Tensile deformation behavior of triple heterogeneous microstructure comprising fine equiaxed/coarse equiaxed/columnar grains in AlCu/AlMgSc bimetal fabricated via dual-wire arc direct energy deposition

•An AlCu/AlMgSc bimetallic alloy was prepared using dual-wire arc-DED.•The bimetallic alloy has a triple heterogeneous microstructure (fine/coarse /columnar grains).•The plastic deformation mechanism of triple heterogeneous microstructure was revealed.•The triple heterogeneous microstructure is conducive to trapping GNDs dislocations.•The ρGND is highest in fine grains, followed by coarse grains, and lowest in columnar grains.