Study On The Laser Welding Process And Characterization Of Joint Properties With Industrial Pure Zirconium R60702

R60702 industrial pure zirconium has excellent performance in corrosion resistance,wear resistance,fatigue resistance and high strength.It is commonly used in nuclear and chemical industries.Welding methods for R60702 include tungsten arc argon arc welding,vacuum electron beam welding,laser welding and so on.Owing to the remarkable advantages of laser welding in automation,precision,small joint deformation and high energy density,it is the main research direction in zirconium and zirconium alloy welding methods in the future.However,the study of R60702 laser welding only stays in the stage of technological exploration.There is little discussion on the relationship between microstructure and its properties in weld zone and heat affected zone.In this paper,2 mm thick R60702 industrial pure zirconium is invoked as the research object in this paper.The laser welding test on the surface of the zirconium plate is carried out to discuss the influence of different laser processing parameters(defocusing amount,laser power and welding speed)on the weld formation,thus forming good welded joint.The relationship between microstructure and properties of the laser welding jont is discussed and tested in combination with the test data of hardness,tensile and corrosion resistance.The results of surface surfacing test of 2 mm R60702 industrial pure zirconium show that the porosity in the weld is decreased with the increase of the amount of defocus,laser power and welding speed.The effect of defocus and laser power on the edge sharpness in the weldment is most obvious,and the influence of welding speed is relatively small.The optimum technological parameters are : laser power is 2000 W,welding speed is 35 mm/s,defocus is +4 mm,and upper and lower shielding gas flow rate is 50 L/min.The microstructure observation and analysis show that the parent material is a homogeneous alpha equiaxed crystal,and the fine grain zone in the heat affected zone is a strip and irregular alpha tissue,and the coarse grain region of the heat affected zone is the coarse irregular serrated tissue and the net shaped Weisman tissue,and the weld zone is the parallel strip martensite group and the basket Weisman structure.Comparing the grain size in each area,it is found that the grain size in the base metal area is the largest,followed by CGHAZ,and the second is the weld zone,and the grain size in FGHAZ is the smallest.The mechanical performance analysis shows that the mechanical properties of the welded joint specimens are similar to the direction parallel to the direction of the tensile stress in the TD,while the material shows the anisotropy of the material,that is,the specimen in the TD direction shows a strong modulus of elasticity and the yield strength,the lower ductility and tensile strength.The hardness of the weld zone is the highest in comparison with the hardness values in different areas.The hardness of the heat affected zone decreases from the weld to the base metal,and the hardness of the base metal area is the lowest.The corrosion resistance analysis shows that the weld has good corrosion resistance,the corrosion potential in 5 mol/L acetic acid is higher than that of the parent material,the corrosion current density is lower than that of the parent material,while the heat affected zone is slightly higher than that of the parent material.According to the stress corrosion sensitivity test of the welded specimen under this corrosion solution,it is shown that when the strain rate is 0.0001 mm/s,the parent material shows SCC sensitivity,and the ductile fracture occurs at the parent material.The results of texture analysis show that the BM region is a typical texture with double peak,and the texture group has a high dispersion degree,and the Euler angle of original alpha phase texture is(?=20°~60°,?=80°~90°,?=0~60°).In FGHAZ,textures of strong primitive alpha phase are retained,and new texture types(011 2)<2 111 >?(011 1)<12 11> and(011 0)<0001>are produced,and the texture of the original alpha phase texture in CGHAZ is basically the same,but it begins to focus on the Euler angle,(?=30°,?=90°,?=0~60°),the texture orientation,also the emergence of new texture(022 1)<11 02>.Focus on texture types in the weldment,the original texture is shown as the parent material(011 0)<101 1>.At the same time,according to the mean value of Schmidt factor in different regions,it can be found that the largest of the parent material area,that is,the column slip will occur in the parent material region at the time of drawing,which leads to the first plastic deformation stage and then the ductile fracture in the parent material area.