Wire arc additive manufacturing of the Al-5.55Cu alloy: Insight the effect of intrinsic heat treatment on microstructure and mechanical properties

Al-5.55Cu alloy single wall sample were fabricated by cold metal transfer wire arc additive manufacturing (CMT-WAAM) technique, and the microstructure characteristics and evolution mechanism of the different deposition regions were analyzed. Under the influence of intrinsic heat treatment and remelting process caused by layer-by-layer deposition, the top region exhibits dendritic characteristics, while the middle and bottom are characterized by a non-uniform banding distribution of fine equiaxial grains alternating with columnar grains. According to the non-equilibrium solidification theory and the related nucleation mechanism, the formation of equiaxed grains in the inter-layer region is related to the elements such as Ti and Zr contained in Al-5.55Cu alloy, which can be used as nucleation particles. In addition, the morphology and quantity of the θ'-Al2Cu phase inside the grain change with the increase of deposition height due to the thermal cycling effect. After heat treatment, the tensile strength of the deposited sample is greatly improved and remains isotropic. The ultimate tensile strength of the heat-treated sample is 508.0 ± 18.9 MPa in the horizontal direction and 503.8 ± 6.2 MPa in the vertical direction.