Metal additive manufacturing is leading a paradigmatic shift in multiple industries such as aerospace and biomedical. In particular, laser powder bed fusion (LPBF) is a state-of-the-art additive manufacturing technique for the layer-by-layer production of metallic components using a laser beam to locally melt a metal powder bed. A new Al alloy - Aheadd® CP1, has been developed that is specifically tailored to exploit the rapid solidification nature of LPBF, resulting in stable microstructures that do not require extensive post-processing. High-resolution synchrotron Nano-Tomographic characterizations were performed to reveal for the first time in 3D the internal structure of the microstructural constituents within the prior melt pools. The results elucidate the intra- and intergranular structures that are specific to this LPBF alloy and that determine its performance.