In　this　study,　A7204-T4　aluminum　alloy　sheet　with　a　thickness　of　6　mm　was　welded　using　fiber　laser　variable　polarity　tungsten　inert　gas　(VPTIG)　hybrid　welding　with　ER5356　filler　wire,　during　which　Nb　(niobium)　foils　with　different　thicknesses　(10　mu　m,　25　mu　m,　35　mu　m,　and　50　mu　m)　were　preset　between　the　butt　joint　faces.　The　joint　microstructure　and　properties　with　different　Nb　content　were　investigated　in　detail.　According　to　the　results　of　this　study,　the　welds　after　Nb　micro-alloying　exhibited　significantly　reduced　pores,　while　Nb-concentrating　phases　and　the　NbAl3　precipitated　phase　gradually　appeared　and　acted　as　heterogeneous　nucleation　particles,　which　can　refine　the　grains.　Therefore,　columnar　crystals　and　secondary　dendritic　crystals　at　the　weld　center　disappeared　and　fine　equiaxed　crystals　appeared.　After　the　addition　of　10　mu　m　Nb　foil　in　the　hybrid　welding,　the　micro-hardness　of　weld　metals　was　significantly　enhanced,　heat-affected　zone　in　the　weld　joint　became　narrower,　and　the　softening　phenomenon　reduced　significantly.　However,　as　the　added　Nb　content　increased,　the　micro-hardness　was　enhanced　less　significantly.　After　Nb　micro-alloying,　the　tensile　strength,　yield　strength,　and　elongation　rate　were　enhanced　significantly.　The　mechanical　performance　of　the　weld　joint　reached　the　optimum　after　10　mu　m　Nb　was　added　in　the　welding　process;　specifically,　the　mean　tensile　strength,　mean　yield　strength,　and　mean　elongation　rate　reached　344　MPa,　269　MPa,　and　6.2%,　respectively,　which　were　91.5%,　89.4%,　and　61.4%　of　those　of　base　metal,　respectively.　The　significant　enhancement　of　weld　micro-structure　and　mechanical　properties　can　be　attributed　to　the　formation　of　effective　nucleation　particles　during　the　solid　solution　of　Nb　in　the　Al　matrix,　thereby　leading　to　grain　refinement　and　a　change　in　the　corresponding　precipitated　phase.