Research On Ultrasonic Assisted Laser Spot Welding Mechanism Of Dissimilar Materials

With the rapid development of modern industry,people have higher requirements for the performance of structural parts.Many high-end engineering and medical products require the performance of many kinds of materials.Among them,in recent years,by metal and plastic combination of products are favored.However,the physical and chemical properties of different materials vary greatly,so it is difficult to achieve high strength bonding.Therefore,the technology of metal-plastic dissimilar material bonding has high research value and application prospect.In this paper,2mm thick thermoplastic polyethylene glycol terephthalate(PET)and 0.7mm thick 316 L stainless steel are used as research objects.The experiment of metal side laser irradiation welding between metal and plastic is carried out by using 8kW fiber laser.It is proved that it is feasible to use pulsed laser energy to realize the connection between metal and plastics.The effects of pulse laser power,pulse frequency,pulse width and defocus on the macroscopic and microscopic morphology,interface area and mechanical properties of the joints during pulsed laser spot welding are studied.When the pulse laser power is 800 W,the pulse frequency is 12 Hz,the pulse width is 35 ms,and the defocus is 60 mm,speed of welding is 1.2m/min,the joint equivalent tensile strength is the highest,reaching 28.6 MPa.Laser texturing treatment is carried out on the surface of stainless steel,and pulse laser spot welding experiments are carried out on the basis of the optimum process parameters.The effects of metal surface texture on the macroscopic and microscopic morphology,interface area and mechanical properties of the joints are studied.The results showed that the equivalent tensile strength of the joints with texture increased to 37 MPa.Based on the optimum process parameters of the experiment,the ultrasonic assisted laser spot welding experiments of metal and plastics are carried out by using the ultrasonic assisted welding device designed by ourselves.The effects of ultrasonic power on the macroscopic and microscopic morphology,interface area and mechanical properties of the joints were studied under the condition of textured and non-textured metal surfaces,respectively.With the increase of ultrasonic power,the tensile properties of the joints increased first and then decreased.When the ultrasonic power is 120 W,the equivalent tensile strength of the joints with texture reached the maximum value of 45 MPa,which reached 86.5% of the strength of the PET base metal.From the microstructure of the cross section of the joint,it is found that under the action of ultrasonic wave,bubble pressure and the fluidity of the melt itself,the plastic melt is tightly bond with the metal and filled into the groove of the texture.Texture produces fins and grooves to form a "mutual chimera" effect.The EDS energy spectrum analysis shows that the content of carbon element is about 7% at the center of the interface and the content of carbon element in the groove is more than 70%.Furthermore,the metal side without residual PET after tensile fracture is measured by infrared spectroscopy,and the characteristic functional groups are calibrated.It is found that the CO group in PET reacted with metal elements in stainless steel and formed a high strength chemical bond.