Modification of microstructure and mechanical property of hypereutectic Al–Si alloy by laser surface remelting

CO2 laser irradiation has been applied to modify the surface of hypereutectic aluminum (Al–23 mass%Si, Al–30 mass%Si) cast alloys. Laser beam, 3 mm in diameter, was irradiated on the alloy surface by moving them with constant velocity (5 mm/s) with beam oscillation of 5 mm in width and 100 Hz in frequency perpendicular to travel direction at 2.3 kW laser power. A part of alloy surface was partially remelted by laser irradiation. After laser beam passed, it was naturally quenched because stored heat was absorbed in specimen. The microstructure of the surface remelted layer consists of primary Si particle, primary α phase and α–Si eutectic phase. These all were very fine. The mean diameter of primary Si was about 12 μm at Al–30 mass%Si. The tensile strength of the surface remelted layer was 254–264 MPa, which was improved to about 1.8 times as that of as-cast material. In dry sliding wear against a steel counter surface, the wear resistance of the surface remelted layer was improved to 1.5–3.0 times as that of as-cast material.