Research On Hot Power Spinning Forming Process And Quality Of Magnesium Alloy Cylindrical Part With Inner Ribs

To adapt to the innovation and development of manufacturing industry in new century,the requirements for lightweight,high performance and low energy consumption of structural material have been increasing in the fields of automation,aerospace,aviation and military sector.Magnesium alloy with advantages such high specific strength and high specific stiffness is the most lightest metal structural material.As one of high strength magnesium alloys,ZK61 magnesium alloy has characteristics of excellent mechanical properties,good heat resistance and corrosion resistance.In terms of material and structural design,magnesium alloy and cylindrical part with inner ribs can well satisfy the requirements of components for lightweight and high strength.However,magnesium alloys exhibit poor ductility at room temperature,and difficulty in filling the inner ribs exists during the plastic deformation of cylindrical part with inner ribs.As one kind of forming method with point-by-point and continuous plastic deformation,metal spinning can effectively enhance the ductility of material,and hot power spinning becomes an effective way to overcome the poor ductility of magnesium alloy and form cylindrical part with inner ribs.Therefore,investigation on the hot power spinning process of magnesium alloy cylindrical parts with inner ribs has significant theoretical value and practical meaning,not only in controlling the occurrence of forming defects but also in improving the forming quality of spun parts.The method of solution treatment was proposed to eliminate the non-uniformity of microstructure for ZK61 magnesium alloy extruded cylindrical blank,the influence of solution parameters on the microstructure and mechanical properties was investigated;the hot processing map of solution-treated ZK61 alloy based on dynamic material model was established via high temperature axial compression test,the deformation behavior and flow instability of magnesium alloy were analyzed.To realize the lightweight and high strength of component,the structure of cylindrical part with trapezoidal inner ribs was designed.The hot power spinning forming process was analyzed and corresponding forming equipment was developed,the indexes including roundness,straightness,sunken ratio of ribs back,saturation of inner ribs and inhomogeneity of inner ribs were proposed to evaluate the forming quality of cylindrical part with inner ribs.The hot power spinning process of magnesium alloy cylindrical part with inner ribs was simulated via ABAQUS software,the stress,strain and material flow of spun workpiece during hot power spinning were discussed.The forming defects occurred during hot power spinning of magnesium alloy cylindrical part with inner ribs were analyzed,and the influence of process parameters on the forming quality and microstructure of spun workpiece was investigated experimentally.The results show that the non-uniformity of microstructure for ZK61 alloy extruded cylindrical blank can be effectively eliminated by solution treatment at 425? for 1h;under 250-300?,the flow stress of ZK61 alloy exhibits three stages such as work hardening,dynamic softening and steady flow;under 350-450?,the flow stress enters steady stage firstly and then increases continuously.According to the hot processing map of ?=0.6,the power dissipation factor ??30% under ? ?0.1s-1,which is beneficial for DRX;The power dissipation factor decreases with the increase of strain at the same temperature and strain rate,and the DRX is weakening;the flow instability region occurs under T?425? and ? ?1s-1,which increases with the increasing of strain.The simulation results of magnesium alloy cylindrical part with inner ribs during hot power spinning confirm well with experimental results.The thinning of material at cylindrical wall of spun workpiece is larger than that at inner ribs.The material at cylindrical wall undergoes compressive strain along the radial direction,while tensile strain occurs along the tangential and axial directions;The material deformation at inter surface of inner ribs undergoes compressive strain along the tangential direction,while tensile strain occurs along the radial and axial directions.The main forming defects such as sunken of ribs back,inhomogeneity of inner ribs,orange peel of ribs surface were produced during hot power spinning of magnesium alloy cylindrical part with inner ribs.The temperature under 300-350?and feed rate under 0.4-0.6mm/r are beneficial for hot power spinning of magnesium alloy cylindrical part with inner ribs.The full ribs of cylindrical part with 4mm height inner ribs could be obtained under thinning rate of 75% of tube with 8mm thickness while thickness reduction is 1.5 times as much as rib height of spinning part.Small grains and uniform microstructure of spinning part could be obtained under a temperature of 300? and a feed ratio of 0.4mm/r.