Laser Welding Of Aluminum Alloy With Different Thickness And Numerical Simulation

Tailor-welded Blank (TWB) is one of the most important technologies in automobile body manufacture in recent years, whose welding quality and residual stresses and deformation have great effects on the following stamping process and its performance properties. In this paper, CO₂ laser welding of aluminum alloys sheet with different thickness with the addition of filler metal powder was studied. The main factors affecting welding process stability and formability of weld were investigated. And the mechanism of improving the process stability with the addition of filler mental powder was indicated further. TWBs with well quality of weld joint and formability of weld were obtained. Moreover, temperature field and the stress-strain field of aluminum alloy with different thickness on laser welding were simulated based on the finite element analyses (FEA), a new heat source model in laser full fusion welding was proposed, and the residual stresses distribution and deformation features of TWB were analyzed. All these results provide experimental and theoretical foundations for predicting and controlling the residual stresses and deformation and optimizing the process of laser welding and stamping.CO₂ Laser welding of 5052 and 5056 aluminum alloys sheet with different thickness was performed with or without the addition of filler metal powder and powder The main factors affecting welding process stability and the every welding parameter affecting formability of weld were investigated. The results indicate that with the increasing of magnesium in aluminum alloys, the absorptivity is also improved and the critical power density can be reduced, so a stable welding process can be obtained for a higher content of magnesium in aluminum alloys. The stability of plasma is improved for laser fusion welding, so the process stability and formability of weld can be improved greatly.Furthermore, using scanning electron microscopy(SEM), Electron probe (EPMA) atomic absorption spectrometry(AAS), micro-hardness tests and tensile tests, the microstructure and mechanical characteristics of the welded joints were evaluated, loss of magnesium through vaporization from the fusion zone and fracture surface were analyzed. The microstructure of the welds center is cellular dendrite structure, the loss of magnesium increase with increasing magnesium content for aluminum alloys. The hardness of 5052 aluminum alloys welds with the addition of filler metal powder is harder than that without the addition of filler metal powder, the main reason is the magnesium of metal powder can compensate the loss of magnesium. At the HAZ of thinner sheet, hardness is lower than the base metal. But for 5056, hardness of welds of TWB is about equal to base metal for two welding process with or without the addition of filler metal powder. The total elongation in the longitudinal direction for the laser welds decreased greatly. The specimens of the TWB of 5052 aluminum in the transverse tensile all are fractured on the HAZ of the thinner base metal, the main reason is the thinner base metal of half-harded state was annealed during welding course, But ones of 5056 aluminum are all fractured on the thinner base metal away from weld. The ductibility of the TWB is affected by percent of the sheet with better ductibility in a TWB. The total elongation increases with the percent of the sheet with better ductibility increasing. The ductile fracture is dominated for the transverse tension specimen.Finally, based on the FEA, temperature field and the stress-strain field of aluminum alloy with different thickness on laser welding were simulated. By investigating thermal effect of heat source and weld shape for laser full fusion welding of aluminum alloy with different thickness, a new heat source model named plane-stereo-plane combined heat source model in laser full fusion welding was proposed. The programs are compiled to apply load of moving heat source by ANSYS' APDL program. The effects of temperature-dependence material parameters and fusion enthalpy, boundary conditions, plasma, shielding gas and characteristics of different thickness were considered. The simulated results indicate that temperature field distribution is unsymmetrical, the temperature field distribution was measured by high-temperature thermocouple. It is shown that the simulated results are in accordance with the experimental results.The two different heat source models are used, they are plane-stereo combined heat source model and plane-stereo-plane combination heat source model. Based on the two heat source models, the two different weld pool shapes and temperature field are simulated and analyzed by 3D transient thermal FEM analysis for aluminum alloy with different thickness on laser welding. It is shown that the shape of weld is in more accordance with actual back bead forming by the new combination heat source model.Based on simulated results of temperature fields, stress-strain field was simulated. Effects of temperature-dependence material parameters were considered in the model. The BKIN was established for plastic analysis. The simulated result indicates that, the distributions of the stress-strain are asymmetric, the distributions of stress-strain field in the thinner plate are larger than the thicker one. The residual-stress was measured by hole-drilling method. At the same time, the angular deformations of TWB were measured. It is shown that the simulation results are in accordance with the experimental results.