Aluminum-based alloys alloyed with transition metals (Fe, Mn, Ni, Cr) were studied in this work. The structure and hardness in as-cast state and after laser melting within the range of conditions identical to those of the selective laser malting and after laser melting and heat treatment were studied. It was established that, the microstructure of Al-2FeMn and Al-2.5FeCr alloys in the as-cast state was characterized by the presence of dendrites of the aluminum solid solution surrounded by Al3(Fe, Mn) and Al6Mn phases in the alloy with Fe, Mn, and Al3(Fe, Cr) and Al7Cr phases in the alloy with Fe, Cr. Al-4.5FeMn, Al-6FeMn, Al-4.5FeNi, and Al-3FeCr alloys were distinguished by the presence of Al6Mn, Al3Fe and Al7Cr angular-shaped primary crystals, respectively. The microstructure of alloys after laser melting (36.7 W) was characterized by a much dispersed structure of dendrites and eutectics. It was established that the average dendritic cell size decreases from 0.45 to 0.2 microns with an increase in the concentration of alloying elements from 2 to 6 % mass. It was established that during laser melting by several sequential pulses, a transition zone is formed at the boundary with the previous pulses. Microstructure of this zone differs from that of the center. It was shown that the microstructure of Al-2FeMn, Al-4.5FeNi, and Al-2.5FeCr alloys is characterized by a large dendritic cell size of 1.7-2.2 μm. The microstructure of Al-4.5FeMn, Al-6FeMn and Al-3FeCr alloys in the transition zone is characterized by the presence of primary crystals of Al6Mn and Al7Cr phases, respectively. Their formation is associated both with a decrease in the cooling rate at the first moment of crystallization of the melt pool, and with a high content of alloying elements. It was shown that primary crystals were not found in alloys where the content of transition metals was less than 3-4 %. It was also shown that Al-4.5FeMn, Al-6FeMn, and Al-4.5FeNi alloys are characterized by high hardness, which is within 89-93 HV. The hardness of Al-2FeMn, Al-2.5FeCr, and Al-3FeCr alloys alloyed with transition metals in the content of less than 3 % is lower and amounts to 56-60 HV. Al-4.5FeMn, Al-6FeMn, and Al-4.5FeNi alloys are characterized by high thermal stability of the intermetallic phases when heated to 300 °C, as evidenced via a decrease in hardness by 7-10 HV only. The lowest thermal stability had the alloys alloyed with iron and chromium. When heated to 300 °C, hardness of these alloys decreases by 10-18 HV. An effect of the laser radiation power on the grain structure of the alloys is established. It is shown that the large grains with a crystallographic orientation similar to that of an epitaxial layer are formed in the alloys at a low melting power of 26.3-36.7 W. In case of an increase in power up to more than 42.7 W, a central zone consisting of smaller crystals with 58 μm in average size appears in the structure of the treated region. Their formation is associated with a significant increase in the melt volume and an independent nucleation of solid phases.
