Study On Welding Process And Welding Defect Of Al-Li Alloy T-joints By Laser Welding

2060 and 2099 Al-Li alloy are the third generation of Al-Li alloy.They have the advantages of small density,small anisotropy,good thermal stability and good damage resistance.They have a wide application prospect in aerospace and other fields.Laser welding is a new type of welding technology which uses high energy density heat source for welding.It has the advantages of high energy density,small deformation and high production efficiency.In this paper,the welding process experiment of 2060-T8/2099-T83 Al-Li alloy T-joints by fiber laser welding with filler wire was studied to analyze the influence of different process parameters on the welding surface forming,the microstructure and mechanical properties of the T-joints.Finally classifying the welding surface defects of Al-Li alloy T-joints and analyzing the mechanisms.Firstly,the welding process experiment of 2060/2099 Al-Li alloy T-joints was studied and the influence of parameters on the welding surface forming was analyzed.When the laser incident angle is small,the welding stability is poor,the bubbles are difficult to escape,the number of welding porosity is much,the weld forming quality is deficient.The laser incidence angle is large,the welding forming is better and the porosity reduces.The bottom plate or stringer is penetrated when the center of the laser beam irradiates on the floor or the stringer,and the welding surface and back forming are good when the laser beam illuminates in the center of the welding.The welding seam is not fused or the convex degree is too large if laser power is too small,while laser power is too large,the welding seam burns seriously and easily and causes depression and other surface defects.Using high welding speed,the probability of the welding surface defects is small.Wire feeding speed is too small,the weld is not full enough,prone to depression and undercut while wire feed speed is too large,the fillet weld convexity is too large.Although the welding surface forming filling ER5356 wire is worse than that filling ER2A97 wire,the formation of cracks is reduced.The microstructure of the joint consists of fine crystal zone,columnar crystal and equiaxed dendrite.The microhardness of the weld is the lowest,and the tensile strength of the joint is lower than that of the base metal.Secondly,the weld defects of 2060/2099 Al-Li alloy T-joints laser welding were classified and the causes of defects were analyzed and the improvement methods were put forward.The weld surface defects are mainly bad surface forming defects,lack of surface fusion,holes and cracks and so on.Among them,the bad surface forming defects include surface depression,undercut,fillet weld convexity is too large,splash and its weld surface damage and the discontinuity of the scale.The fluctuation motion of the weld pool caused by the instability of keyhole in laser deep penetration welding is the main reason of the weld surface defects.The bad surface forming defects such as surface depression and undercut are mainly caused by the improper value of energy input and wire feeding speed.The lack of surface fusion defects is mainly due to lack of energy input,the inconsistent position of the laser and the welding wire and the small distance between them.The formation of pores can be reduced by decreasing the energy input,increasing the welding speed and increasing the laser incidence angle.The generation of cracks can be prevented by using the appropriate filler wire and controlling the welding speed.