| TC4 titanium alloy is concerned by people because of its corrosion resistance and high temperature resistance.It is mainly used in aerospace and other fields,and has become an ideal material urgently needed in manufacturing industry.However,due to its poor plasticity at room temperature,it is difficult to carry out large curvature bending deformation at room temperature,which causes the difficulty to put the alloy into actual production application.In order to improve the usability of TC4 titanium alloy in the actual production process,it is necessary to understand its basic mechanical properties and study the main factors affecting its formability.Based on the hot stretching test and bulging test of TC4 titanium alloy,the yield,flow and fracture properties of the material under high temperature were analyzed.The forming limit curve of TC4 titanium alloy at high temperature was drawn.The deformation mechanism was revealed by observing the microstructure,and different constitutive models were established to predict the mechanical property curve and forming limit curve of TC4 titanium alloy at high temperature,respectively.Finally,the predicted forming limit curve was input into ABAQUS to analyze the influence of temperature and strain rate on dome height（LDH）.Details are as follows:Thermal tensile tests were carried out on TC4 titanium alloy at temperatures ranging from 650℃to 750℃and strain rates ranging from 0.001s-1 to 0.1s-1.The stress-strain curves under different test conditions were obtained.The effects of temperature and strain rate on mechanical properties were analyzed.According to the test results,it can be found that TC4 titanium alloy has obvious temperature sensitivity and strain rate sensitivity.EBSD was used to observe the original specimen and the tensile specimen.It was found that the microstructure of the specimen after high temperature treatment changed significantly,revealing the deformation mechanism of the material.Then,five constitutive models（Arrhenius model,JC model,m-JC model,Hensel-Spittel model and modified Hensel-Spittel model）were established based on the hot tensile test data,and a new n-JC model is proposed.The prediction accuracy of the established model was evaluated by calculating the average absolute relative error（AARE）and correlation coefficient（R）of the established model.It can be concluded that the AARE value and R value of HS model are5.24%and 0.98794 respectively,and the prediction accuracy of HS model is the highest among all models.However,JC model has the worst predictive ability,with AARE value and R value of 41.1%and 0.84726,respectively.n-JC model has a much higher prediction accuracy than JC model,with AARE value and R value of 14.4%and 0.95322,respectively.TC4 titanium alloy was tested by bulging test equipment,and the concave die and blank holder were heated by high-frequency induction coil.The forming limit curve was obtained at 700℃-0.1s-1.In order to improve the efficiency of obtaining the forming limit curve,the M-K model was established to predict the forming limit curve under other experimental conditions.Then,the forming limit curve obtained from the test was input into ABAQUS software to simulate the bulging test process,and the rupture shape of the simulated parts was consistent with that of the test parts.The forming limit curve predicted by M-K model was input into ABAQUS to simulate the bulging process under strain rates of 0.1s-1-650℃,0.1s-1-700℃,0.1s-1-750℃,650℃-0.001s-1,650℃-0.001s-1 and650℃-0.001s-1.According to the simulation results,the LDH value was measured,and the formability was better with the decrease of strain rate and the increase of temperature.In this paper,the basic mechanical properties and formability of TC4 titanium alloy were studied,and the flow characteristics and formability of the material were obtained under temperature range of 650℃-750℃and strain rate range of 0.001s-1-0.1s-1.It provides a theoretical basis for the subsequent TC4 titanium alloy multi-dimensional forming. |
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