Research On Mechanism Of High Frequency Microvibration Laser Welding

"Industrial 4.0"points out the direction for the development of manufacturing industry.Welding,as the key processing technology in the manufacturing,also becomes the hot research field under the trend.With the continuously rapid development of science and technology,some of the traditional welding technology have been unable to meet the increasing demand of the modern economic market,and it is urgent to develop a new welding technology or some developing traditional welding technology.High frequency of micro vibration laser welding is a new type of welding technology,based on the traditional vibration welding and developed along with the laser technology.It takes the advantages of both,and can effectively decline the welding residual stress,reduce the porosity,delay the crack extension,refine the microstructure,and increase the microhardness etc.Besides,combined with laser welding,it can also increase the welding speed and raise the working efficiency.But its mechanism has insufficient,and requires further study.In this paper,The self-developed high-frequency vibration device is used to control and study the high frequency of micro vibration laser welding.Inconel 718 nickel-based superalloy is selected as experimental material,which is widely used in aero-engine machining.The research mainly includes two parts,the high frequency of micro vibration laser welding process and its mechanism research.The welding formation,the morphology and composition of microstructure,the microhardness with different vibration parameters are analyzed and compared through test and analysis methods,such as OM,SEM,microhardness test,in order to conclude the the influence rule of vibration parameters on the welding formation,and the microstructure and properties.The temperature field of high frequency vibration laser welding is simulated based on ANSYS finite element analysis software,and the finite element analysis model is established.Through the experimental study on the combined with numerical simulation method,from the perspective of solidification theory and thermodynamics,the weld microstructure evolution process and law of Inconel 718 alloy high-frequency vibration laser welding is analyzed,and the microstructure evolution mechanism of welding thermal process are revealed.When the laser power is 4000W,the welding speed is 0.02 m/s and the defocusing amount is-15 mm,under no vibration conventional laser welding process,the welded joint is a"nail"shape in the cross-section,the surface is like a string of beads.After applying vibration,when the vibration frequency is 919 Hz,the vibration acceleration is0.2 m/s~2,the heat input is 266.7 kJ/m,?which is the depth-to-width ratio of weld and?which is the nail head placeholder ratio match better,the weld is good.Under lower frequency,with smaller vibration acceleration,the weld with slender and smaller nail head placeholder is obtained.Under higher frequency,bigger vibration acceleration,the weld with more slender and more nail head placeholder is got.After vibration,in the nail head,microhardnesses in the weld zone decrease,the average microhardness in heat affected zone increases,and both of the maximum and minimum value have no obvious change.In the nail body,the microhardnesses in weld zone have no significant change,the average microhardness in heat affected zone increases,and both of the maximum and minimum values increase.When the vibration acceleration is 20.2 m/s~2,as the vibration frequency increases,the overall joint's microhardness is in a downward trend,but the microhardness in heataffectedzonehasnoobvious change,andthe weldzone are first increase and then decrease.The precipitated phase in the base metal are composed by slender?"phase,the massive block delta phase and MC(Nb,Ti)type carbide.After laser welding,it exists dendritic segregation in weld zone,which is mainly the gamma/Laves eutectic.As the vibration acceleration increases,the number of the white interdendritic precipitate phase is less and less,or even little.Based on ANSYS finite element software,a heat source model composed by double ellipsoid and cylinder is established for the temperature field of the high frequency microvibration laser welding of Inconel 718.In the simulation experiment,laser power is4000W,the welding speed is 0.02 m/s,the model is bulit in a symmetric way,its geometric size is 100mm×25mm×5mm.And it is driven by APDL parametric programming language of cyclic loading for the moving heat source.the whole welding heating time is 5s,and the end time is 1000 s,which returns to the room temperature by air cooling.The actual measurement results of temperature and weld appearance size are in good agreement with those obtained in the simulation,and the error is within 5%.The reliability of the simulation test is confirmed.During the welding heating process,the start and end time of the highest temperature in the molten pool is higher than the stabilized one which is about 2466?.It is the quasi-stable state heat conduction process.The heat affected zone is narrow,and the temperature gradient is larger.The temperature in the heated region rises to the highest temperaturein a relatively short time,and with the distance between the weld centerline increasing,the rate of temperature rise decreases.During the cooling process,the cooling rate is about 110.2?/s.With the distance between the weld centerline increasing,the cooling rate of the temperature field decreases.The residence time of the high temperature in weld zone is 0.125 s,and it is 0.5 s during 700~1000?period.For that reason,there are few high temperature strengthen phase,and lots of low melting eutectic gamma/Laves in the weld,which are the reasons for dendritic segregation.The temperature range in heat affected zone mainly is from 684?to 684?.But in the local narrow region near the fusion line,the temperature is close to 1544?.For that reason,low melting eutectic ia remelted,and the grain boundary is gathering and coarsened,indicating softening zone and liquefied crack,which is the most weak link.