Effect Of High Frequency Micro-vibration On Microstructure And Fatigue Properties Of Laser Welding

Vibratory welding is a new technology welding,its theory is vibratory stress relief,it means applying the mechanical vibration to the base metal during welding at the same time.Its purpose is to refine grain and improve the mechanical property of welding joint.Fatigue life is one of the welding joint's property,and is one of the most important service performance parameters of the welding joint.In this paper,the industrial pure iron was used to high frequency micro-vibration laser welding.The microstructure of welding joint and fatigue fracture were invertigated through metallographic observation,microhardness,and SEM.The effect of high frequency micro-vibration parameters on microstructure and fatigue properties of laser welding was analysed and the results of the fatigue test were verified by numerical simulation and further deepening the research on the mechanism of the fatigue damage of high frequency micro-vibration laser welding.The results of the high frequency micro-vibration laser welding tests showed that mechanical vibration can increase weld depth in the laser welding,the higher the vibration frequency is,the smaller the grain size of welding joint is.When the frequency of mechanical vibration was selected close to the material natural frequency,the smaller vibration acceleration is,the smaller grain size of the welding joint is.As the vibration frequency was 118Hz,the vibration acceleration was 36.1m/s~2,the microstructure refinement of welded joint was the most significant.As the output power of laser welding was 3000W,the defocusing distance was-10mm,the welding speed was 1.2m/min,the microhardness was declined.The resulted of fatigue test showed that the fatigue life of welding sample was decreased compared with the base metal under the same external fatigue load.When thewelding speed was 1.2m/min and output power was 3000W,the vibration frequency was 789Hz,the vibration acceleration was 36.1m/s~2,or the vibration frequency was1186Hz,vibration acceleration was 36.1m/s~2,the fatigue life was increased,and the fatigue load was 53%?_b at the same time.When the vibration frequency was 1186Hz,vibration acceleration was 195.3m/s~2,the fatigue life was decreased.When the fatigue loads were54%?_b and 55%?_b,the fatigue life was increased because of the vibration.In fatigue fractograph,The number of fatigue sources was mostly one,while the vibration frequency was 789Hz,the vibration acceleration was 36.1m/s~2 or the vibration frequency was 1186Hz,vibration acceleration was 195.3m/s~2 was found two or three fatigue sources,which were located at the edge of the sample fracture corner and weld porosity.When the fatigue load was 52%?_b,the source of fatigue was at the edge of sample in laser welding without vibration.The Bay Ridge in the fatigue propagation region of most of samples was clearly visible,but they weren't seen when the fatigue load was 52%?_b and 54%?_b.When the vibration frequency was 1186Hz,the vibration acceleration was 195.3m/s~2,the porosities failing forming the fatigue source were seen in the fatigue propagation regions;the final rupture region of fatigue was small,and were like hill,deflation,dimple,intergranular fracture.Combined with the microstructure and fatigue property of welded joint,the results showed that under higher loading stress the high frequency micro-vibration could increase the fatigue life in laser welding,but had no significant effect on fatigue life;when the vibration frequency was closed to the damping vibration frequency of the base material,the fatigue life was reduced...