In　this　paper,　fibre　laser-cold　metal　transfer　arc (CMT)　and　oscillating　fibre　laser-CMT　hybrid　welding　processes　were　adopted　for　A7204P-T4　aluminium　alloy　sheets　with　thickness　of　6　mm.　Furthermore,　the　effect　of　Nb　content　on　microstructure　and　mechanical　properties,　the　metallurgical　behaviour,　and　influence　mechanism　were　investigated.　Oscillating　laser　effectively　reduced　the　weld　porosity　and　increased　the　joint’s　elongation　after　fracture　by　81%.　With　the　addition　of　Nb,　the　heterogeneous　nucleation　significantly　refined　weld　grains　and　removed　columnar　and　dendritic　structures　which　attributed　to　the　solute　segregation　of　Nb　and　primary　phase　NbAl3.　The　average　tensile　strength　of　joints　with　0.43%,　0.74%,　and　0.83%　Nb　mass　fractions　to　336,　334.5,　and　341　MPa,　respectively.　©　2021　Institute　of　Materials,　Minerals　and　Mining.　Published　by　Taylor　&　Francis　on　behalf　of　the　Institute.