| In the field of microelectronics packaging,batteries,relays,solar vacuum heat collecting tubes,composite materials and so on,glass and metal connectors are widely used.As a new connection technology,laser transmission welding has the advantages of non-contact,small pollution and easy control.It has great potential in the field of connection between glass and metal.In this dissertation,TC4 titanium alloy and high borosilicate glass 3.3 are used as the upper and lower materials of laser transmission welding.Because of the difference in chemical composition of the two materials,the welding strength is low.In this dissertation,laser surface treatment of TC4 titanium alloy is carried out to improve the laser welding strength of TC4 titanium alloy and high borosilicate glass.This dissertation explores the welding mechanism of this process,and optimizes welding process parameters and numerical simulation of temperature field.First,the surface of TC4 titanium alloy was pretreated with a semiconductor continuous laser and an oxide layer was formed on the surface of the titanium alloy.In the laser transmission welding test,the welding strength of the welded parts before and after the surface treatment of the titanium alloy was compared.It was found that the welding strength of the welded parts of the titanium alloy after the laser surface treatment was 4 times higher than that of the titanium alloy without the laser surface treatment.Secondly,from the point of view of micromorphology,it is found that the weld of TC4 titanium alloy after treatment and high borosilicate glass is broken after tensile test,and there are a lot of adhesion at the glass weld.It shows that the two materials have a strong connection effect during the laser transmission welding process,and the connection interface of the weld seam is entered.By line element line scanning analysis and analysis of the chemical composition at the weld,it is found that two kinds of material spread in the process of laser transmission welding,which is the important cause of the high welding strength.The effect of laser surface treatment on the surface contact angle of TC4 titanium alloy is studied by using the surface contact angle measuring instrument.It is found that the surface free energy of titanium alloy is increased after treatment,which is another reason for the improvement of welding strength.According to the force displacement curve and the weld profile in the tensile test,the tensile failure mode of the welded parts under different laser voltages is analyzed.When the voltage is low(440V),the form of tensile fracture is mainly brittle fracture.When the voltage increases(460V),the tensile fracture is mainly ductile fracture;when the voltage is increased,the voltage is mainly ductile fracture.At higher(480V),the connection structure of the weld is ablated and the glass sample ruptures.The results show that the high or low voltage will have a greater impact on the welding strength.Then,the Isight software is used to analyze the contribution rate of all experimental parameters of laser surface treatment experiment and laser transmission welding experiment to the welding strength,and select the experimental parameters with greater contribution rate to carry out the central compound experiment design.The experiment of laser transmission welding of TC4 titanium alloy and high borosilicate glass was designed by the response surface method(RSM)using Design-Expert V8 software.The mathematical model between the welding strength and the weld width was established,and the interactive influence of the process parameters on the welding strength and weld width was analyzed.In the end,three optimization criteria are optimized to obtain the maximum welding strength without considering other factors,obtain maximum welding strength at lower cost and obtain maximum welding strength under the smaller weld width,and obtain the optimal process parameters.Finally,the finite element model of the laser transmission welding process of TC4 titanium alloy and borosilicate glass is established,and the distribution law of temperature field during the experiment is simulated.The change rule of temperature field along with the change of process parameters is analyzed.The experimental values and simulated values of weld widths under the same parameters are compared to verify the reliability of the numerical simulation results.This dissertation lays a theoretical foundation for the study of laser transmission welding between glass and metal,and provides technical support for the laser transmission welding of TC4 titanium alloy and high borosilicate glass in actual industrial applications. |
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