Wire　and　Arc　Additive　Manufacturing　(WAAM)　is　a　combination　of　welding　and　AM　technologies　and　uses　an　electric　arc　as　the　heat　source　to　melt　welding　wire.　The　mechanical　properties　of　WAAM　components　are　greatly　dependent　on　the　solidification　behavior　and　microstructure.　In　this　paper,　a　model　composed　of　a　macroscopic　finite　element　(FE)　model　combined　with　a　microscopic　phase　field　(PF)　model　was　constructed　to　investigate　the　Al　alloy　microstructure　evolution　during　WAAM.　First,　the　FE　model　was　implemented　to　calculate　the　temperature　gradient　and　solidification　speed　under　different　processing　parameters.　These　results　were　then　fed　into　the　PF　model　to　simulate　the　microstructure　and　concentration　field　of　chemical　compositions.　The　simulated　results　indicate　that　the　moving　speed　of　the　substrate　has　a　pronounced　impact　on　the　primary　dendrite　arm　spacing　(PDAS),　which　grew　significantly　as　the　moving　speed　increased,　while　the　PDAS　decreased　slightly　upon　increasing　the　electric　current.　Furthermore,　the　solute　distribution　analysis　showed　that　micro-segregation　formed　during　the　solidification　process,　and　that　current　and　substrate　speed　had　evident　impact　on　the　micro-segregation　ratio.　Finally,　metallographic　experiments,　energy-dispersive　spectrometer　analysis　for　element　distribution,　and　miniature　tensile　tests　were　conducted　on　the　specimens　to　validate　the　PF　simulated　results　and　obtain　the　relationship　between　process　parameters　and　mechanical　properties.　©　2020