Study On Droplet Transfer And Microstructure And Properties Of SMA490BW Weathering Steel Weld By Laser Welding With Filler Wire

Laser welding is a high-energy beam welding method with high weld aspect ratio,narrow heat affected zone,low distortion and high welding efficiency.However,the welding process is complicated by to the addition of a wire.It is worth assessing the interactions between the laser and the wire,since they can affect the stabilization of droplet transition.The effect of the welding parameters on droplet transition was assessed on a high-speed camera equipment.Meanwhile,a physical model for droplet force evaluation was created by force analysis of the spatter particle to analysis the influence factors of weld forming.In addition,the text chose SMA90 BW weatherproof steel as base metal to study on the mechanism and process parameters of laser welding with filler wire.The results show that the transition models included spreading transition,liquid bridge transition and globular transition.with increasing H from 0mm to 4mm(the vertical distance between the wire and panel)value,the droplet mode changed from spreading transition to liquid bridge transition,and to globular transition.Among these modes,liquid bridge transition was the most stable.Droplet transition frequency decreases rapidly with increasing H from 0mm to 4mm value.The droplet transition and welding process showed stability at H=1mm.The growth position of droplet is mainly divided into the position of the end face and the position of the section.The droplet of end face position can increase the height indirectly,resulting in the change of droplet transfer and frequency.A physical model of droplet force analysis was created in different transition models.The spread of the transition mainly submitted to the force of the molten pool.In the liquid bridge transition physical model,the droplet was transferred to the molten pool in the state of balance.Meanwhile,the droplet entered into contact with the molten pool under an unstable force during globular transition.Laser power has a great influence on weld geometry parameters.With increase of laser power from 4kW to 5.5kW,the weld depth increased by 22% and the width increased by 40.4%.With increase of defocus from-10 mm to 10 mm,the weld depth and width were reduced firstly then were increased.In addition,the weld depth and width could reach the maximum value of 7.1mm and 6mm respectively,when the defocus distance was-5mm.With increase of weld speed from 0.6m/min to 0.96m/min,the weld width decreased by 39.7% and the changing tendency of weld width was greater than the weld depth.With the increase of feed speed from 1m/min to 4m/min,the weld depth decreased by10%.The optimum process parameters of 8mmSMA490 BW weatherproof steel welding was acquired: laser power is 5.5kW,welding speed is 0.72m/min,feed speed is 1m/min,H is 1mm.The microstructure of metal filling area was bigger than the laser area in laser welding with filler wire.In the upper metal filling area,the micro-hardness reached to 310 HV which appeared in the heat affected zone.The location where tensile specimens fractured was the base metal.The impact toughness of laser welding with filler wire was greater than laser welding in-20 degrees Celsius.