Research On The Procedure And Porosity Prevention Mechanism Of High-speed Laser Lap Welding For 5182 Aluminum Alloy

Laser welding of aluminum alloys is one of the important technical approaches in automotive light-weighting.1 and 2 mm-thick 5182-O aluminum alloy were welded by a fiber laser in the lap configuration.The effect of defocus,laser power and welding speed on the weld appearance quality and porosity rate were investigated.In addition,the microstructure,microhardness and shear resistance of the welded joints were further studied.The porosity elimination mechanism of high-power and high-speed laser welding were ascertained,so as to provide theoretical basis and experimental basis for the application of high-speed laser welding for aluminum alloys in the white bodywork of automotive bodymanufacturing process.The procedure of high-speed laser welding for aluminum alloys demonstrates that the weld quality is bad and the uneven weld generates lots of undercuts and spatters when the defocus amount is +2 mm.However,when the defocus amount is-2 mm,good weld quality is obtained.Ripple feature is observed and weld surface is smooth.Three types of porosity generated during laser lap welding of aluminum alloys namely hydrogen porosity,process porosity and oxide porosity,can be controlled by adopting appropriate welding parameters.When the defocus amount is-2 mm,the porosity rate of the weld is low.However the weld porosity rate is high when the defocus amount is set to +2 mm.Increasing laser power can increase the porosity rate.When welding speed increases,the porosity rate gets higher firstly,then it has a trend of significant decreasing.With the matching of laser power and welding speed,the porosity rate increases by increasing the weld heat input.Reducing the welding heat input reduces the existence time of the molten pool,allows less hydrogen to dissolve into the molten,reduces the flow time of oxide films and improves the stability of the welding keyhole,which all can reduce the probability of bubbles formation.Meanwhile,the depth of molten pool decreases and the fluid flow of weld pool weakens,which are favorable for the bubbles to float.All of this results in a low porosity rate in the weld.Larger penetration depth,higher depth-width ratio and lower weld porosity rate can be got under the matching of high laser power and high welding speed compared the process of low laser power and low welding speed.No distinct heat affected zone is found in the 5182-O aluminum alloy lap joint.The microstructure near the fusion zone shows columnar grains which are perpendicular to the fusion line.Fine columnar grains with different orientations and equiaxed crystals are observed in the center of weld.The grains in the lower weld center are smaller and more uniformly distributed than that of the upper weld center.The hardness value of the weld is higher than that of the base metal,and the hardness value of the lower weld exceed that of the upper weld.No soft area exists in the joint.Weld porosity is the main factor that affects the shear resistance of the lap joints.The welding process under the conditions of negative defocus,high power and high welding speed can reduce porosity effectively and improve the mechanical properties of the lap joints.When there is a little amount of porosities in the weld,the shear strength of the lap joints reaches 198 MPa.