2198　aluminium-lithium　alloy　is　extensively　used　in　the　field　of　aerospace　due　to　the　favorable　properties,　such　as　low　density,　good　mechanical　property,　high　specific　strength,　good　thermostability　and　plasticity.　2198　aluminium-lithium　alloy　is　welded　by　fiber　laser　using　the　filler　of　ER4047　Al-Si.　The　microstructure　and　corrosion　behavior　of　joint　in　NaCl　solution　with　3.5%　mass　fraction　is　studied.　The　micromorphologies,　precipitate　species　and　their　distribution　have　been　examined　using　the　optical　micrograph,　scanning　electron　microscope　and　transmission　electron　microscope.　The　corrosion　behavior　of　weld　and　base　metal　has　been　compared　by　the　methods　of　immersion　test　and　electrochemical　corrosion　test　at　room　temperature.　The　results　indicate　that　the　microstructure　of　2198　aluminium-lithium　alloy　base　metal,　compared　to　the　weld,　is　coarser　and　grows　along　to　the　rolling　direction.　Plenty　of　T1　precipitates　with　the　diameter　of　hundreds　of　nanometers　distributed　randomly　in　the　base　metal.　After　laser　welded　with　the　filler　ER4047　Al-Si,　the　heat　affected　zone　is　narrow,　the　microstructure　is　tiny,　the　component　is　uniform,　the　kind　of　precipitate　is　various,　and　the　fine　grain　is　equiaxed,　the　columnar　crystal　is　vertical　growth　close　to　fusion　line.　At　room　temperature　in　NaCl　solution　with　3.5%　mass　fraction,　the　weld　and　heat　affected　zone　show　the　uniform　corrosion　behavior,　the　small　corrosion　spot　area,　the　shallow　corrosion　spot.　By　comparison,　the　parent　metal　shows　the　pitting　corrosion.　With　the　immersion　time　increasing,　the　pitting　area　is　enlarged　and　the　depth　is　deeper.　The　open　circuit　potential,　self-corrosion　potential　and　polarization　resistance　of　weld　are　all　higher　than　those　of　the　parent　metal,　but　the　corrosion　current　density　is　less　than　that　of　the　parent　metal.　©　2016,　Chinese　Lasers　Press.　All　right　reserved.