Numerical Simulation And Experimental Study Of Tube-high Pressure Shearing Of High Purity Aluminum

The grain size and mechanical properties of the samples after severe plastic deformation are closely related to the extent and the homogeneity of plastic deformation.The inhomogeneity during deformation will adversely affect the properties and application of the material.Therefore,the strain field distribution during deformation is very important for the preparation and mechanical properties of ultrafine-grained materials.A simple shearing process is driven by the stick friction between the dies and sample under high hydrostatic pressure,such as High Pressure Torsion(HPT)and tube-High Pressure Shearing(t-HPS),the main results for inhomogeneity deformation are as follows:(1)the strain gradient described by the strain analytical solution,but this is also a major feature of these deformation,from which gradient structural materials can be prepared;(2)the local deformation inhomogeneity caused by local slipping in the process of deformation;(3)the local deformation inhomogeneity caused by the structural and parameters of the die.As the latter two points will cause the local deformation inhomogeneity,which will affect the microstructure and properties of the material seriously,so it needs to be reduced or avoided as far as possible.Therefore,in order to prevent local slipping during t-HPS and understand the influence of die structure on strain distribution,it is necessary to quantitatively analyze the influence of the process parameters.In view of the above problems,this paper investigated through FEM simulation,with the confirmation of experimental observation.In this paper,5N high pure aluminum(99.999%)is taken as the research object.And MSC.Marc is used to investigate the contact normal stress distribution of tube wall in the compressive stage.The aim is to reduce the local slipping caused by inhomogeneous contact normal stress distribution of tube wall.DEFORM is used to investigate the influence of die structure on the strain inhomogeneity in the t-HPS shearing stage.The aim is to reduce the local inhomogeneity in the t-HPS process and reduce the material loss as much as possible.Moreover,5N aluminum was used to verify some of the simulation results qualitatively,and the main conclusions are as follows:(1)Through the finite element analysis of the t-HPS compressive stage,it is found that the contact normal stress distribution of the tube wall in the combined pressurization method is more homogeneous than that in the methods of pressurized on both ends of the tube and pressurized using the wedge effect,which is helpful to control and reduce local slipping in the t-HPS shearing process.(2)Through the finite element analysis of the t-HPS shearing progress,it is found that the axial strain distribution is inhomogeneous,and a “Dead metal zone”(DMZ)forms at the end edge corner of the tube samples,due to the friction effect on the ends of the samples.The axial deformation inhomogeneity of the sample is qualitatively described by the DMZ axial proportion.The axial strain inhomogeneity and the Dead metal zone was confirmed by the experimental of the high pure aluminum after t-HPS processing.(3)For t-HPS pressurizing using wedge effect,the contact normal stress gradient cannot be eliminated by adjusting the relevant parameters,so it is difficult to avoid local slipping during t-HPS.The half cone angle has little effect on the strain inhomogeneity of the t-HPS.Moreover,the axial strain inhomogeneity of the sample can be reduced by decreasing the ends feature size,but the material loss increases meantime.(4)For combined pressurization method,with the decrease of the half cone angle,the contact normal stress inhomogeneity of the tube wall increases.Although the Dead metal zone change little,the decrease of the sample height will lead to the increase of the axial strain inhomogeneity and the material loss.Under the condition of this paper,increasing the half cone angle properly in the range of 2.5°? 10°can increase the homogeneity of axial strain distribution and reduce the material loss.As the ends feature size increases,the homogeneity of the contact stress increases,which is beneficial to alleviate the local slipping of the sample,but it will decrease the axial strain inhomogeneity,the Dead metal zone will be increased.Therefore,on the premise of keeping the axial homogeneity of the contact normal stress of the sample,the ends feature size is properly reduced to increase the axial deformation homogeneity.(5)The radial strain gradient is related to strain-hardening exponent in both ideal t-HPS described by theoretical equation and practical t-HPS described by FEM.This feature of t-HPS stands out from other SPD processes like HPT,where although materials parameters like the strain hardening exponent have an obvious effect of strain distribution,although it does not have any influence on ideal corresponding processes.This makes practical t-HPS behavior more predictable in its analytical formation than any other SPD processes,and places it in an advantageous position in understanding the basics of deformation physics through the coupling between practical experiments and theoretical approaches.