Structure of Eutectic Al-Si Alloy Subjected to Compression Plasma Flow Impact

The structure and phase composition of a eutectic silumin surface layer modified by compression plasma flow impact were investigated in this work. Plasma flows were generated by a magnetoplasma compressor of a compact geometry in a nitrogen atmosphere. The energy density absorbed by the surface layer was varied in the range of 10–35 J/cm2. X-ray diffraction analysis, scanning electron microscopy, transmission electron microscopy and X-ray microanalysis were used as investigation techniques. It was found that the plasma impact led to the formation of a molten layer with a thickness of up to 50 μm. The layer thickness increased with the growth of the absorbed energy density. Dissolution of the intermetallic compounds and primary silicon crystals occurred as a result. The modified surface layer contained grains of a supersaturated solid silicon solution in aluminum. Grains with sizes of 100–500 nm were separated by interlayers of hypereutectic silumin containing nanocrystalline silicon precipitates. The doping elements of the alloy were concentrated mainly in these interlayers. The plasma impact resulted in a 1.5-fold microhardness increase.