Study On Microstructure And Mechanical Properties Of Ti-5322 And Ti-1300 Alloy Welded Joints

With the improvement of the comprehensive strength of national defense science and technology,space shuttles,weapons and equipment are developing towards light weight,high speed and high performance.Medium strength titanium alloys can no longer meet the application requirements under special conditions,and the need for high strength titanium alloys and research are becoming more and more urgent.Welding is an important method of joining titanium alloys.Therefore,more and more attention has been paid to how to improve the structure of high strength titanium alloys and improve the comprehensive properties of welded joints.In view of the paper,the relationship between weldability,microstructure evolution of welded joints and mechanical properties of Ti-5322 and Ti-1300 high strength titanium alloys for different purposes has been studied in this paper.Ti-5322 alloy is a low-cost armor titanium alloy.The connection and repair of armor structure need welding.Tungsten Argon Arc Welding has the characteristics of simple welding equipment,good welding quality,especially outdoor welding repair.Therefore,the state of base metal,post-weld heat treatment process and the composition of welding wire for Ti-5322 alloy are studied to effect of microstructure and mechanical properties of Ti-5322 TIG welding joint.Ti-1300 alloy is a kind of aeronautical structure titanium alloy,which requires high welding quality.Electron beam welding under vacuum conditions can avoid air pollution,narrow weld zone and heat-affected zone,and good welding quality.Therefore,base metal status and post-weld heat treatment process for Ti-1300 alloy were studied.The effect of joint structure and mechanical properties.Through the analysis of two kinds of high strength titanium alloy welded joints,the following conclusions are drawn:The state of base metal(R,ST and STA)has little effect on the grain size,structure and morphology of the weld zone.The weld zone of Ti-5322 joint is thick columnar crystals in different states.In the weld zone of Ti-5322 joint,there are fine alpha phase and a small amount of metastable beta phase.In the weld zone of Ti-1300,there are only metastable beta phase and no second phase precipitation.Postweld heat treatment has a great influence on the structure of the weld zone,mainly the size and quantity of intragranular alpha phase,which has little effect on the morphology of the grain in the weld zone.A wider grain boundary alpha phase will precipitate in the grain of the weld zone after solidification and aging,which is unfavorable to the performance of the welded joint.Fine alpha phase will precipitate in the weld zone after solidification and aging at low temperature,which can obviously improve the strength of the weld zone and reduce the plasticity.High temperature aging and dual aging welding joints have good Strength-plasticity matching.Under different heat treatment conditions,the weld zone is still coarse columnar crystals,and the size is basically unchanged.TC4 welding wire can reduce the concentration of beta stable elements in Ti-5322 weld zone,and form a long flake-like alpha phase.The size distribution of alpha phase is not uniform,and the stress distribution is easy to be uneven during tension,which results in the hardness and plasticity of joints are slightly lower than that of bulk welding wire.There are strong textures in the weld zone and base metal zone of Ti-1300 alloy R-state welded joint,and the orientation is consistent.This is mainly due to the fact that the coarse columnar crystals in the weld zone take the unmelted base metal as nucleating particles.Post-weld solution aging heat treatment can not change this state.The grain orientation of ST and STA base metals is random after recrystallization,but the texture of weld zone is obviously weakened and not completely disappeared due to the existence of some small angle grain boundaries in the base metals.The welded joint of Ti-5322 alloy has good comprehensive properties with yield strength of 888 MPa and elongation of 13%.For Ti-1300 alloy welded joints,the base metal is Solution-Aging state after welding,and the base metal is Solution-Aging state after welding and dual aging state after welding.The yield strength is above 930 MPa,and the elongation is above 16%.It has good Strength-plasticity matching.