| The application of thick aluminum alloy in large-scale structural parts is increasingly widespread,but the welding problems in its actual production are also becoming increasingly serious.Therefore,it is urgent to develop efficient and reliable welding techniques for aluminum alloy large-scale thick-walled components.Narrow-gap laser welding has become a potential welding method to solve the problem of thick plate welding.It can not only improve the welding efficiency of the plate,but also reduce the welding distortion.The problems of high reflection and porosity in the laser welding process of aluminum alloys,and poor fusion between layers and sidewalls in the narrow gap welding of thick-walled components are critical problems that need to be overcome.Aim to solve these problems,the paper raises a narrow gap laser welding method for thick aluminum alloys.Use high-power laser to achieve thick penetration welding of thick plates to improve welding efficiency;double-focus laser is used to complete multi-layer narrow gap multi-layer filler welding;the unique molten pool flow behavior of the bifocal laser welding mode was studied in detail through high-speed video and numerical simulation methods.And analysis of the interaction with the melting transition of the wire,the final realization of the 50 mm thick 5A06 aluminum alloy plate welding.First of all,through the high-speed video shooting on the surface of the molten pool and plasma shooting,the welding process parameters,the weld pool flow and the corresponding relationship between the weld formation were studied.The results show that,compared with the conventional kilowatt laser,in the high-power laser deep penetration welding of 10,000 watts,the laser action width is increased by 21% when the power is 25 k W,but the penetration depth can be increased by 159%,and the aspect ratio of the weld increases by one.times.Both the increase of laser power and the decrease of the welding speed will make the fluctuation of the molten pool more violent and the quality of the post-weld forming will become worse.The effect of defocusing on the flow of the bath is even more pronounced.In this paper,the effects of single and double focus on the surface characteristics of the molten pool and the melting transition behavior of the welding wire are comparatively studied.Based on the systematic analysis of the bifocal energy field,the behavior of the molten pool and the correlation of the weld formation,it is determined that the narrow gap is suitable for multi-layer filling.Wire Welding Optimized Process Window.The experimental results show that when the bi-focus is arranged in parallel,increasing the distance between the two focal points can effectively reduce the fluctuation of the surface of the molten pool,improve the stability of the fuse,and achieve high-quality welding of 50 mm thick 5A06 aluminum alloy.In order to further elucidate the keyhole behavior and the flow behavior inside the molten pool under different energy modes of the bifocal beam,a heat flux coupling model of bifocal laser welding is established in this paper,and the flow behavior of the molten pool is analyzed for weld formation and pore generation.Influence Mechanism;At the same time,a three-dimensional heat flow coupling model was established for the fusion transition process of the wire,and the influence of the melting wire on the keyhole and the dynamic behavior of the melt pool was analyzed.It provides an important theoretical basis for the control of heat and mass transfer behavior and the optimization of process for bifocal laser filler wire welding. |
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