Effect Of High Frequency Micro-vibration On Microstructure And Fatigue Fracture Behaviour Of Laser Filler Wire Welded Joints

In this paper,the method of coupling laser filler wire welding with mechanical vibration is used to improve the macroscopic morphology,microstructure,and microhardness of 316 stainless steel laser filler wire welded joints by applying mechanical vibrations,reducing the residual stress and increasing the tensile properties of welded joints,thereby improving the fatigue performance of laser filled wire welded joints.In the process of laser filler wire welding of 316 stainless steel,the influence of different mechanical vibration parameters on the performance of welded joints was analyzed by changing the frequency of mechanical vibration.Observe the macroscopic morphology and microstructure of the weld through an optical microscope,the microhardness tester measures the microhardness of the cross section of the weld to analyze the effect of mechanical vibration frequency on the morphology and hardness of the welded joint.Residual stress test on 316 stainless steel welded joints by blind holes method.Tensile test on 316 stainless steel with tensile tester.Fatigue experiments were performed on 316 stainless steel with a high-frequency fatigue tester to study the effect on fatigue life of welded joints with different mechanical vibration conditions.The fracture behavior was analyzed by scanning electron microscope observation of fractures.Studies have shown that the macroscopic morphology of the weld as the vibration frequency increases during laser filler wire welding,that can be effectively improved,littler spatter,and more beautiful the formation.At the 1055 Hz vibration frequency,the equiaxed grains are the most in the weld,and the grain refinement is the highest.When the laser power is 4000 W,the welding speed is 0.02 m / s,the defocus amount is-10 mm,the wire feeding speed is 250 mm / min,the vibration frequency is 1055 Hz,and the vibration acceleration is 65.6m / s2,Welded joints with better forming,higher grain refinement and improved mechanical properties can be obtained.Compared with 316 stainless steel base material,the micro-hardness of vibration-assisted laser filler wire welded joints is significantly improved,at 0 Hz,524 Hz and 1055 Hz vibration frequencies,the microhardness of welds increased by 6.7%,8.7%,and 11.4%,respectively.Because the hardness of the weld is closely related to the structure,the finer the grain,the higher the hardness;the tensile strengths of welded joints were 561 MPa,590MPa,and 605 MPa,respectively;sections of tensile samples;the shrinkage rates were 38.5%,41.2% and 49.2%,respectively.Residual stress tests showed that the residual stress of welded joints increased at a vibration frequency of 524 Hz,and the residual stress of welded joints decreased at a vibration frequency of 1055 Hz.This is because the vibration of the weld during the solidification process will destroy the growth of columnar dendrites,refine the structure uniformly,reduce defects such as pinholes and cracks,and improve tensile properties.The fatigue fractures of 316 stainless steel base material and vibration-assisted laser filler wire welded joints are composed of three regions: fatigue crack source,fatigue propagation region and fatigue fracture zone.The fatigue life of the welded joint decreases with increasing fatigue stress load.Compared with the fatigue limit strength at 0 Hz and 524 Hz vibration frequency,the conditional fatigue limit strength of the welded joint at 1055 Hz vibration frequency is the best,reaching 267 MPa.Features such as river patterns,cleavage steps,and secondary cracks can be observed in the base material and the fatigue fracture expansion zone with different vibration frequencies,and a large number of fatigue glow stripes are generated,which are cleavage fracture.In the fatigue fracture zone,fatigue cracks propagate faster,the area is smaller,and morphology such as dimple appears.