Ultra-fine Al–Si hypereutectic alloy fabricated by direct metal deposition

•Ultra-fine Al-Si hypereutectic alloy with less than 10 μm primary Si phase.•The unique hypoeutectic microstructure around primary Si in hypereutectic alloy.•The minimum size of eutectic Si.•The maximum microhardness of deposition at a certain laser power.•The mircohardness of deposition is approximately 2.5 times of that of raw alloy.

Ultra-fine Al–Si hypereutectic alloy with <10 μm primary Si phase was fabricated by direct metal deposition (DMD). The microstructure and microhardness of the hypereutectic alloys manufactured under different scanning speeds and laser powers during DMD were investigated. Compared with the conventional modified hypereutectic alloy whose primary Si phase is around 40 μm, the primary Si particle obtained by DMD has a much smaller size of about 5–10 μm. With increased scanning speed and laser power, the volume fraction and size of the primary Si increase. The unique hypoeutectic microstructure can be found around the primary Si phase in the hypereutectic alloy. With increased scanning speed, the size of eutectic Si grain decreases and the microhardness of deposition increase. However, the size of eutectic Si reaches the minimum value at a certain power level, and the microhardness of deposition reaches the maximum value at 850 W laser powers. The mircohardness of the deposited hypereutectic alloy is approximately 2.5 times of that of the raw eutectic alloy.