in the magnesium alloy sheet is significantly increased s related to two aspects,On the one hand,accumulating the amount of strain accumulated in the early stage of the roll-bonded magnesium alloy sheet contributes to bending deformation and increase the specific gravity of non-base oriented grains.On the other hand,the bending deformation can promote the increase in the number of non-base oriented grains in the magnesium alloy sheet,and both are essential for the significant increase in the specific gravity of non-base oriented grains,and they are indispensable.(3).ARB3 sheet,AE3 sheet(ARB3 sheet after bending and deformation,denoted as AE3 sheet),after annealing at 300 °C at different times,the grain size with the annealing time from 2min to 30 min,the grain size gradually increased.The interface between ARB3 plate and AE3 plate with the increase of annealing time shows a better trend in the welding of the interfacial rolling interface.The complete metallurgical welding occurs at the interface.The increase of the annealing time is conducive to the welding of the overlapped rolling interface.High temperature in the accumulative rolling process is an importantbasis for subsequent annealing to improve the interfacial bonding interface.Appropriate post-annealing time is an important way to further improve the interfacial bonding interface while controlling the grain size;for magnesium alloys with a large amount of historical cumulative large strain.For the sheet,the annealing can promote a significant increase in the specific gravity of the non-basal orientation grains,and the larger the historical accumulated strain,the greater the increase in the specific gravity of the non-basal orientation grains in the subsequent annealing process;For magnesium alloy sheet with historically large cumulative strain,bending deformation can promote the further increase of the specific gravity of non-basal oriented grains of magnesium alloy sheet in the subsequent annealing process;bending deformation and annealing treatment change the grain orientation of magnesium alloy sheet and weaken magnesium.There are some necessary conditions for the achievement of the two important approaches to the texture of the base material of the alloy sheet.The necessary condition is that the magnesium alloy sheet must have a large historical cumulative strain before bending or annealing.The combined effect of bending deformation and annealing promotes a bimodal texture of the roll-bending plate.