The Study Of Rotating Extrusion For AZ80Magnesium Alloy Cup

Magnesium alloy is the lightest metallic structural material, is one of the best weaponrylightweight materials. The cup is the most representative structure in the defense industry,transportation and other fields. Therefore, the production of formed magnesium alloy cupwith high strength and high toughness is of great significance. At present, the magnesiumalloy products are mainly produced by casting production which causes many defects andpoor mechanical properties. The plastically formed magnesium alloy products have goodmechanical properties, but the improvement of magnesium alloy components performance islimited by conventional plastic forming method. The severe plastic deformation like largestrain rolling, equal channel angular pressing and high pressure torsion can greatly enhancethe mechanical properties of magnesium alloys, but it is usually only used for the preparationof high-performance materials which results in high cost and the limited size in thepreparation of the materials.In this paper, a new rotating extrusion whose punch have grooveson the end face is come out to form the magnesium alloy cups. The method can not onlyobtain the effect of severe plastic deformation, but also can reduce the performance differenceof the cup in axial and circumferential direction. However, the related basic problem of suchnew forming technology has not been reported at home and abroad.Firstly, based on the power balance method, the thesis determines the unitdeformation force of the punch when the cup is backward extruded, and on this basis, theheight calculation formula of the cylinder upsetting deformation under the punch isestablished. Using the axial symmetrical stream function, kinematically admissible velocityfield was proposed in the rotating extrusion process. It provides a theoretical basis for the sizeof cup structure and analysis the metal flow.Based on the height calculation formula of the cylinder upsetting deformation zone in thelower punch, when rotating extruded cup is put forward, the internal and external diameter ofcup components must meet dD0.821. In terms of AZ80magnesium alloy cup, the finite element method is used to simulated analyze the variation law of punch’s axial loadings whenthey are acted by the punch with grooves and the variation law of deformation strain field andvelocity field when they are forming as well as.The influence of the extrusion speed of punchand rotational speed on folding defect of metals which are extruded into the grooves of punchis analyzed.The results show that comparing with the traditional backward extrusion, the axialloadings of punch is greatly reduced, rotating backward extrusion can obtain larger effect ofplastic deformation, plastic deformation zone extends greatly.Rotating extrusion can get spiralfibrous tissue and the performance difference of the cup in axial and circumferential directionis reduced.The lower the extrusion speed of punch is and the faster the rotation speed is, theeasier folding defect appears.Finally, the finite element method is used to explore the influence of the parameters offorming process (axial speed and rotational speed,friction coefficient),the end face taper of thepunch, the number of grooves of the punch, the grooves structure size on the rotatingextrusion process of AZ80magnesium alloy cup.The results show that with the increase ofaxis rotational speed, the average value of equivalent strain of formed workpieces is large,and the plastic zone of blank expands significantly. The lower the extrusion speed is and thehigher the rotational speed around axis is,the more severe the degree of deformation is and thesmaller the axial loading of punch is. The change of the friction coefficient has little influenceon the maximum equivalent strain of formed workpieces. When the friction coefficient is0.2and0.15which are intermediate values,the workpiece deformation is more uniform.Thebigger the friction coefficient is,the bigger the deformation of punch is.When the frictioncoefficient is the smaller value of0.05, the end face of punch also has a slightly deformation.The equivalent strain is significantly great when punch has grooves on the end face. The morethe number of grooves on the punch, the greater the maximum value of the equivalent strain is,the greater the average value of the equivalent strain is and the smaller the axial loading ofpunch is.The average value of the equivalent strain of the formed workpieces whose coneangle of the punch is1.5o is greater than that whose cone angle of the punch is15o.Thedeformation is more uniform and the axial load is smaller when adopting1.5o. Comparing with the traditional backward extrusion, after blanks are rotational extruded, the average grainsizes are smaller, and the percentage of dynamic re crystallization is higher.