THE MORPHOLOGY AND MICROHARDNESS OF THE SURFACE OF AK5M2 ALLOY IRRADIATED BY AN ELECTRON BEAM

The study objective was to analyze the change in the morphology and microhardness of the AK5M2 alloy irradiated by an electron beam in various regimes. The authors modified the Al-5wt%Si alloy surface by an electron beam in the modes differed in the electron beam energy density (10, 20, 30, 40, and 50 J/cm²) and pulse durations (50 and 200 μs). The study identified that at electron beam parameters of 30 J/cm², 200 μs, and 50 J/cm², 50 μs, the maximum increase in microhardness to 860 MPa and 950 MPa was observed for each of the regimes, respectively. The microhardness value of the cast alloy was 520 MPa. Numerous micropores and microcracks characterize the irradiation surface morphology at beam parameters of 30 J/cm², 200 μs. The material shrinkage during its high-speed crystallization can cause the formation of micropores. It is possible to assume that the generation of tensile stresses in a surface layer resulted from high cooling rates of a surface layer of the material from the molten state causes the formation of microcracks. The irradiation mode of 50 J/cm², 50 μs leads to the complete dissolution of intermetallic and silicon particles in a surface layer; the crack density per surface area unit of the sample decreases against the regime of 30 J/cm², 200 μs. The surface layer is characterized by the structure of high-speed cellular crystallization with the sizes of 500 to 800 nm formed in the volume of the grains that may cause an increase in the strength properties of the material.

Al-5wt%Si alloy, electron beam, microhardness, cellular crystallization