Corrosion Behavior And Mechanism Of Laser Beam Welded Joint Of 2198 Aluminium-lithium Alloy

2198 aluminium-lithium alloy is an ideal material applied in aerospace field due to the favorable properties, such as low density, high specific strength, high temperature resistant, and the high plasticity. Laser welding technology is one of the key technologies for alloy joining. The corrosion resistance of welded joints directly influence the safety and application of the material. So the study of corrosion behavior of welded joint has a realistic significance.Filler wire used in laser welding joint changes the crystal morphology and chemical composition, precipitate species distribution, etc. Joints in corrosive environment easily cause pitting, crevice corrosion and intergranular corrosion and spalling corrosion. The corrosion damages of metal structure, will lead to the mechanical performance decreasing and the service life shortening, etc. So far, the plenty of corrosion behavior study is focused in 2090, 8090 and 1420 Al-Li alloy, less literature can be found about the 2198 Al-Li alloy corrosion resistant performance. So this dissertation investigated the corrosion behavior and corrosion mechanism of 2198 Al-Li alloy laser welding joint using different filling wire.Research results show that 2198 Al-Li alloy parent metal subjects to pitting corrosion. Pitting corrosion occurred from the precipitate phase firstly. Copper-rich area(Rich-Cu) is the pitting initiation point. Due to the existence of electrode potential difference ?E between the precipitate phases and the aluminium metal, galvanic corrosion was happening when they are immersed in the electrolyte. When using the 4047Al-Si filler wire, corrosion way of weld presents the uniform corrosion. This is due to that the addition of Si element promotes the molten pool flowing and the uniform composition distribution during laser welding, which resulting in the grain refining. The rapid cooling also promotes the molten pool recrystallization and precipitates Al-Si eutectic compounds. The dissolution of copper-rich phase results in the composition in the weld more homogeneously, which reduces the galvanic corrosion anode area and decreases the local metal damage. Research also found that the pitting corrosion close to the fusion line zone is serious. When laser welding 2198 Al-Li alloy using 2319Al-Cu filler wire, plenty of copper was found along to the grain boundary. During solidification, some tiny precipitations, such as Al Li, Al2 Cu, Al6 Cu Li3, Al7Cu2Fe7 were precipitated. The existence of these precipitated phases promotes galvanic corrosion. When the joint was immersed in the 3.5w% Na Cl solution, the intergranullar corrosion was found due to the accumulation of Cu along to the grain boundary.Electrochemical polarization curve and impedance spectroscopy analysis showed that corrosion potential of Al-Si filler joint is higher that of Al-Cu filler joint. And the corrosion rate of Al-Si filler joint is lower that of Al-Cu filler joint. Therefore, the corrosion resistance of weld using 2319 Al-Cu filler wire is lower than that of weld using 4047 Al-Si filler wire. This is due to that intergranular corrosion in weld using Al-Cu filler wire results in the partial grain boundary dissolution and the joint damage seriously.