Microstructure And Properties Of 6009 Aluminum Alloy Laser-MIG Hybrid Welding And MIG Welding Head And Numerical Simulation Of Temperature Field

The welding process of aluminum alloy has been the main factor restricting its industrial application.The traditional gas shielded arc welding, welding depth and welding speed are limited, and there are deformation, porosity and other defects. laser welding speed is fast, the welding efficiency is high, however high reflectivity of the laser beam and low energy absorption efficiency resulted to a limited application of laser welding. The laser-MIG hybrid welding overcome the problem of arc welding and laser welding. The advantages of two kinds of heat sources are concentrated in laser-MIG hybrid welding, Aluminum alloy welded by laser-MIG hybrid welding, not only the welding efficiency improved, but also the welding defects decreased, and the microstructure and properties of the joint can be improved.In this paper, the 6mm thick 6009 aluminum alloy plate was welded by laser -MIG hybrid welding and MIG welding respectively. Then joints of hybrid welding and MIG welding were Comparative studied. The effects of two kinds of joint parameters on the formability of the weld were studied. Using anodic film coating and electrolytic polishing method to study the microstructure of the hybrid welding and MIG welding.The second phase composition was analyzed by EDS energy spectrum analysis. Components of hybrid joint were analyzed by XRD.Tensile fracture morphology of hybrid welding and MIG welding by SEM analysis. Composition of the second phase in dimples was investigated by EDS. Using 3D Gauss conical heat source and double ellipsoid heat source model, With the help of finite element SYSWELD, temperature field of 6mm thick 6009 aluminum alloy laser -MIG hybrid welding process was simulated.Research results show that the forambility of joint when the laser heat source is in the front of the arc heat source is more better than that of the joint that the arc heat source is in the front of the laser heat source in hybrid welding process. Increasing distance between heat sources, Coupling effect of laser heat source and arc heat source is decreased, the laser action area becomes more obvious, Welding symmetry becomes better. In MIG welding process, when welding current increases, the formation of the lower surface of the weld is getting better and better, the height, width and the ratio of the weld width of the weld seam are increased.Microstructure analysis results show that:The grain size in the upper part of the weld joint center is less than the lower part of the weld center of the hybrid welding. Mainly because of hybrid welding process, the arc has a stirring effect on the upper part of the weld pool, this makes the upper melt pool more uniform and the grain size is fine. When the welding current is increased, the grain size of MIG weld will also be bigger. The precipitates at the lower part of the multi pass welding seam are smaller and uniform.The study results of mechanical properties of the joint show that there is a softened zone in the hybrid welding and MIG welding joints.the width of the softened zone of the hybrid welding joint is about 4-5mm, the width of the softened zone of the MIG welding joint is about 6-7mm. In hybrid welding process, when the laser heat source in front of the arc heat source,the average hardness of the upper part of the joint is lower than the average hardness of the lower part of the joint, because the weld seam of alloy elements is burning seriously in the welding process.When the arc heat source in front of the laser heat source,the average hardness of the upper part of the joint is higher than the average hardness of the lower part of the joint. Because of when the arc source in front of the laser source,the laser beam remelted liquid metal that on the upper part of the molten pool, the microstructure is refined, and the surface hardness is improved.The tensile fracture fracture of two joint are located in the heat affected zone.Their dimple walls have serpentine pattern,there are second phase particles in the dimple, that means the formation of the dimple is related to the second phase particles.Numerical simulation of temperature field of hybrid welding head show that, the stability of heat source is not good at the beginning of welding,temperature field peak temperature is slightly lower,at 3 seconds.temperature field become steady state.The peak temperature can reach above 1100℃.The node near the center of the weld,its peak temperature,the heating rate and the cooling rate are larger.The node far away from the center of the weld,ts peak temperature,the heating rate and the cooling rate are smaller.The temperature changes of longitudinal weld and transverse weld of hybrid welding confirms the experimental results of the hybrid welding of precipitates in chapter fourth.