Changes in surface structure and mechanical characteristics of Al–5 wt%Si alloy after irradiation by electron beam

The modification of Al–5 wt%Si alloy surface by electron beam in the regimes being different in the energy density of electron beam (10, 20, 30, 40 and 50 J/cm2) and the pulse duration (50 and 200 μs) was performed in the research. It was established that the maximum increase in microhardness was observed at electron beam parameters of 30 J/cm2, 200 μs and 50 J/cm2, 50 μs; and microhardness values for each regime amounted to 860 MPa and 950 MPa, respectively. The microhardness value of the cast alloy equals to 520 MPa. The irradiation surface morphology at beam parameters of 30 J/cm2, 200 μs is characterised by numerous micropores and microcracks. The irradiation regime of 50 J/cm2, 50 μs leads to complete dissolution of intermetallide and silicon particles in surface layer; the crack density per unit of sample surface decreases in comparison with the regime of 30 J/cm2, 200 μs. The surface layer is characterised by the high-speed cellular crystallization structure with dimensions from 500 to 800 nm formed in grain volume that may be the reason for the increase in strength properties of the material.