Feasibility study of laser surface remelting on Al-Ni casting alloy

Al-Ni alloy is an alternative alloy for high-temperature applications because of their high stability of Al3Ni eutectic fibers. However, the matrix of eutectic Al-Ni is weak, so that there are many studies attempting to overcome this weakness. A famous method is to use laser for remelting the alloy surface. The objective of this study is to reveal the feasibility of laser surface remelting on Al-Ni casting alloy. Laser spot diameter, scan speed, and laser power were set at 100 μm, 200 mm/s and 80 W, respectively. Three levels of laser pulse frequency, i.e., 100, 300 and 500 kHz, were applied in the single-line melting and areal melting processes. The results revealed that the use of different laser frequencies caused the different microstructures and microhardness of the laser-molten region. The laser frequency of 500 kHz provided a good result for the microhardness and microstructural aspects. The hardness of laser-molten zone for the single-line and areal melted samples was 63.02 and 78.61 HV, respectively, which were 1.3 and 1.7 times the hardness of untreated Al-Ni casting alloy. Although the surface hardness caused by the 500-kHz laser frequency was less than 100 kHz, the microstructure of the laser-molten zone was of more complete uniformity and less defects.