The Study On Hot Deformation Behavior And Heat Treatment Of Ti-5322 Low Cost Titanium Alloy

Titanium alloy has broad development space in aviation,aerospace,chemical,biomedical and other fields due to its high comprehensive mechanical properties and other high characteristics.However,the titanium alloys also have some shortcomings,such as low elastic modulus,high yield ratio,and easy springback,which makes it difficult to deform plastically.Therefore,the stress-strain curves of Ti-5322 low-cost titanium alloy are obtained by thermal simulation compression test.The constitutive equation reflecting the relationship between flow stress and thermal deformation parameters is constructed by analyzing the stress-strain curves,a processing map of Ti-5322 alloy combined with microstructure analysis is drawn to guide the selection of molding equipment and the formulation of the molding process.Furthermore,the alloy solid solution aging process is systematically studied to optimize the heat treatment process parameters.The hot deformation behavior of Ti-5322 alloy with initial equiaxed microstructure were investigated using isothermal compression tests at temperatures of 750¹050℃and strain rates of 0.01¹0s^-1,to optimize its hot workability.Constitutive equations expressing the flow stress as a function of the strain rate and deformation temperature in theα+βdouble-phase region and theβsingle-phase region were established.Furthermore,processing maps are developed on the basis of the dynamic materials model.The results show that the activation energy of Ti-5322alloy in double-phase region and theβsingle-phase is 397.66KJ/mol and244.24KJ/mol,respectively,which indicates that the deformation mechanism of Ti-5322 alloy in single-phase and dual-phase regions is different.According to the processing maps,the optimal processing parameters of Ti-5322 alloy are 750⁸25℃,0.01⁰.05s^-1;925⁹75℃,0.01¹s^-1;and 1000¹050℃,0.05¹s^-1.Microstructure observations reveal that mostαlamellae are globularized in the double-phase region,and dynamic recrystallization is the principal type of microstructure evolution in the single-phase region.In addition,three instability domains are detected in the processing maps,and these instability domains are confirmed by the presence of microstructures with wedge cracking and adiabatic shear bands,which should be avoided during hot working.Through the solution treatment of Ti-5322 alloy,it was found that when the solution was below the transformation point,the primaryαphase decreased with the increase of the solution temperature,and the volume fraction of theβphase increased;above the transformation point,the primaryαphase is completely dissolved into theβphase,and the higher the temperature,the coarser the grains.Some new secondaryαphase plates precipitates aging process,which plays a precipitation strengthening role.As the aging temperature increases,the secondaryαphase grows up and the volume fraction reduced,leads to a decrease in the strength of the alloy and an increase in the plasticity.The Ti-5322 alloy heat treatmented samples were subjected to room temperature tensile test.It was found that compared with the solid solution and aging inβsingle-phase region,the strength and plasticity of the alloy after solid solution in（α+β）double-phase region and aging treatment is more excellent,so it is most suitable to select the solution treatment in double-phase region.