This study investigates the in-situ precipitation of Mn and Cr-rich precipitates during the annealing of a novel Al-Mn-Cr-Zr alloy using in-situ synchrotron scanning X-ray fluorescence measurements. Al alloys have been specifically designed for powder bed fusion-laser beam (PBF-LB) additive manufacturing, by considering the extended non-equilibrium solid solubility of Mn and Cr in Al achieved by the extremely high cooling rates present in the PBF-LB process. During post-printing annealing, controlled precipitation of these solutes increases the material hardness substantially. During an annealing time of 24 hours, we observe in situ the nucleation and growth of two different types of Mn and Cr-based precipitates. The nano focussed X-ray probe at the P06 beamline at DESY, Germany, coupled with a new annular XRF detector enabled us to study this process both with a sufficient temporal and spatial resolution to observe the diffusion of elements in the Al matrix, and their subsequent agglomeration into precipitates. By understanding and quantifying the kinetics of this process, new material compositions and heat treatments can be designed for optimal mechanical properties.