The technology of laser fusion on a powder bed is modified for the manufacture in air, of multi-material parts formed in the three dimensions of space, with zones which can be either a dielectric ceramic, based on alumina, or an aluminum-silicon metallic conductor. This additive manufacturing method uses only one powder. This powder is an AlSi12 alloy previously activated by a chemical treatment, which gives it, increased reactivity to oxygen. Therefore, the only adjustment of the manufacturing conditions, through the power and the scanning speed of the laser, as well as the hatch spacing, makes it possible to choose the construction of ceramic or metallic type zones. The modification of AlSi12 powders by chemical activation is the subject of a detailed characterization, allowing the selection of treatment conditions adapted to the multi-material manufacturing process. The ceramic or metallic areas that are produced, are also characterized for subsequent use of this process, for the manufacturing of microwave devices dedicated to the space industry.