Microstructure And Forming Properties Of TA17 Titanium Alloy Plate

Titanium alloy,as an advanced lightweight metal material,has been widely used in the field of aerospace for its high strength,low density and good corrosion resistance.Therefore,high-strength titanium alloys such as TA17 are no longer just used in aerospace,but have become potential candidate materials for structural components in other industries such as automotive,Marine and chemical industries.However,there are many difficulties for the manufacture of titanium alloys,which includes low formability,large deformation resistance and springback when forming at room temperature.Stamping forming is an advanced manufacturing technology,which has been widely used in aerospace.The fracture behavior is always a seriously considered problem.Therefore,it affects the application in the field of aerospace parts processing.TA17 titanium alloy(nominal component is Ti-4Al-2V)is near-? titanium alloy which can be applied to high temperature and high pressure conditions.It presents high temperature resistance,good welding performance and water corrosion resistance,high static and circulating strength and its room temperature forming performance is better than TC4 titanium.The feasibility of using TA17 titanium alloy in aircraft skin parts was studied.Therefore,it is necessary to study the microstructure and forming performance of TA17 titanium alloy plate to judge the feasibility of the application of aircraft skin parts.The main research work and results are reflected in the following aspects:(1)In this work,the commercial TA17 sheet had annealing treatments performed on it to obtain different initial microstructures.The tensile test was conducted at both room and high temperatures.The influence of initial microstructure on forming characteristic was studied.The experimental results show that the mechanical properties of TA17 are sensitive to the initial microstructure before deformation.Annealing treatment could change the mechanical properties of the TA17.The comprehensive mechanical properties of the TA17 are enhanced after annealing of 850?/2h/AC comparing with these after other annealing processes,because a finer equiaxed primary ?-phase is obtained.(2)In order to reduce the experimental cost and shorten the development cycle,a feasible progression-dependent method based on the finite element simulation was adopted to determine the process of localized necking to fracture,which was also used to predict the forming limit diagrams of TA17 titanium alloy plate with different microstructures.The effect of microstructure on the forming limit with 3 kinds of TA17 has been studied at room temperature.The TA17 titanium alloy with the equiaxed microstructure provides the best performance on the forming limit.(3)The uniaxial tensile tests were performed on TA17 alloy sheet.The true stress-true strain curves reveal that the flow stress decreases with the increase of the temperature and the decrease of the strain rate.The numerical models of the hot uniaxial tensile,dome stretching and deep drawn cup tests have been adopted to establish the principal strain distributions for TA17 titanium alloy.The FLCs of TA17 are obtained with different temperatures and strain rates.The results presents the limit strain decreases with the increasing strain rate and the decreasing temperature.(4)The finite element simulation analysis of stamping forming process of aircraft skin parts made of TA17 titanium alloy plate was conducted.The distribution of strain cloud diagram and forming limit diagram of airplane skin parts were obtained.Hot stamping of aircraft skin parts of TA17 titanium alloy plate at temperatures above 850? will not crack.It is shown that TA17 titanium alloy plate can be used in the manufacture of airplane skin parts when it is formed at high temperature.In a word,the mechanical properties and microstructure of TA17 titanium alloy sheet were studied by tensile test a,forming experiment and microstructure observation.The forming limit diagram was established at room temperature and high temperature.It provides theoretical guidance for mechanical properties research,forming limit prediction and process optimization of titanium alloy.