The　micro-joining　of　Al　foil　and　Cu　foil　is　crucial　for　various　industrial　applications,　such　as　manufacturing　power　lithium-ion　batteries　packs　for　electric　and　hybrid　vehicles.　An　ongoing　challenge　in　this　process　is　the　unsatisfactory　joint　strength,　attributed　to　crack　susceptibility　and　poor　joint　ductility.　This　issue　is　primarily　caused　by　the　continuous　formation　of　an　intermetallic　compounds　(IMC)　layer　between　Al　foil　and　Cu　foil.　This　study　investigates　the　microstructure　and　mechanical　properties　of　Al/Cu　lapped　joints　using　laser　spiral　spot　welding　technique　with　a　continuous-wave　(CW)　fiber　laser.　The　research　explores　the　effects　of　keyhole　and　molten　pool　flow　on　joint　morphology　and　microstructure　evolution,　linking　these　aspects　to　joint　fracture　behaviors.　The　results　demonstrate　that　CW　laser　spiral　spot　welding　achieves　defect-free　joints　with　excellent　mechanical　properties.　The　controlled　formation　of　IMC,　alternated　with　ductile　phases,　effectively　restricts　crack　propagation,　enhancing　shear　strength　and　ductility.　Optimal　welding　parameters,　such　as　a　laser　power　of　450　W　and　welding　speed　of　350　mm/s,　yield　joints　with　a　maximum　shear　strength　of　138.2　MPa,　which　represents　a　significant　improvement　over　previous　spiral　spot　welded　joints　and　highlights　the　potential　of　CW　laser　welding　for　efficient　and　high-strength　Al/Cu　metal　foil　joints.　©　2024