Research On Effect Of Niobium Powder On Weld Quality Of Aluminum Alloy In Laser-Arc Hybrid Welding

Due to their excellent physical and mechanical properties, aluminum alloys have been extensively applied in machinery, electric power, aerospace, ships and vehicles industry, becoming one of the most widely used light metals. Because of the suddenly decreased hydrogen solubility, pores are easily created during the welding procedure. And the service life of the aluminum alloys parts is directly affected by corrosion properties of weld. It's of great significance that taking researches on weld pores and corrosion properties in aluminum laser-arc hybrid welding. The low power YAG laser and TIG hybrid welding experiment of 6061 aluminum alloy plates was conducted, the effect of niobium powder on weld formation, pores distribution and porosity were researched by niobium addition slotted on aluminum plate, the influence of niobium powder on weld microstructure and electrochemical corrosion properties was analyzed by EPMA and SEM. The corrosion morphology was also discussed at last.(1) Process experiments. Appropriate niobium powder linear addition was selected according to the weld formation by slotted on aluminum plate. The density of niobium powder was reexamined and the method of how to calculate niobium powder addition was proposed. The welds with good surface quality formed under these conditions, niobium powder addition 0-13.6 mg/cm, laser power 400 W, arc current 400 A, flow of shielding gas 9 L/min, welding speed 300 mm/min. The weld penetration and width increase. The niobium powder affects weld penetration more than width.(2) The effect of niobium powder on pores. A appropriate addition of Nb powder can well depress the formation of pores in aluminum alloys laser-arc hybrid welding. The pores number and porosity were both significantly decreased, compared with normal weld. Nb powder can reduce the number and max diameter of pores in each area at penetration direction. The number of pores gradually decreases from top to bottom of weld no matter with Nb or not. The pores number in left area was equal to the right, which shows symmetrical and random characteristics.(3) The Nb powder refined grain of weld, made columnar crystal transform to isometric crystal; promoted bubbles nucleation and the fusion, increased the pores diameter, reduced the viscosity of molten metal, which resulted in the bubbles escape velocity increased; reduced severe convection of molten metal, conducing to the stability of keyhole; using hydrogen absorption properties reacted with hydrogen during the molten time, reduced the number of free hydrogen; which depressed pores formation.(4) The effect of niobium powder on corrosion property. Transition passivation didn't appear for base metal and weld with no Nb. All welds didn't passivate obviously. Pitting potentials of all samples were close. Corrosion rate of welds with Nb were decreased to a large extent, but corrosion tendency had no great influence. The SEM observation of surface after corrosion shows that the welds with Nb had smooth flat surfaces and less corrosion pits compared to the base metal and weld with no Nb. Nb powder increased the corrosion property of aluminum alloy weld in laser-arc hybrid welding to some extent, made the corrosion morphology more compact. The nonuniform corrosion happened when the Nb powder addition was too high.