Special Features of Structure and Phase Transitions of Al – Fe – Cr Alloy under Different Crystallization Conditions in Additive Technologies

The microstructure of alloy Al – 2.5% Fe – 1.5% Cr obtained by crystallization from melt at cooling rates of 0.5 – 940 K/sec and the effect of the type of the initial microstructure on the behavior of the alloy under laser treatment are studied. An x-ray phase analysis of cast alloys is conducted, the solidus temperature and the microstructure are determined. The Thermo-Calc software is used to plot polythermal sections of the Al – Fe – Cr system, and the changes in the mass fraction of the hard phases in the structure are computed. It is shown that elevation of the cooling rate in crystallization of the alloy causes decrease in the concentration of the primary crystals of the Al45Cr7 phase until their total disappearance and formation of a homogeneous microstructure. The surface of the specimens is treated with a laser beam, and then the microstructure of cross sections of the tracks obtained is investigated. This type of surface treatment imitates the impact on the material in additive technologies. Laser treatment of the surface of the alloy raises the hardness substantially (from 43 to 77 HV), which is explainable by formation of a supersaturated aluminum solid solution and a small size of the dendrite cells.