A Study Of Laser Welding Process Of Al-Li Alloy In T-joint

Al-Li alloy with low density,high specific strength and high specific rigidity,good corrosion resistance and fatigue resistance,and is an excellent aircraft structural material.It is a common type of aircraft panel structure for T-joint,and compared with riveted joint,the laser welded joint can reduce the weight of the structure and improve the efficiency of production.In this paper,the technology of laser welding with filling fiber of aluminum alloy T-joint is studied.First of all,the basic process of laser welding for T-joint is studied,and the influencing factors of cross section forming,surface forming and porosity defect are analyzed.The study shows that process parameters influencing cross section shape of the weld by the laser power,welding speed,laser incident angle,offset etc..In the case that the heat input is not changed,the weld penetration depth on the bottom plate can be reduced by reducing the laser incident angle and increasing the offset.Reasonable length of welding wire is the premise to obtain good weld surface appearance.After optimizing the length of filling wire,reasonable selection of laser power and wire feeding speed is a necessary condition for good appearance of the weld surface.Before welding,the aluminum lithium alloy can be cleaned properly,and the number of the large porosity in the weld can be reduced by increasing the offset and reducing the laser incident angle.Secondly,the microstructure and mechanical properties of 2A97/2099 Al-Li alloy for T-joint were analyzed.Joint consists mainly of base metal,heat affected zone(HAZ)and weld metal.Affected by the laser heat source,the second phase particles in the heat affected zone grow up,and liquefaction phenomenon appeared near the fusion line of semi melting grain boundary.The weld zone is a typical as cast microstructure,from the fusion line to the weld center,there are fine equiaxed grain zone,columnar grain zone and coarse equiaxed grain zone in turn.The grain boundaries and the grain center in the weld respectively appeared Cu element segregation phenomenon,and the formation of second phase particles with different compositions.Micro-hardness test results show that the hardness of the weld is lower than that of base metal,and the hardness of heat affected zone is lower than that of base metal,but higher than that of weld seam.The transverse tensile test results of the joint show that 93% of that of parent material,and the tensile deformation is very small,the crack initiation at weld toe,and then along the side of the base plate of the fusion line,finally broken in the bottom plate.The fusion zone on the skin side is the weakest part of the joint,Fracture shows the characteristics of intergranular fracture and transgranular fractureConcludes with a discussion of the process method for controlling transverse tensile strength.The transverse tensile strength of aluminum alloy T-joint relates to the skin penetration,and it is a way to obtain high strength joints by reducing the incident angle of the laser beam so that weld penetration depth is less than half the thickness of the floor.