Study On Mechanical Behavior And Adiabatic Shearing Sensitivity Of Variable Form ZK61 Magnesium Alloy

As the lightest metal structural material at present,magnesium alloy has many advantages such as high specific strength,specific stiffness,easy to recycle,good electromagnetic shielding performance,excellent casting and machining performance,etc,which can meet the requirements of light weight and integration.It has broad application prospects in modern transportation,electronic and communication products,machinery and other fields.Among them,Mg-Zn-Zr-based magnesium alloy as the best high-strength magnesium alloy at present,and ZK61 magnesium alloy is one of the typical high-strength magnesium alloy.In the forming process,the mechanical properties of the magnesium alloy produced by the traditional casting method are not ideal,and the high strain rate forging shape can eliminate the casting defects,which can greatly improve the mechanical properties of the magnesium alloy,however,forging is easy to cause anisotropy of the material,thereby limit the promotion and application of the magnesium alloys.Based on this,the mechanical properties of casting and forging variant ZK61 magnesium alloy under quasi-static and dynamic loading were studied,which can provided some theoretical guidance for the improvement of mechanical properties of the alloy.In this paper,the high-strain rate forging deformation of casting ZK61 magnesium alloy was carried out by air hammer.The microstructure,mechanical properties and adiabatic shear sensitivity of the casting,forging variant and oriented samples of the alloy were investigated.The effects of deformation and orientation on the mechanical properties and adiabatic shear sensitivity of the alloy were discussed.The following conclusions were obtained:The high strain rate forging deformation has a great influence on the microstructure of ZK61 magnesium alloy.With the increase of forging deformation,the casting defects in the grain structure gradually disappear,and the grain size gradually getting smaller.When the deformation amount is 15%,the casting defects such as slag inclusions and pores in the grains basically disappeared,there are still a few casting defects at the boundary of the two phases.When the deformation amountis 20%,due to the mutual extrusion of the grain boundaries,twinning begins to appear at the boundary of the two phases,and twins begin to separate the grains in individual grains.When the deformation amount is 30%,with the amount of deformation increases,a large number of fine grains appear at the intersecting grain boundaries.No dynamic recrystallization grains were observed under optical microscope.When the amount of deformation is 40%,fine grains disappear at grain boundaries,and grain size becomes uniform.In the forging billet with 30%deformation,the micro-morphology of the samples with different orientations is quite different.The microstructures along the TD and ND directions show many fine grains at the grain boundaries,and the number of fine grains in the TD orientation is more than that in the ND direction.No fine grains appear at the grain boundary of the RD oriented sample,and the whole grain shows an elongated state.The high strain rate forging deformation has the significant effect on the mechanical properties of ZK61 magnesium alloy.The true stress-strain curve analysis of the casting and deformed samples under the condition of quasi-static shows that the microstructure deformation at 30% and 40% has higher strength,and the deformation of the microstructure at 15% has the best plasticity,while,the microstructure with 40% deformation has the worst plasticity,the microstructure with deformation at 30% has higher strength and better plasticity,and the strength and plasticity of the casting microstructure sample in a lower position;Under dynamic loading,the strength of the sample gradually increases with the increase of the deformation amount,but the intensity has small increment.In the adiabatic shear test,the stress-time curve of the ZK61 magnesium alloy microstructure specimen and the morphology of the shear zone show that the adiabatic shear sensitivity is: 15%,casting,20%,30%,40%.The mechanical properties of different orientation microstructures of ZK61 magnesium alloys are different.Under the condition of quasi-static,the Rolling Direction(RD)specimens show the worst plasticity,but has the best strength;the normal direction(ND)specimens has higher strength,but bad ductility;the strength and plasticity of the transverse direction(TD)sample are in the middle position.Under dynamic loading conditions,the transverse direction(TD)and the normaldirection(ND)of the forged ZK61 magnesium alloy has few anisotropic characteristic of the dynamic mechanical behavior,while the Rolling Direction(RD)have conspicuous anisotropic characteristic of the dynamic mechanical behavior comparing with TD and ND.The different plastic deformation mechanisms in the different orientations specimens results in the anisotropy of the dynamic mechanical behavior in the ZK61 magnesium alloy specimens.Through the analysis of stress collapse time of three orientation specimens,the adiabatic shearing sensitivity is: RD,TD,ND.