| The new generation of high power fiber laser presents high power with lower beam divergence, which benefits for plates welding. Hybrid welding combines the heat sources of both the arc and the laser beam, which holds the advantages of the both sources and overcomes disadvantages. The hybrid welding has become more and more attractive in recent years.6009aluminum alloy is an ideal material for automobile industry because of its light weight, excellent corrosion resistance, good toughness, and superior strength-to-weigth ratio. However, the researchs have been show that bad weld appearance, porosities, cracks, poor joint properties readily occurred during aluminum plates hybrid welding.The microstructure and properties of joints and welding process of6009aluminum alloy by laser-MIG hybrid welding were studied based on conclusions of the current researches in this paper. Particularly meaningful, the welded joint of laser welding and hybrid welding were comparatively researched. Relationship between hybrid welding parameters of6009aluminum alloy and the homogeneity of weld has been studied in the paper. The influences of welding parameters on deformation of back weld, reinforement, weld width, reinforcement-to-width-ratio, weld width ratio, diameter of laser action zone were investigated. Anode film and electrochemical polishing were employed to analyze the size of weld grain, and Keller’s reagent was adopted to study the precipitation of second phase in weld. Morphologies of porosity and tensile fracture, mechanisms of the deformation of porosity and dimples were analyzed by SEM and EDS. Its aims to lay theoretical foundation for hybrid welding6009aluminum alloy plate in the engineer application. The following are the main results.The research results of hybrid welding formability show that the hybrid welding reinforcement-to-width ratio increased and weld width radio decreased with the increase of laser power, the hybrid welding reinforcement-to-width ratio and width radio increased with the increase of welding current and welding speed. The research of laser welding formability shows that width radio decreased with the decrease of laser welding speed.The results of microstructure during hybrid welding show the MIG arc has mechanical stirring effect for the upper part of hybrid welding seam, and make the stress state of upper pool changed, so lead to the upper welding grain size less than the lower part of it. The effect of arc heat source on fusion and heat-affected zone was studied. The upper part of joint was heated by MIG arc and laser beam together, which resulted in higher heat input and greater the zone of fusion and greater the degree of grain growth.The results of formation mechanism research show that porosity of laser weld are devided into technological and metallurgical porosities.Technological porosity is formed by collapse of laser keyhole. Metallurgical porosities is formed by oxidation film into the molten pool. Porosity of hybrid weld are devided into subsurface and hydrogen porosities. Heat source of MIG arc, through increasing laser keyhole radius, strengthening the ability of plasma radiation, diluting of plasma density, transfers the formation mechanism of porosity from technologic porosities to metallurgical porosities.The study results of mechanical properties of the hybrid joint show that. average microhardness of seam is greater than the heat affected zone, but lower than the parent metal. The microhardness of top hybrid seam is greater than that of bottom. The width of softened zone in HAZ is about4to6mm. The fracture position of hybrid joint transfers from seam to heat-affected zone with the increase of welding speed. The tensile strength of the hybrid joint increase with the increase of welding speed. The tensile strength of the hybrid joint decrease with the increase of laser power. The fracture position of hybrid joint transfers from seam to heat-affected zone with the increase of welding current. The tensile strength of the hybrid joint decrease with the increase of welding current. Dimple morphologies appear in the laser joint and fractures of hybrid joint, but laser joint had the obvious brittle fracture zone. Fractures of Hybrid joint found serpentine pattern. Tensile strength of the laser-MIG hybrid joints has reached63%of the tensile strength of base material, while the tensile strength of laser joint is only38%of that of the base material and the fracture position is in weld. The hybrid joint had softening zone, but laser joint almost have no softening zone. |
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