Deformation And Strengthening Mechanism Of Thin-walled Workpiece Of TA15 Titanium Alloy During Hot Power Spinning

The power spinning of titanium alloy gained wide attention as the requirements of lightweight and high performance for weaponry.However,there were many influence factors during the power spinning process.The interaction between spinning mandrel,blank and rollers has an important influence on the stability of spinning process.The mechanical property anisotropic of the workpiece after deformation was evidently due to the predominant HCP crystal structure of TA15 titanium alloy.Therefore,the properties homogeneity of spinning parts need more study.The finite-element analysis indicated that the axial stress was greater than radial stress while the tangential stress was relatively small during shear spinning process.The deforming zone was approximate to near plane strain and tangential strain was close zero.The radial stress was greater than axial stress and the tangential stress is smaller in roller contact zone of tube spinning.Radial compressive and axial tensile deformation was arisen in the condition of three dimensional compression stresses.And the value of tangential stress was determined by the difference between radial and axial metal flow.As non-symmetric distribution of rollers,the distribution of tangential stress in deformed zone exhibit non-periodic change and the radial spinning force of each roller was different,which leads to eccentricial force exerted on the mandrel and affects the stability of spinning process and reduced the as-spun parts precision.The number and its central included angle along circumferential direction of mandrel determined the actual feed ratio,the profile and area of contact zone under the each roller.Furthermore,the proportional relationship was found between area of contact zone and actual feed ratio,the change of spinning force has positive correlation with contact area.The deflection measurement system of eccentric force exerted on the mandrel was designed and the resultant of FE simulation and mechanical analysis was verified.A non-symmetric stagger spinning was proposed to solved the problem of eccentric force exerted on the mandrel during asymmetric spinning,improved the flexibility and stability of spinning process on two-rolls machine.During the multi-pass shear spinning of TA15 titanium alloy,the grains crushed firstly.With the increasing of spinning passes and thickness reduction,the radial force of rollers increased.The grains elongated simultaneously in axial and circumferential directions and refined obviously.The tensile strength of the as-spun conical parts decreased firstly and then gradually increased during multi-pass shear spinning.The compressive yield strength in circumferential direction keeps increasing slowly during multi-pass shear spinning since the circumferential strain was quite limited and the effect of grain refinement improved the increase of compressive yield strength.The grain orientation rotated to the direction of <10-10> and <11-20> and the texture in basal slip <0001> was weakened gradually firstly during shear spinning.With the increasing of thickness reduction,the grains were compressed and elongated along generatrix direction.The crystal orientation of grains concentrated and <0001> textural orientation distribution was regenerated.The changing of average Schmid factor of basal slip {0001}<11-20> during shear spinning showed that the as-spun conical parts after multi-pass shear spinning was less anisotropy relative to original blank.The properties uniformity of as-spun parts improved markedly.The grains were elongated and fibred in axial direction during multi-pass hot power spinning.With the thickness reduction,the tensile strength in axial direction of tube was gradually higher than that in circumferential direction during multi-pass single dircetion spinning while the mechanical properties in axial and circumferential direction was relatively close during cross spinning.During single direction spinning,the grains average misorientation between c axis and ND decreased from 60.7° to 25.4° gradually in axial direction of tube while it changed little in circumferential direction,caused obvious anisotropy of the as-spun tube.In multi-pass cross spinning process,the grains average misorientation between c axis and ND decreased simultaneously from 58.3° to 24.3° in axial direction and from 49.1° to 16.1° in circumferential direction.After multi-pass single spinning,the average Schmid factor of basal slip {0001}<11-20> in axial direction was apparently smaller than that in circumferential direction.While in multi-pass cross spinning,the average Schmid factor in circumferential direction also decreased obviously.The conical-cylindrical parts with uniform thickness and high properties were obtained combined the variable-thickness tube spinning and hot flaring.The wrinkle in cylindrical zone and the crack in deforming zone were effectively avoided by controlled the temperature range in different zones and the axial section thickness distribution of the variable-thickness tube.The flaring ratio and homogeneity of thickness were improved.The conical-cylindrical part was integral formed through shear spinning preforming and multi-pass power spinning.The lamellar structure of rolling blank was crushed during shear spinning.And then the crushed grains elongated along axial and circumferential direction of the part during multi-pass power spinning.The microstructure of deformed parts was refined and the mechanical properties of workpiece were strengthened about 20%.