2195铝锂合金T型接头双侧激光摆动焊接组织与性能分析

Microstructure and Mechanical Properties of Double-Sided Laser Swing Welding of 2195 Al-Li Alloy T-joints

2195-T87铝锂合金是轻质高强的新一代航空材料,但相比于传统铝合金,铝锂合金的焊接难度更高。基于铝锂合金蒙皮-桁条结构的焊接需求,采用激光束圆形摆动的方式配合Al-Si焊丝对2195-T87铝锂合金T型接头进行双侧激光摆动焊接,对比摆动激光焊接与无摆动激光焊接所得接头的焊缝成形与组织特征,并探讨了热输入、摆动频率以及摆动幅度对焊缝成形质量的影响,最终获得了优化工艺参数下的接头横向与轴向拉伸强度,分析了通过光束摆动改善焊缝成形质量、提高接头强度的效果。结果表明,采用高焊速、低热输入与中等摆动幅度和摆动频率的双侧激光摆动焊接可改善焊缝表面成形质量,抑制气孔生成,细化焊缝晶粒,缩小等轴细晶区尺寸,进而提高接头的横向与轴向拉伸性能,所得接头的最大轴向拉伸强度为267MPa,横向拉伸强度为420 MPa,对比无摆动焊接分别提高了123MPa和95MPa,达到了母材强度的45%和70%。

Objective 2195aluminum-lithium compound is a typical third-generation aluminum-lithium alloy.It has the advantages of being lightweight and high strength,making it very suitable for usage in the aerospace industry.Laser welding has concentrated heat input and minor welding distortion.Compared with traditional riveting technology,double-sided laser welding technology has the advantages of lower connection structure weight and higher work efficiency.However,Li’s addition makes aluminum-lithium alloy have higher welding porosity and thermal cracking susceptibility than traditional aluminum alloys.Therefore,it is difficult to weld aluminum-lithium alloys with lasers.On the contrary,laser swing welding can stir the molten pool to suppress the formation of welding defects and improve welding quality.The current research on double-sided laser welding of aluminum-lithium alloy T-joints mainly focuses on improving the welding quality by adjusting process parameters or improving the chemical composition of the welding wire but primarily for thin plates below 2 mm.In this study,we combine double-sided laser and laser swing welding technologies to realize double-sided laser swing welding of 2195-T 87 aluminum-lithium alloy T-joint.As a result,we obtain a joint with better surface forming,lower porosity,and greater strength.We hope this study can be a reference for the engineering application of double-sided laser swing welding of 2195 aluminum-lithium alloy T-joints.Methods 2195 aluminum-lithium alloy is used in this study.First,double-sided laser swing welding with circular swing method and traditional nonswing double-sided laser welding are used for welding 2195-T87 aluminum-lithium alloy T-joints with ER 4047 Al-Si welding wire.Then,visual techniques are used to compare the surface formation of welds obtained by different welding methods and process parameters.After that,the X-ray nondestructive testing method is used to compare the porosity of welds completed by laser swing and nonswing welding.Next,the metallographic microscope is used to observe and compare the cross-sectional morphology of different welds,and scanning electron microscope(SEM)is used to examine the joints and contrast the structural characteristics with the joint structure obtained by other welding methods.In addition,the electronic universal testing machine is used to conduct transverse and axial tensile tests on the welds completed by laser swing and nonswing welding and then compare their transverse and axial tensile strengths.Finally,SEM is used to examine the samples’cross sections and analyze their fracture mode.Results and Discussions The weld surface formed by double-sided laser swing welding is fuller and more uniform than that obtained by nonswing double-sided laser welding(Fig.6).The internal porosity of the weld obtained by nonswing double-sided laser welding is significantly higher than that of the swing welding.Double-sided laser swing welding reduces the porosity from 1.89%of the weld obtained by the nonswing double-sided laser welding to 0.52%(Fig.8).With the increase of welding speed,the weld’s ripples gradually become more detailed and uniform,the quality of weld formation is improved,the penetration width is steadily reduced,and the thermal impact on the skin is reduced(Table 3).With the swing amplitude and frequency increase,the ripples on the weld’s surface become finer,enhancing the surface shape.However,when the swing amplitude and frequency are too high,the weld’s surface dramatically collapses,and when the swing amplitude is too high,the wall panel is not penetrated(Tables4--5).Compared with nonswing double-sided laser welding,the average diameter of equiaxed crystals in the middle of the weld obtained by double-sided laser swing welding has been reduced from 21to 13μm(Fig.10).In addition,the average diameter of the equiaxed fine-grained region has been reduced from 44to 23μm(Fig.11).The joints obtained by double-sided laser swing welding have an axial tensile strength of 267 MPa and transverse tensile strength of 420 MPa,which increase by 123 MPa and 95 MPa,respectively,compared with nonswing welding(Fig.12).Microporous aggregation fractures mainly characterize the fractures on the side of the welds.They have intergranular and transgranular fracture characteristics.The fracture on the side of the base metal is a combination of quasi-cleavage and microporous aggregation fractures(Figs.13--14).Conclusions This study combines double-sided laser and laser swing welding technologies to realize a double-sided laser swing welding of 2195-T87aluminum-lithium alloy T-joint.Double-sided laser swing welding with circular swing method is used to obtain 2195-T87aluminum-lithium alloy T-joint with firm surface forming and low porosity.The porosity rate is reduced from 1.89%to 0.52%.Compared with conventional double-sided laser welding,double-sided laser swing welding can significantly refine the equiaxed crystal area in the middle of the weld by beam swinging and stirring the molten pool,and significantly reduce the size of the equiaxed,fine-crystal area to enhance the joint’s load-bearing capacity.The average diameter of the equiaxed crystal in the middle is reduced from21to 13μm,while the average diameter of the equiaxed,fine-crystal region is reduced from 44to 23μm.The obtained joints have maximum axial and transverse tensile strengths of 267and 420MPa,respectively.Compared with nonswing welding,they increased by 123and 95 MPa,respectively,reaching 45%and 70%of the base metal strength.Our study shows that double-sided laser swing welding can design 2195-T87aluminum-lithium alloy joints of better surface forming,lower porosity,and greater strength.