Butt　joints　of　3.0　mm　thick　sheets　of　an　Al-Li　based　alloy　have　been　produced　using　Nd:YAG　laser　welding　without　filler　metals.　The　hardness　distribution　and　microstructure　of　the　alloy　and　welded　joints　were　investigated.　The　changes　in　the　grain　shapes,　grain　orientations,　microtexture,　and　precipitates　of　the　fusion　zone　were　analyzed　using　optical　microscope,　electron　back　scattered　diffraction　(EBSD)　and　transmission　electron　microscopy　(TEM).　The　results　show　that　Nd:YAG　laser　welding　leads　to　a　change　of　the　microhardness,　grain　shape,　grain　orientations,　and　a　disappearance　of　the　microtexture　and　precipitates.　A　narrow　band　of　EQZ　along　the　fusion　boundary　and　a　predominantly　equiaxed　dendritic　structure　are　developed　in　the　fusion　zone.　The　formation　of　the　predominately　equiaxed　dendritic　grains　is　due　to　a　heterogeneous　nucleation　mechanism　aided　by　equilibrium　A1(3)Zr　phases　as　well　as　the　growth　of　pre-existing　nuclei　created　by　dendrite　fragmentation,　or　by　grain　detachment　resulted　from　Nd:YAG　laser　welding　processes.　In　addition,　Nd:YAG　laser　welding　produces　lower　Vickers　hardness　than　that　of　the　base　metal　due　to　the　decrease　in　the　in　quantity　of　delta＇　precipitates　in　the　fusion　zone.　(C)　2012　Elsevier　Inc.　All　rights　reserved.