Research On Laser Welding Process And Defect Suppression Of CP-Ti

Titanium has excellent properties such as light weight,high strength,nonmagnetic,and corrosion resistance.Its excellent corrosion resistance is effective in meeting the corrosiveness of seawater and ocean atmosphere.Therefore,it also has the reputation of “marine metal”,and in processing and forming,Titanium,like other common metal materials,can be subjected to techniques such as welding,casting,and plastic forming by some conventional processing techniques,so titanium materials are popular in various marine engineering fields.The main forming methods of titanium tubes include seamless titanium tubes and welded titanium tubes.Seamless titanium tubes are difficult to form and costly.Therefore,in areas that are sensitive to production costs,welded titanium tubes are mostly used.In actual production,TIG welding is often used for the welding of titanium,but the welding speed is slow and the efficiency is low.After the TIG welded joint is coarse and the plasticity is seriously reduced,a certain degree of embrittlement will occur,and the laser welding has a small heat input.The welding speed is fast,the processing precision is high,and the like,and the welding of titanium and titanium alloy is quite flexible.Therefore,this paper proposes laser welding of CP-Ti plates under different parameters,and seeks to improve the welding efficiency of pure titanium production.This paper constructs a set of industrial pure titanium laser welding and TIG arc assisted laser welding experimental system,including laser,TIG welding machine,walking platform,high-speed photography system.Based on the laser welding experiment system,this paper studied the laser welding procedure of CPTi plate,the causes of back splash and undercut in laser welding process,and found the inhibition method of defects,which laid a foundation for efficient welding of industrial pure titanium TA2.The solid experimental and theoretical basis has important guiding significance for the efficient welding of industrial pure titanium TA2 in actual production.The results show that the laser power,welding speed,welding power,welding speed,defocusing amount and laser incident angle have the greatest influence on the weld formation,the laser power and welding speed,then the defocusing amount.According to the principle of energy saving and low efficiency,the experiment selected laser power of 2400 W and laser speed of4.8m/min,and conducted docking experiments under this parameter.The docking experiment found that the weld was formed under this parameter.Observing the high-speed photography results,it can be seen that the back splash of the welding mainly has three forms of continuous splash,periodic splash and no splash.All continuous back splashes are accompanied by a back keyhole penetration test panel,and the back keyhole penetration test panel can also be observed in the presence of periodic splashes,and when there is no backside splash,the back melt pool is stable and cannot be observed.Keyhole,so it can be considered that the back splash will only occur when the keyhole penetrates the test plate,and when the laser power is below 3000 W,the effect that the back keyhole cannot penetrate the test panel can be achieved only when the defocus amount is increased to + 5mm,so it is proposed to increase the defocus amount to suppress the laser welding of industrial pure titanium plates spatter.The study found that there are two main reasons for the formation of laser welding undercut: on the one hand,laser welding forms a keyhole,steam formed by metal evaporation ejects toward the back wall of the keyhole,and the friction of steam against the back wall of the keyhole makes the molten pool liquid.The metal weld is flowing backwards,so that the liquid metal filled to the edge of the weld is insufficient.On the other hand,the laser welding itself has a faster welding speed and a faster cooling rate,so that the liquid metal can not spread to both sides of the weld,thereby forming a bite.side.TIG arc assisted laser welding has a good inhibitory effect on undercut defects occurring in single laser welding.On the one hand,the original single laser welding has a large temperature gradient and a short cooling time.When the auxiliary TIG arc is added,the cooling time of the weld is prolonged,so that the liquid metal has a longer time to spread on both sides of the weld;on the other hand,By observing high-speed photography,it can be found that the arc is in front and the laser does not melt the base material when the laser is behind,but it plays the role of preheating,which makes the bath temperature higher and is more conducive to the flow of liquid metal.Comparing the microstructure of single laser weld and TIG arc assisted laser welding,the heat-affected microstructure is not much different,but the heataffected zone of TIG arc assisted laser welding is obviously wider,which is mainly due to the larger heating range of the arc.From the viewpoint of weld microstructure,there are zigzag ? phase and needle ?? phase in the microstructure of the weld under the two welding methods,but the difference is that there is almost no equiaxed ? phase in the single laser weld,and There are twins in the center of the weld,which is mainly due to the faster cooling of the weld pool during single laser welding.Similar to the single laser welding head,the same weld zone has the highest hardness value,the heat affected zone is the second,and the base metal hardness is the lowest.The reason why the hardness of the weld and the heat-affected zone is slightly increased is also the coarsening of the grain,and there is a part of the serrated ? phase in the weld,resulting in a high hardness of the weld,but overall,the joint hardens is not serious.Comparing the tensile test results of the TIG arc assisted laser welded joint and the single laser welded joint,the strength of both the weld and the heat affected zone is higher than that of the base metal because both of them are broken at the position of the base metal.The joints are all qualified,but therefore,the measured tensile strength is the strength of the base metal,and the fracture morphology is also the fracture morphology of the base metal.Therefore,both the mechanical properties and the fracture morphology are combined.There is no significant difference.