| Stainless steel and copper have been widely used in many consumer electronic products.the research on the parameters and reasons that affect the strength of laser welding of stainless steel and copper dissimilar metals has important theoretical significance and practical application value for laser welding of steel-copper dissimilar metals.This article mainly conducts research on laser lap welding of dissimilar metals of stainless steel SUS303 and C19120 copper plates with thicknesses of 0.2 mm.Two different welding equipment(Millisecond fiber laser and nanosecond pulsed infrared fiber laser),using the lap welding method of stainless steel on top and copper on the bottom.Aiming at the characteristics of different lasers,experiments were designed based on the controlled variable method,and the influence of the welding parameters of the two lasers on the appearance and mechanical properties of the welding under the interaction of a single variable and multiple factors was studied.The peak power,pulse width and energy of millisecond fiber lasers that have the greatest impact on the appearance and mechanical properties of welding were found,but the adjustment of the parameters required for welding appearance and welding strength could not meet the specifications.When the nanosecond laser selects the appropriate welding speed,power,waveform and swing frequency,it is possible to obtain a lap joint with appearance and welding strength that meets the requirements of use.Then,through methods such as metallographic analysis,SEM,EDS,and microhardness analysis,the surface morphology,cross-section surface morphology,molten pool composition and molten pool slices of different equipment under the optimal welding parameters were systematically compared and analyzed.Find out how different equipment affects welding strength.The study found that the millisecondlevel laser welding pool is bowl-shaped.During the welding process,the two metal liquids will produce convection,and because the welding time is millisecond-level,a large number of cellular dendrites and grains are found on the side of the weld on the steel side.Growing perpendicular to the rigid surface and the boundary of the molten pool,α-Fe is dispersed in the weld zone of the steel melting joint,showing small equiaxial crystals,and the interface layer is a solid solution composed of a small amount of ε-Cu and a large amount of α-Fe.And the transition zone with a large number of granular phase regions appears near the weld joint on the copper side.The second type of nanosecond laser welding molten pool is nail-shaped,and the area of the molten pool at the lower part is very narrow,so it is difficult for copper to reach the upper part of the molten pool,and because the time of a single welding spot is nanosecond,the welding has been completed before copper and stainless steel reacted to each other.Although dendrites are also found in the weld on the steel side,the size is smaller than the first welding method and the crystal grains at the junction of the copper side weld are not significantly become larger.During the welding spot strength test,the joint sample of the first welding method was fractured on the copper side,with dimple morphology.It was ductile fracture caused by insufficient strength of the copper layer at the bottom,while the second joint sample was fractured on the steel side.The columnar crystal structure at the edge of the weld pool could be observed at the fracture surface,which was brittle fracture along the crystal.In summary,Nanosecond lasers have great advantages in welding appearance and strength when performing lap welding of thin steel-copper dissimilar metals. |
