Research On Welding Characteristics Of 6005A Aluminum Alloy Laser Filler Wire Welding

The use of aluminum alloy for high-speed train body structure materials has become an inevitable trend in the development of the transportation industry.Lots of welding demands of 6005A-T6 aluminum alloy for high-speed trains are include small deformation,low residual stress,high mechanical properties and excellent corrosion resistance performance,etc.This paper studies the welding characteristics of 6005A aluminum alloy flat plates and profiles by laser filler welding method.By adjusting the process parameters,a weld seam with good appearance and stability is obtained under the premise of ensuring penetration.By adjusting the flow of the shielding gas and the magnitude of the heat input,the porosity of the weld is reduced.When the shielding gas flow rate is 15 L/min and the heat input is 165 J/mm,the internal porosity of the weld is the smallest,0.24%.The tensile properties of the welded joints shows that the tensile property is the best when the porosity is the lowest,and the tensile strength is 74.4%of the tensile strength of the base metal.The impact tests shows that the impact toughness of the weld is better than that of the base metal,and the maximum is14.34%higher than that of the base metal,The bending strength of the weld is up to 72.7%of the base metal.The microhardness test analysis shows that there are two softening zones in the welded joint and the overage zone in the heat affected zone.After the welding of the 6005A-T6 aluminum alloy,there is no Mg₂Si phase in the weld,and segregation of Mg,Si and Cu elements exists in the weld.The added ER5356wire can reduce the hot crack sensitivity of the weld by adjusting the content of Mg and Si in the weld to deviate from the high heat crack sensitivity zone.After the post-weld heat treatment of"soild solution+aging",the overall microhardness of the welded joint is greatly improved,the softened area of the joint disappears,and the tensile property is also greatly increased,the tensile strength reaches the strength of the base material,and the elongation is also greatly increased.Under the post-weld heat treatment,theβ"phase（Mg₅Si₆）,β?phase（Mg₉Si₅）and Q?phase(Al_3.8Mg_8.6Si_7.0Cu_1.0)precipitated in the weld.On[001]_Al,there are"flat"and"inserted"forms in the three precipitation strengthening phases.The strengthening effects of the three precipitation to alloy are from large to small:β"phase>Q?phase>β?phase.Post-weld heat treatment makes the number of Al-（Fe,Si,Cr,Mn）impurity phase increasing,from small particle size to large size rectangular plate.The optimized heat treatment specification for laser wire filling welding in this test is:solution temperature 550℃,holding time1.5h,water-cooled;aging temperature 175℃,holding time 8h,air-cooled.Aluminum alloy profiles are welded by Single-time of two-layer laser filler welding.Microhardness test shows that there are many softening areas in the welded joints of the profiles,among which the area between the first weld center and the two fusion zones is the softest.When the scanning speed is increasing,the degree of softening will be decrased.The tensile strength of the welded joint of the profile can reach 85.4%of the base metal,and the elongation will increase or even exceed the base metal due to the rib structure of the profile itself.When the ER5356 welding wire is added for welding,the corrosion resistance of the weld area is enhanced.The numerical simulation of the residual stress and deformation of the profile after welding shows that increasing the welding speed will reduce the high residual stress range（≥150 Mpa）and the deformation degree,and can change the welding deformation degree by changing the welding sequence and constraints.