Study On Micromechanical Behavior Of Laser Welded Joint Of TA2 Titanium Alloy Based On Crystal Plasticity Finite Element Method

Laser welding is one of the important welding methods for titanium and titanium alloys.There are large differences in the grain morphology and grain size of the welded joint zones,which lead to the differences in the constitutive relations of each zone of the joint.However,in the current stress and deformation simulation of welded structures,the entire joint is calculated using the same constitutive model,resulting in a large error between the calculation results and the actual situation.The study of mechanical behavior is an important part of the study of constitutive relations.It is difficult to study the tensile mechanical behavior of welded joints by experimental means because of the small area size of welded joints.The crystal plasticity finite element method is an effective method to calculate the plastic deformation of materials in the grain size.Therefore,based on the crystal plasticity finite element method,the mechanical behavior of laser welded joint zones of industrial pure titanium TA2 is studied in this topic.The main contents are as follows:(1)Based on the EBSD experiment,the representative volume unit models of weld center zone,weld zone near the fusion line,fusion zone,heat affected zone and base metal zone of TA2 laser welded joints of industrial pure titanium were constructed.(2)The crystal plasticity parameters of commercial pure titanium TA2 were calibrated by using phenomenological crystal plasticity model,and the reliability of crystal plasticity parameters was verified.The simulated stress-strain curve was in good agreement with the tensile test curve on the whole.(3)The effects of grain number,strain rate and loading direction on the mechanical behavior were studied.The results showed that the model of about 100 grains was the most suitable as a representative volume unit model;Under quasi-static condition,strain rate hardening effect exists in weld center zone,fusion zone and base metal;In different loading directions,the maximum difference of yield strength of columnar crystal model is 14.4%,showing a certain degree of anisotropy.(4)At 0.001 strain rate,the average grain size is 25 μm、23.9 μm、29.6 μm,the yield strength of columnar crystal model of the weld center zone is 361 MPa,387 MPa and 372 MPa respectively;The average grain size is 22.1 μm、23.2 μm、40.4 μm,the yield strength of columnar crystal model of the weld zone near the fusion line is 366 MPa,368 MPa and394 MPa respectively;The average grain size is 29 μm、36 μm、50.1 μm,the yield strength of equiaxed crystal model of the fusion zone is 354 MPa,382 MPa,390 MPa respectively;The average grain size is 32 μm、29.7 μm、33.2 μm,the yield strength of equiaxed crystal model of heat affected zone is 313 MPa,321 MPa,312 MPa respectively;The average grain size is 26.6 μm、26.3 μm、26.5 μm,the yield strength of equiaxed crystal model of base metal is 326 MPa,322 MPa and 316 MPa respectively.