Study On The Mechanism Of Damage Defects In Rotary Extrusion Process Of Inner Ring Cylinder

The inner shell of magnesium alloy as a typical light alloy structure is widely used in aerospace and aviation fields.Such components usually adopt traditional methods such as welding,casting,and cutting.but these manufacturing methods have many disadvantages:low mechanical properties,poor load bearing capacity.,and high defect rates.Therefore,rotating extrusion technology is proposed for this type of component to achieve its overall plastic forming.However,in rotary extrusion,damage and fracture directly determines success or failure of the process and forming quality of the component,and also becomes one of the important research directions of this process.Therefore,to describe the damage and fracture in rotary extrusion accurately is the subject of this paper.In this paper,AZ31magnesium alloy was used as experimental material and the damage evolution behavior during the process is analyzed.The main contents of the dissertation include the following four parts:Through Gleeble3500 hot torsion testing machine and Deform-3D simulation software,they were used to perform corresponding physical tests and numerical analysis.It was determined that the Normalized C&L ductile fracture criterion is applicable to the damage situation in rotary extrusion of AZ31 magnesium alloy.After comparison between effective tests and predicted results,the critical value of damage of material changes from 1.659 to2.289,under the conditions of deformation temperature of 320°C⁴00°C and strain rate of0.01¹s^-1.Deform-3D analysis software was used to construct numerical analysis models.Five factors were selected:friction coefficient,axial extrusion speed,radial extrusion speed,rotary speed and deformation temperature.A total of 25 groups of orthogonal tests were designed to research the process of rotary extrusion of AZ31 magnesium alloy inner ring cylinder.In the process of rotary extrusion,damage factor distribution of components in ring region is not uniform,and damage factor at the upper end of ring is large;and the equivalent strain of the wall and the inner ring is large,resulting in the grain was refinement in the region,which effectively improves overall performance of the component;due to the structure of punch work,a certain flash will be generated during the rotary extrusion.Crack defects were analyzed by FEM to determine the location of crack damage.It is distributed at the upper of inner ring cylinder of forming ribs,and damage source location is located inside blank.After the affecting of degree and regularity on damage value and equivalent strain of rotary extrusion is analyzed,and the best process parameters were determined in combination with actual conditions.According to the ranking of influential factors,it is analyzed that radial rotary extrusion alone has little effect on the damage of components,and the influence rule of axial extrusion speed Vz and punch radius R on the evolution of damage is mainly discussed.The forming limit diagram is obtained under different Vz and R.The results verify that when punch radius R is small,the plastic deformation of material is greatly affected and damage value is relatively high.The optimized forming processes which satisfy rotary extrusion are:the axial extrusion speed Vz=5mm/s and the fillet radius R=8mm.According to the above research,the inner ring cylinder of AZ31 alloy is tested by rotary extrusion.Microstructure observation and mechanical performance is experimented on the location of extrusion part.The results verify that the grains in the position of ring were clearly refined,and cracks were found at the upper end of ring.Through bending experiments,the performance of rings in rotary extrusion was better than those ordinary rings.